效果如下 (第二个按钮)

所有的按钮均在一个带有android:stretchColumns="*"的TableLayout的多个TableRow下。下帖代码。

main.xml

<Button
    android:id="@+id/button2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@drawable/gray_bg"
    android:text="@string/calculator_multiply"
/>

gray_bg.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
    <corners android:radius="5dp"/>
    <item android:drawable="@drawable/gray_default" android:state_pressed="false"></item>
    <item android:drawable="@drawable/gray_active" android:state_pressed="true"></item>
</selector>

gray_default.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >
    <corners android:radius="5dp"/>
    <solid android:color="@color/gray_default"/>
</shape>

gray_active.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >
    <corners android:radius="5dp"/>
    <solid android:color="@color/gray_active"/>
</shape>