Android 深入理解Android中的自定义属性

转载请标明出处： 
http://blog.csdn.net/lmj623565791/article/details/45022631； 
本文出自:【张鸿洋的博客】

1、引言

对于自定义属性，大家肯定都不陌生，遵循以下几步，就可以实现：

1. 自定义一个CustomView(extends View )类
2. 编写values/attrs.xml，在其中编写styleable和item等标签元素
3. 在布局文件中CustomView使用自定义的属性（注意namespace）
4. 在CustomView的构造方法中通过TypedArray获取

ps:如果你对上述几个步骤不熟悉，建议先熟悉下，再继续~

那么，我有几个问题：

• 以上步骤是如何奏效的？
• styleable 的含义是什么？可以不写嘛？我自定义属性，我声明属性就好了，为什么一定要写个styleable呢？
• 如果系统中已经有了语义比较明确的属性，我可以直接使用嘛？
• 构造方法中的有个参数叫做AttributeSet 
  （eg: MyTextView(Context context, AttributeSet attrs) ）这个参数看名字就知道包含的是参数的数组，那么我能不能通过它去获取我的自定义属性呢？
• TypedArray是什么鬼？从哪冒出来的，就要我去使用？

恩，针对这几个问题，大家可以考虑下，如何回答呢？还是说：老子会背上述4个步骤就够了~~

2、常见的例子

接下来通过例子来回答上述问题，问题的回答顺序不定~~大家先看一个常见的例子，即上述几个步骤的代码化。

• 自定义属性的声明文件

<code class="language-xml hljs  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-pi" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><?xml version="1.0" encoding="utf-8"?></span><span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">resources</span>></span>    <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">declare-styleable</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"test"</span>></span>        <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">attr</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"text"</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">format</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"string"</span> /></span>        <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">attr</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"testAttr"</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">format</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"integer"</span> /></span>    <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">declare-styleable</span>></span><span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">resources</span>></span></code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">6</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">7</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">8</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">9</li></ul>

• 自定义View类

<code class="language-java hljs  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-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">package</span> com.example.test;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.Context;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.res.TypedArray;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.util.AttributeSet;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.util.Log;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.view.View;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="margin: 0px; padding: 0px; box-sizing: border-box;"><span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">MyTextView</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">View</span> {</span>    <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String TAG = MyTextView.class.getSimpleName();    <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box;">MyTextView</span>(Context context, AttributeSet attrs) {        <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(context, attrs);        TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.test);        String text = ta.getString(R.styleable.test_testAttr);        <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> textAttr = ta.getInteger(R.styleable.test_text, -<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);        Log.e(TAG, <span class="hljs-string" style="margin: 0px; padding: 0px; color: rgb(0, 136, 0); box-sizing: border-box;">"text = "</span> + text + <span class="hljs-string" style="margin: 0px; padding: 0px; color: rgb(0, 136, 0); box-sizing: border-box;">" , textAttr = "</span> + textAttr);        ta.recycle();    }}</code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">6</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">7</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">8</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">9</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">10</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">11</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">12</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">13</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">14</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">15</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">16</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">17</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">18</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">19</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">20</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">21</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">22</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">23</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">24</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">25</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">26</li></ul>

• 布局文件中使用

<code class="language-xml hljs  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="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">RelativeLayout</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">xmlns:android</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"http://schemas.android.com/apk/res/android"</span>    <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">xmlns:tools</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"http://schemas.android.com/tools"</span>    <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">xmlns:zhy</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"http://schemas.android.com/apk/res/com.example.test"</span>    <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">android:layout_width</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"match_parent"</span>    <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">android:layout_height</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"match_parent"</span> ></span>    <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">com.example.test.MyTextView</span>        <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">android:layout_width</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"100dp"</span>        <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">android:layout_height</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"200dp"</span>        <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">zhy:testAttr</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"520"</span>        <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">zhy:text</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"helloworld"</span> /></span><span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">RelativeLayout</span>></span></code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">6</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">7</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">8</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">9</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">10</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">11</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">12</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">13</li></ul>

ok，大家花3s扫一下，运行结果为：

<code class="language-java hljs  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;"> MyTextView: text = helloworld , textAttr = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">520</span></code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li></ul>

应该都不意外吧，注意下，我的styleable的name写的是test，所以说这里并不要求一定是自定义View的名字。

3、AttributeSet与TypedArray

下面考虑：

构造方法中的有个参数叫做AttributeSet（eg: MyTextView(Context context, AttributeSet attrs) ）这个参数看名字就知道包含的是参数的集合，那么我能不能通过它去获取我的自定义属性呢？

首先AttributeSet中的确保存的是该View声明的所有的属性，并且外面的确可以通过它去获取（自定义的）属性，怎么做呢？ 
其实看下AttributeSet的方法就明白了，下面看代码。

