复合状态样式

        <Button 
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="下一步"
            android:background="@drawable/button_selector"   注：如果@android:drawable/表示使用系统样式，@drawable/            表示使用自建drawable目录下的样式；
            />

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
   
    <item android:state_pressed="true" 
        android:drawable="@drawable/function_greenbutton_pressed" />
    <item android:state_focused="true"
        android:drawable="@drawable/function_greenbutton_pressed" />
    <item
         android:drawable="@drawable/function_greenbutton_normal" />
</selector>