Android学习笔记之Button的点击事件切换点击图片

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="184dp"
        android:background="@drawable/button_selector" />

</RelativeLayout>

android:background="@drawable/button_selector"

（2）在res文件夹下创建drawable文件夹，创建一个selector文件

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:drawable="@drawable/q" android:state_pressed="true"></item>
    <item android:drawable="@drawable/w" android:state_focused="true"></item>
    <item android:drawable="@drawable/e"></item>

</selector>