彻底明白Activity启动模式-SingleTop、SingleTask、SingleInstance具体使用场景

启动模式

启动模式是什么

有这样的场景：

• 当我们使用App的时候，呈现出一个Activity，按下返回键（不考虑重写返回键事件），常常就回退到上一个打开的Activity或者退出App。

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//重写返回按键事件</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> boolean <span class="hljs-title" style="box-sizing: border-box;">onKeyDown</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> keyCode, KeyEvent <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">event</span>) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (keyCode == KeyEvent.KEYCODE_BACK && <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">event</span>.getRepeatCount() == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 这里重写返回键</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>; }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

• 几个应用之间，例如我的App要使用拍照功能，我需要调用系统的相机App，这分明就是两个不同的应用程序，分别运行在不同的进程，但是当我调用完成相机后，按下返回键可以返回我的App

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调用相机</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">openCamera</span>() { Intent takePictureIntent = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Intent(MediaStore.ACTION_IMAGE_CAPTURE); uri = PhotoUtil.createImageFile(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (takePictureIntent.resolveActivity(mContext.getPackageManager()) != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 相机被卸载时不会崩溃</span> takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, uri); startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAMERA); } }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

• 还有例如在我们的App打开浏览器、微博之类的应用，然后跳转到浏览器，使用完成浏览器的功能，不断按下返回键，可以回到我们的应用。而不是像点击桌面上浏览器图标启动浏览器那样，不断返回键，最后回到的是桌面。
• 生成重复页面。 
  以前遇到过这样的Bug： 
  
  1. 消息推送，通知栏弹出Notification，点击Notification跳转到指定Activity，但是如果我现在页面就停留在那个指定的Activity，会再次打开我当前的Activity，这样返回的时候回退的页面和当前页面一样，感官上就会很奇怪。
  2. 登录的时候，登录成功跳转到主页，按下两次登录按钮，生成了两个主页。一些有启动延迟的页面（往往是动画，网络造成）也会有这样的情况。

为什么要研究启动模式

1. 有时候我们的App需要生成给其他App调用的Activity，例如浏览器应用，照相机应用
2. 解决生成重复页面等等Bug
3. 任务栈过深的时候，避免一直按返回键也退不回想要的页面

任务栈

任务栈Task，是一种用来放置Activity实例的容器，他是以栈的形式进行盛放，也就是所谓的先进后出，主要有2个基本操作：压栈和出栈，其所存放的Activity是不支持重新排序的，只能根据压栈和出栈操作更改Activity的顺序。

启动一个Application的时候，系统会为它默认创建一个对应的Task，用来放置根Activity。默认启动Activity会放在同一个Task中，新启动的Activity会被压入启动它的那个Activity的栈中，并且显示它。当用户按下回退键时，这个Activity就会被弹出栈，按下Home键回到桌面，再启动另一个应用，这时候之前那个Task就被移到后台，成为后台任务栈，而刚启动的那个Task就被调到前台，成为前台任务栈，手机页面显示的就是前台任务栈中的栈顶元素。

standard

Activity默认模式，所有的Activity遵循元素进栈出栈的特性，例如进栈序列为A->B->C->D,D呈现在页面上，按返回键出栈顺序久违D->C->B->A. 
在

singleTop

栈顶复用模式，如果要开启的activity在任务栈的顶部已经存在，就不会创建新的实例，而是调用 onNewIntent() 方法。避免栈顶的activity被重复的创建。 
在开始处，我们提到的2个Bug,可以用这种模式解决

消息推送

通知栏弹出Notification，点击Notification跳转到指定Activity，但是如果我现在页面就停留在那个指定的Activity，会再次打开我当前的Activity，这样返回的时候回退的页面和当前页面一样，感官上就会很奇怪。

