Android中的Drawable资源—— StateListDrawable

这种使用xml来定义图片的方式在buttion中经常使用，它会根据状态来显示不同的图片资源。

存放位置：
res/drawable/

使用方式：
在Java文件中：R.drawable.filename

例如：

Resources res = getResources();Drawable drawable = res.getDrawable(R.drawable.myimage);

在xml布局文件中：@[package:]drawable/filename

例如：

<Button    android:layout_height="wrap_content"    android:layout_width="wrap_content"    android:background="@drawable/myninepatch" />

语法：

<?xml version="1.0" encoding="utf-8"?><selector xmlns:android="http://schemas.android.com/apk/res/android"    android:constantSize=["true" | "false"]    android:dither=["true" | "false"]    android:variablePadding=["true" | "false"] >    <item        android:drawable="@[package:]drawable/drawable_resource"        android:state_pressed=["true" | "false"]        android:state_focused=["true" | "false"]        android:state_hovered=["true" | "false"]        android:state_selected=["true" | "false"]        android:state_checkable=["true" | "false"]        android:state_checked=["true" | "false"]        android:state_enabled=["true" | "false"]        android:state_activated=["true" | "false"]        android:state_window_focused=["true" | "false"] /></selector>

例如：

<?xml version="1.0" encoding="utf-8" ?>     <selector xmlns:android="http://schemas.android.com/apk/res/android">     <!-- 触摸时并且当前窗口处于交互状态 -->      <item android:state_pressed="true" android:state_window_focused="true" android:drawable= "@drawable/pic1" />    <!--  触摸时并且没有获得焦点状态 -->      <item android:state_pressed="true" android:state_focused="false" android:drawable="@drawable/pic2" />      <!--选中时的图片背景-->      <item android:state_selected="true" android:drawable="@drawable/pic3" />       <!--获得焦点时的图片背景-->      <item android:state_focused="true" android:drawable="@drawable/pic4" />      <!-- 窗口没有处于交互时的背景图片 -->      <item android:drawable="@drawable/pic5" />   </selector>  

<Button    android:layout_height="wrap_content"    android:layout_width="wrap_content"    android:background="@drawable/button" />

另外，需要说的是，上面定义的这个xml会被相应的解析为StateListDrawable对象，所以我们也可以使用代码来进行实现。

//初始化一个空对象  StateListDrawable stalistDrawable = new StateListDrawable();  //获取对应的属性值 Android框架自带的属性 attr  int pressed = android.R.attr.state_pressed;  int window_focused = android.R.attr.state_window_focused;  int focused = android.R.attr.state_focused;  int selected = android.R.attr.state_selected;  stalistDrawable.addState(new int []{pressed , window_focused}, getResources().getDrawable(R.drawable.pic1));  stalistDrawable.addState(new int []{pressed , -focused}, getResources().getDrawable(R.drawable.pic2);  stalistDrawable.addState(new int []{selected }, getResources().getDrawable(R.drawable.pic3);  stalistDrawable.addState(new int []{focused }, getResources().getDrawable(R.drawable.pic4);  //没有任何状态时显示的图片，我们给它设置我空集合  stalistDrawable.addState(new int []{}, getResources().getDrawable(R.drawable.pic5); 

上面的“-”负号表示对应的属性值为false

https://developer.android.com/guide/topics/resources/drawable-resource.html#StateList

https://developer.android.com/reference/android/graphics/drawable/StateListDrawable.html

http://blog.csdn.net/qinjuning/article/details/7474827