<code class="language-java hljs  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-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box;">MyTextView</span>(Context context, AttributeSet attrs) {        <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(context, attrs);        <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> count = attrs.getAttributeCount();        <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < count; i++) {            String attrName = attrs.getAttributeName(i);            String attrVal = attrs.getAttributeValue(i);            Log.e(TAG, <span class="hljs-string" style="margin: 0px; padding: 0px; color: rgb(0, 136, 0); box-sizing: border-box;">"attrName = "</span> + attrName + <span class="hljs-string" style="margin: 0px; padding: 0px; color: rgb(0, 136, 0); box-sizing: border-box;">" , attrVal = "</span> + attrVal);        }        <span class="hljs-comment" style="margin: 0px; padding: 0px; color: rgb(136, 0, 0); box-sizing: border-box;">// ==>use typedarray ...</span>    }</code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">6</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">7</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">8</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">9</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">10</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">11</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">12</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">13</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">14</li></ul>

输出：

<code class="language-java hljs  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;">MyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4136</span>): attrName = layout_width , attrVal = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">100.0</span>dipMyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4136</span>): attrName = layout_height , attrVal = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">200.0</span>dipMyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4136</span>): attrName = text , attrVal = helloworldMyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4136</span>): attrName = testAttr , attrVal = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">520</span></code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li></ul>

结合上面的布局文件，你发现了什么？ 
我擦，果然很神奇，真的获得所有的属性，恩，没错，通过AttributeSet可以获得布局文件中定义的所有属性的key和value（还有一些方法，自己去尝试），那么是不是说TypedArray这个鬼可以抛弃了呢？答案是：NO!。

现在关注下一个问题：

TypedArray是什么鬼？从哪冒出来的，就要我去使用？

我们简单修改下，布局文件中的MyTextView的属性。

<code class="language-xml hljs  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="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">com.example.test.MyTextView</span>        <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">android:layout_width</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"@dimen/dp100"</span>        <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">android:layout_height</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"@dimen/dp200"</span>        <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">zhy:testAttr</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"520"</span>        <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">zhy:text</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"@string/hello_world"</span> /></span></code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li></ul>

现在再次运行的结果是：

<code class="language-java hljs  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;">MyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4692</span>): attrName = layout_width , attrVal = @<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">2131165234</span>MyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4692</span>): attrName = layout_height , attrVal = @<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">2131165235</span>MyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4692</span>): attrName = text , attrVal = @<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">2131361809</span>MyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4692</span>): attrName = testAttr , attrVal = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">520</span>>>use typedarrayMyTextView(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">4692</span>): text = Hello world! , textAttr = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">520</span></code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">6</li></ul>

发现了什么？通过AttributeSet获取的值，如果是引用都变成了@+数字的字符串。你说，这玩意你能看懂么？那么你看看最后一行使用TypedArray获取的值，是不是瞬间明白了什么。

TypedArray其实是用来简化我们的工作的，比如上例，如果布局中的属性的值是引用类型（比如：@dimen/dp100），如果使用AttributeSet去获得最终的像素值，那么需要第一步拿到id，第二步再去解析id。而TypedArray正是帮我们简化了这个过程。

贴一下：如果通过AttributeSet获取最终的像素值的过程：

<code class="language-java hljs  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-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> widthDimensionId =  attrs.getAttributeResourceValue(<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, -<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);        Log.e(TAG, <span class="hljs-string" style="margin: 0px; padding: 0px; color: rgb(0, 136, 0); box-sizing: border-box;">"layout_width= "</span>+getResources().getDimension(widthDimensionId));</code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li></ul>

ok，现在别人问你TypedArray存在的意义，你就可以告诉他了。

4、declare-styleable

我们已经解决了两个问题，接下来，我们看看布局文件，我们有一个属性叫做：zhy:text。 
总所周知，系统提供了一个属性叫做：android:text，那么我觉得直接使用android:text更nice，这样的话，考虑问题：

如果系统中已经有了语义比较明确的属性，我可以直接使用嘛？

答案是可以的，怎么做呢？ 
直接在attrs.xml中使用android:text属性。

<code class="language-xml hljs  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="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">declare-styleable</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"test"</span>></span>        <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">attr</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"android:text"</span> /></span>        <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">attr</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"testAttr"</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">format</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"integer"</span> /></span>    <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">declare-styleable</span>></span></code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li></ul>

注意，这里我们是使用已经定义好的属性，不需要去添加format属性（注意声明和使用的区别，差别就是有没有format）。 
然后在类中这么获取：ta.getString(R.styleable.test_android_text);布局文件中直接android:text="@string/hello_world"即可。

这里提一下，系统中定义的属性，其实和我们自定义属性的方式类似，你可以在sdk/platforms/android-xx/data/res/values该目录下看到系统中定义的属性。然后你可以在系统提供的View（eg:TextView）的构造方法中发现TypedArray获取属性的代码（自己去看一下）。

ok，接下来，我在想，既然declare-styleable这个标签的name都能随便写，这么随意的话，那么考虑问题：

styleable 的含义是什么？可以不写嘛？我自定义属性，我声明属性就好了，为什么一定要写个styleable呢？

其实的确是可以不写的，怎么做呢？

• 首先删除declare-styleable的标签

那么现在的attrs.xml为：

<code class="language-xml hljs  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-pi" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><?xml version="1.0" encoding="utf-8"?></span><span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">resources</span>></span>    <span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">attr</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"testAttr"</span> <span class="hljs-attribute" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">format</span>=<span class="hljs-value" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 136, 0);">"integer"</span> /></span><span class="hljs-tag" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(0, 0, 136);">resources</span>></span></code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li></ul>