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> btnNotification.setOnClickListener(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OnClickListener() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onClick</span>(View v) { NoticationUtil.sendNotication(mContext); } });</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">public class NoticationUtil { @SuppressLint(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"NewApi"</span>) public static void sendNotication(Context context) { // 在Android进行通知处理，首先需要重系统哪里获得通知管理器NotificationManager，它是一个系统Service。 NotificationManager manager = (NotificationManager) context <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getSystemService</span>(Context<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.NOTIFICATION</span>_SERVICE)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> PendingIntent pendingIntent = PendingIntent<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getActivity</span>(context, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, new Intent(context, MainActivity<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>), <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> // 通过Notification<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>来创建通知，注意API Level // API16之后才支持 Notification notify = new Notification<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>(context) <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setSmallIcon</span>(R<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.drawable</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ic</span>_launcher) <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setTicker</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"您有新短消息，请注意查收！"</span>)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setContentTitle</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"我是标题"</span>) <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setContentText</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"点我打开主页"</span>)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setContentIntent</span>(pendingIntent) <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setNumber</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> notify<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.flags</span> |= Notification<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.FLAG</span>_AUTO_CANCEL<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">; // FLAG_AUTO_CANCEL表明当通知被用户点击时，通知将被清除。</span> manager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.notify</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, notify)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> } }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul>

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity </span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.MainActivity"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:launchMode</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"standard"</span> ></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">action</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.action.MAIN"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">category</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.category.LAUNCHER"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

修改为：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity </span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.MainActivity"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:launchMode</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"singleTop"</span> ></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">action</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.action.MAIN"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">category</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.category.LAUNCHER"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

登录的时候

登录成功跳转到主页，按下两次登录按钮，生成了两个主页。一些有启动延迟的页面（往往是动画，网络造成）也会有这样的情况。

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> btnLogin.setOnClickListener(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OnClickListener() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onClick</span>(View v) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 延迟1000秒，模拟网络超时</span> v.getHandler().postDelayed(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 登录成功,跳转到主页</span> LoginSuccessActivity.actionStart(mContext); } }, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3000</span>); } });</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

XML清单配置

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.LoginSuccessActivity"</span> /></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

 
把他修改为singleTop

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity </span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.LoginSuccessActivity"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:launchMode</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"singleTop"</span> /></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

耗时操作返回页面

还有一种场景 从activity A启动了个service进行耗时操作，或者某种监听，这个时候你home键了，service收集到信息，要返回activityA了，就用singleTop启动，实际不会创建新的activityA，只是resume了。不过使用standard又会创造2个A的实例。

singleTask

栈内复用模式

1. 如果要启动的Activity在当前栈内启动，activity只会在任务栈里面存在一个实例。如果要激活的activity，在任务栈里面已经存在，就不会创建新的activity，而是复用这个已经存在的activity，调用 onNewIntent() 方法，并且清空这个activity任务栈上面所有的activity。

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.MainActivity"</span> ></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">action</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.action.MAIN"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">category</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.category.LAUNCHER"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity </span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.Test1Activity"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:launchMode</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"singleTask"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.Test2Activity"</span> /></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

XML配置 MainActivitiy，Test2Activity为standard模式，Test1Activity为singleTask模式。 
入栈情况： 
MainActivity—>Test1Activity—>Test2Activity—>MainActivity,如果此时启动Test1Activity，会清空Test1顶部元素 栈内情况变为MainActivity—>Test1Activity； 
 
2. 主要就是在清单文件中配置Android:taskAffinity="新的包名"，因为android:taskAffinity这个字段默认指定的包名为本应用的包名，表示在本应用包名的任务栈内创建应用。如果设置了这个字段，而且还和本应用包名不同，就会在新的任务栈创建任务。例如，修改刚才的代码Test1Activity的配置清单：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity </span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.Test1Activity"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:launchMode</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"singleTask"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:taskAffinity</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"com.test.newlaunch"</span> /></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

指定android:taskAffinity包名为com.test.newlaunch 

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">46.556</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): id:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">69</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">46.556</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): numActivities:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">46.556</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): topActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MainActivity</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">46.556</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): baseActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MainActivity</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">48.428</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): id:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">69</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">48.428</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): numActivities:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">48.428</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): topActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Test</span>2Activity <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">48.428</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): baseActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MainActivity</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50.080</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): id:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">69</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50.080</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): numActivities:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50.080</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): topActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MainActivity</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50.080</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): baseActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MainActivity</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">55.164</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): id:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">71</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">55.164</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): numActivities:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">55.164</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): topActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Test</span>1Activity <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">55.164</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): baseActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Test</span>1Activity <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">56.688</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): id:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">71</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">56.688</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): numActivities:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">56.688</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): topActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Test</span>2Activity <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">56.688</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): baseActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Test</span>1Activity <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58.140</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): id:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">71</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58.140</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): numActivities:--<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58.140</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): topActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MainActivity</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">47</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58.140</span>: D/displayTask(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22127</span>): baseActivity:--<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.example</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.testlaunch</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.aty</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Test</span>1Activity</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul>

