sheishuoAPP/app/res/drawable/btn2_selector.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="false">
        <shape android:shape="rectangle">
            <corners android:radius="24dp" />
            <solid android:color="@color/colorPrimary" />
        </shape>
    </item>
    <item android:state_pressed="true" >
        <shape>
            <corners android:radius="24dp" />
            <solid android:width="3dp" android:color="@color/colorPrimaryDark" />
        </shape>
    </item>
</selector>