Android 如何获取当前Activity实例对象？

Android 如何获取当前Activity实例对象？

在项目开发中，遇到这么个情景，Activity是第三方部门的jar包，而我们需要当前界面用户输入的值 并且校验，jar包里面 并没有提供支持，然而这个jar包牵扯跨部门众多，更新困难。在短时间内只能靠我们自己 想办法获取当前屏幕的Activity 实例 对象，然后获取的View 遍历 到自己需要的值。

以上都是废话,直接看需求~。

获取当前屏幕Activity实例对象

网上很多说使用获取Task 名称，利用ActivityManager的runingtask 代码如下：
记得在加AndroidManifest.xml中增加权限

<uses-permission android:name="android.permission.GET_TASKS"/>

ActivityLifecycleCallbacks 是什么？

见名知意，Activity生命周期回调，Application通过此接口提供了一套回调方法，用于让开发者对Activity的生命周期事件进行集中处理。
但是这个要求API 14+ （Android 4.0+）以上使用，幸好我们这个最低支持，满足需求。

ActivityLifecycleCallbacks 怎么使用？

重写Application的onCreate()方法，或在Application的无参构造方法内，调用Application.registerActivityLifecycleCallbacks()方法，并实现ActivityLifecycleCallbacks接口

<code class="hljs java has-numbering"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onCreate</span>() {    <span class="hljs-keyword">super</span>.onCreate();    <span class="hljs-keyword">this</span>.registerActivityLifecycleCallbacks(<span class="hljs-keyword">new</span> ActivityLifecycleCallbacks() {      <span class="hljs-annotation">@Override</span>      <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onActivityStopped</span>(Activity activity) {          Logger.v(activity, <span class="hljs-string">"onActivityStopped"</span>);      }      <span class="hljs-annotation">@Override</span>      <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onActivityStarted</span>(Activity activity) {          Logger.v(activity, <span class="hljs-string">"onActivityStarted"</span>);      }      <span class="hljs-annotation">@Override</span>      <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onActivitySaveInstanceState</span>(Activity activity, Bundle outState) {          Logger.v(activity, <span class="hljs-string">"onActivitySaveInstanceState"</span>);      }      <span class="hljs-annotation">@Override</span>      <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onActivityResumed</span>(Activity activity) {          Logger.v(activity, <span class="hljs-string">"onActivityResumed"</span>);      }      <span class="hljs-annotation">@Override</span>      <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onActivityPaused</span>(Activity activity) {          Logger.v(activity, <span class="hljs-string">"onActivityPaused"</span>);      }      <span class="hljs-annotation">@Override</span>      <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onActivityDestroyed</span>(Activity activity) {          Logger.v(activity, <span class="hljs-string">"onActivityDestroyed"</span>);      }      <span class="hljs-annotation">@Override</span>      <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onActivityCreated</span>(Activity activity, Bundle savedInstanceState) {          Logger.v(activity, <span class="hljs-string">"onActivityCreated"</span>);      }    });  }; </code>

这样就能获取到activity的对象了。之前知道还有其他方法可以获取对象，没记住现在已经忘记了。如有大神发现，麻烦告诉小弟。~~谢谢

ActivityLifecycleCallbacks 为什么？

我们查看Application的源码，发现原来 ActivityLifecycleCallbacks 就是Application的内部类。

<code class="hljs java has-numbering"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Application</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">ContextWrapper</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">ComponentCallbacks2</span> {</span>    <span class="hljs-keyword">private</span> ArrayList<ComponentCallbacks> mComponentCallbacks =            <span class="hljs-keyword">new</span> ArrayList<ComponentCallbacks>();    <span class="hljs-keyword">private</span> ArrayList<ActivityLifecycleCallbacks> mActivityLifecycleCallbacks =            <span class="hljs-keyword">new</span> ArrayList<ActivityLifecycleCallbacks>();    <span class="hljs-keyword">private</span> ArrayList<OnProvideAssistDataListener> mAssistCallbacks = <span class="hljs-keyword">null</span>;    <span class="hljs-javadoc">/**<span class="hljs-javadoctag"> @hide</span> */</span>    <span class="hljs-keyword">public</span> LoadedApk mLoadedApk;    <span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">ActivityLifecycleCallbacks</span> {</span>        <span class="hljs-keyword">void</span> onActivityCreated(Activity activity, Bundle savedInstanceState);        <span class="hljs-keyword">void</span> onActivityStarted(Activity activity);        <span class="hljs-keyword">void</span> onActivityResumed(Activity activity);        <span class="hljs-keyword">void</span> onActivityPaused(Activity activity);        <span class="hljs-keyword">void</span> onActivityStopped(Activity activity);        <span class="hljs-keyword">void</span> onActivitySaveInstanceState(Activity activity, Bundle outState);        <span class="hljs-keyword">void</span> onActivityDestroyed(Activity activity);    }</code>

再来看是怎么回调的，这是内部API

// —————— Internal API ——————

<code class="hljs java has-numbering"><span class="hljs-javadoc">/**     *<span class="hljs-javadoctag"> @hide</span>     */</span>    <span class="hljs-comment">/* package */</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">void</span> attach(Context context) {        attachBaseContext(context);        mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;    }       <span class="hljs-comment">//调用onActivityCreated</span>    <span class="hljs-comment">/* package */</span> <span class="hljs-keyword">void</span> dispatchActivityCreated(Activity activity, Bundle savedInstanceState) {        Object[] callbacks = collectActivityLifecycleCallbacks();        <span class="hljs-keyword">if</span> (callbacks != <span class="hljs-keyword">null</span>) {            <span class="hljs-keyword">for</span> (<span class="hljs-keyword">int</span> i=<span class="hljs-number">0</span>; i<callbacks.length; i++) {                ((ActivityLifecycleCallbacks)callbacks[i]).onActivityCreated(activity,                        savedInstanceState);            }        }    }    <span class="hljs-comment">//调用onActivityStarted</span>    <span class="hljs-comment">/* package */</span> <span class="hljs-keyword">void</span> dispatchActivityStarted(Activity activity) {        Object[] callbacks = collectActivityLifecycleCallbacks();        <span class="hljs-keyword">if</span> (callbacks != <span class="hljs-keyword">null</span>) {            <span class="hljs-keyword">for</span> (<span class="hljs-keyword">int</span> i=<span class="hljs-number">0</span>; i<callbacks.length; i++) {                ((ActivityLifecycleCallbacks)callbacks[i]).onActivityStarted(activity);            }        }    }</code>

其他应用

我们还可以利用ActivityLifecycleCallbacks 做一些数据埋点，统计之类的应用，对其统一做处理。这样对减少Activity的代码入侵。尽量简化和模块化的注入生命周期方法。

 本文章转载自：http://blog.csdn.net/vfush/article/details/51483436