哟西，so清爽~ 
* MyTextView实现

<code class="language-java hljs  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-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">package</span> com.example.test;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.Context;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.content.res.TypedArray;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.util.AttributeSet;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.util.Log;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">import</span> android.view.View;<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="margin: 0px; padding: 0px; box-sizing: border-box;"><span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">MyTextView</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">View</span> {</span>    <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String TAG = MyTextView.class.getSimpleName();    <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[] mAttr = { android.R.attr.text, R.attr.testAttr };    <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ATTR_ANDROID_TEXT = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;    <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ATTR_TESTATTR = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;    <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box;">MyTextView</span>(Context context, AttributeSet attrs) {        <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(context, attrs);        <span class="hljs-comment" style="margin: 0px; padding: 0px; color: rgb(136, 0, 0); box-sizing: border-box;">// ==>use typedarray</span>        TypedArray ta = context.obtainStyledAttributes(attrs, mAttr);        String text = ta.getString(ATTR_ANDROID_TEXT);        <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> textAttr = ta.getInteger(ATTR_TESTATTR, -<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);        <span class="hljs-comment" style="margin: 0px; padding: 0px; color: rgb(136, 0, 0); box-sizing: border-box;">//输出 text = Hello world! , textAttr = 520</span>        Log.e(TAG, <span class="hljs-string" style="margin: 0px; padding: 0px; color: rgb(0, 136, 0); box-sizing: border-box;">"text = "</span> + text + <span class="hljs-string" style="margin: 0px; padding: 0px; color: rgb(0, 136, 0); box-sizing: border-box;">" , textAttr = "</span> + textAttr);        ta.recycle();    }}</code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">6</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">7</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">8</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">9</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">10</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">11</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">12</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">13</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">14</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">15</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">16</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">17</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">18</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">19</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">20</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">21</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">22</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">23</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">24</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">25</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">26</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">27</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">28</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">29</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">30</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">31</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">32</li></ul>

貌似多了些代码，可以看到我们声明了一个int数组，数组中的元素就是我们想要获取的attr的id。并且我们根据元素的在数组中的位置，定义了一些整形的常量代表其下标，然后通过TypedArray进行获取。 
可以看到，我们原本的：

<code class="language-xml hljs  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;">R.styleable.test => mAttrR.styleable.test_text => ATTR_ANDROID_TEXT(0)R.styleable.test_testAttr => ATTR_TESTATTR(1)</code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li></ul>

那么其实呢？android在其内部也会这么做，按照传统的写法，它会在R.java生成如下代码：

<code class="language-java hljs  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-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-class" style="margin: 0px; padding: 0px; box-sizing: border-box;"><span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">attr</span> {</span>    <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> testAttr=<span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">0x7f0100a9</span>;    }<span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-class" style="margin: 0px; padding: 0px; box-sizing: border-box;"><span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(102, 0, 102);">styleable</span> {</span>     <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> test_android_text = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;     <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span> test_testAttr = <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;      <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="margin: 0px; padding: 0px; color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[] test = {            <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">0x0101014f</span>, <span class="hljs-number" style="margin: 0px; padding: 0px; color: rgb(0, 102, 102); box-sizing: border-box;">0x7f0100a9</span>        };    }</code><ul class="pre-numbering" style="margin: 0px; padding: 6px 0px 40px; box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; 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="margin: 0px; padding: 0px 5px; box-sizing: border-box;">1</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">2</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">3</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">4</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">5</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">6</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">7</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">8</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">9</li><li style="margin: 0px; padding: 0px 5px; box-sizing: border-box;">10</li></ul>

ok，根据上述你应该发现了什么。styleale的出现系统可以为我们完成很多常量（int[]数组，下标常量）等的编写，简化我们的开发工作（想想如果一堆属性，自己编写常量，你得写成什么样的代码）。那么大家肯定还知道declare-styleable的name属性，一般情况下写的都是我们自定义View的类名。主要为了直观的表达，该declare-styleable的属性，都是改View所用的。

其实了解该原理是有用的，详见：Android 自定义控件 优雅实现元素间的分割线

ok，现在5个问题，回答了4个，第一个问题：

自定义属性的几个步骤是如何奏效的？

恩，上述以及基本涵盖了这个问题的答案，大家自己总结，所以：略。

总结下今天的博客。

• attrs.xml里面的declare-styleable以及item，android会根据其在R.java中生成一些常量方便我们使用(aapt干的)，本质上，我们可以不声明declare-styleable仅仅声明所需的属性即可。
• 我们在View的构造方法中，可以通过AttributeSet去获得自定义属性的值，但是比较麻烦，而TypedArray可以很方便的便于我们去获取。
• 我们在自定义View的时候，可以使用系统已经定义的属性。

近期的更新计划：自定义View的一些细节相关的Blog(重点会在交互上)，Android最佳实践相关的文章，framework相关的一些文章，敬请期待。

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