android 兑现button的背景改变

<?xml version="1.0" encoding="UTF-8"?><selector xmlns:android="http://schemas.android.com/apk/res/android">	<item android:state_focused="true" android:state_pressed="true"		android:drawable="@drawable/button_bg_down" />	<item android:state_focused="false" android:state_pressed="true"		android:drawable="@drawable/button_bg_down" />	<item android:state_focused="true" android:drawable="@drawable/button_bg_down" />	<item android:state_focused="false" android:drawable="@drawable/button_bg" /></selector>将这个xml文件放在存放存放图片的folder中(menu_button.xml)在布局xml文件中定义button时 ，这样<Button				android:id="@+id/start_game"				android:layout_width="220dip"				android:layout_height="wrap_content"				android:layout_gravity="center"				android:text="Start"				android:textColor="#FF292066"				android:textSize="17sp"				android:padding="8dip"				android:background="@drawable/menu_button"				android:layout_marginBottom="3dip" />在android:backgound属性中定义为刚才的xml文件名，这样当点击button时， button的背景就会动态变化。