android的xml中怎么实现按钮按下去变颜色

//第一个例子
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:state_pressed="true" android:color="@color/baise"/>
  <item android:state_pressed="false" android:color="@color/heise"/>
</selector>

//第二个例子
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_pressed="true">
    <shape android:shape="rectangle">
        <solid android:color="@color/greencolor"/>
    </shape>
</item>

</selector>

//第三个例子
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="true">
        <shape android:shape="rectangle">
            <solid android:color="@color/greencolor"/>
            <corners android:radius="8dp"/>
            <padding android:bottom="0dp" android:top="0dp"/>

        </shape>
    </item>
    <item android:state_pressed="false">
        <shape android:shape="rectangle">
            <solid android:color="@color/graycolor"/>
            <padding android:bottom="0dp" android:top="0dp"/>
            <corners android:radius="8dp"/>
        </shape>
    </item>

</selector>