用shape结合selector实现点击效果

<span style="font-family:Arial, Helvetica, sans-serif;font-size:18px;background-color: rgb(255, 255, 255);">有时候美工为了省事，不给我们图片，没办法，也不能得罪美工呀，但是我们可以用颜色实现我们的点击效果呀！</span>

<span style="font-family: Arial, Helvetica, sans-serif;"><?xml version="1.0" encoding="UTF-8"?></span>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >

    <gradient
        android:angle="90"
        android:endColor="#ffff99"
        android:startColor="#ffff99" />

    <corners android:radius="20dp" />

</shape>

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

    <gradient
        android:angle="90"
        android:endColor="#cc3935"
        android:startColor="#cc3935" />

    <corners android:radius="20dp" />

</shape>

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

    <item android:drawable="@drawable/red_shape" android:state_pressed="true"/>
    <item android:drawable="@drawable/gray_shape"/>

</selector>