最开始的栈id为69，然后在06-03 14:47:55.164: D/displayTask(22127): topActivity:--com.example.testlaunch.aty.Test1ActivityTest1Activity启动的时候又新建了一个栈id为71.同时在查看后台程序，看到出现了2个后台任务都是我们的应用—TestLanuch。

作用

1. 做浏览器、微博之类的应用，比如其他App需要打开我们的浏览器页面，就可以配置他为singleTask模式，保证他只有一个唯一实例，节约内存同时按下返回键后的感官也更顺畅。但是需要注意，提供给人调用的页面最好是栈底元素。因为，如果自己的客户端处于运行状态，按下Home键后台挂起。此时如果使用如果其他应用（比如说QQ）调起自己的客户端某个页面，不做任何处理的情况下，按下回退或者当前 Activity.finish()，页面都会停留在自己的客户端（因为自己的Application回 退栈不为空），这明显不符合逻辑的。 
   对于我的应用TestLaunch XML清单配置

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.MainActivity"</span> ></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">action</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.action.MAIN"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">category</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.category.LAUNCHER"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity </span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.Test1Activity"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:launchMode</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"singleTask"</span> ></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">action</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.Test1Activity"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">category</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.category.DEFAULT"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".aty.Test2Activity"</span> /></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>

在其他应用 “我是QQ”中打开指定页面Test1Activity

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> btnSkip.setOnClickListener(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OnClickListener() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onClick</span>(View v) { Intent intent = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Intent(); intent.setAction(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">".aty.Test1Activity"</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { startActivity(intent); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (Exception e) { e.printStackTrace(); } } });</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>

错误重现

a. 模拟操作TestLanuch 
 
b. 使用我是QQ打开TestLanuch的Test1Activity，然后按返回键退栈 
 
要解决这个问题有两种方式：

利用singleTask清除这个activity任务栈上面所有的activity特性

我们提供的分享页面始终是我们栈底的元素，只要他一启动就会清空任务栈内其他Activity，保证只有他一个实例。

android:taskAffinity=”要打开本应用的其他应用包名”

例如在本应用真就设置：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity </span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">".MainActivity"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:label</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"@string/app_name"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:taskAffinity</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"com.test.newlaunch"</span> ></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">action</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.action.MAIN"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">category</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">android:name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"android.intent.category.LAUNCHER"</span> /></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">intent-filter</span>></span> <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">activity</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

这样在Test1Activity启动的时候，如果com.test.newlaunch没启动就新建一个任务栈，如果com.test.newlaunch启动了就直接加入它的任务栈。

SingleInstance

单一实例模式，整个手机操作系统里面只有一个实例存在。不同的应用去打开这个activity 共享公用的同一个activity。他会运行在自己单独，独立的任务栈里面，并且任务栈里面只有他一个实例存在。应用场景：呼叫来电界面。这种模式的使用情况比较罕见，在Launcher中可能使用。或者你确定你需要使Activity只有一个实例。 
可以得出以下结论： 
1. 以singleInstance模式启动的Activity具有全局唯一性，即整个系统中只会存在一个这样的实例。 
2. 以singleInstance模式启动的Activity在整个系统中是单例的，如果在启动这样的Activiyt时，已经存在了一个实例，那么会把它所在的任务调度到前台，重用这个实例。 
3. 以singleInstance模式启动的Activity具有独占性，即它会独自占用一个任务，被他开启的任何activity都会运行在其他任务中。 
4. 被singleInstance模式的Activity开启的其他activity，能够在新的任务中启动，但不一定开启新的任务，也可能在已有的一个任务中开启。

换句话说，其实SingleInstance就是我们刚才分析的SingleTask中，分享Activity为栈底元素的情况。

代码下载地址