android Activity 半透明效果

1.
res/values/styles.xml 

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <style name="Transparent">
    	<item name="android:windowBackground">@color/transparent_background</item>  
    	<item name="android:windowNoTitle">true</item> 
    	<item name="android:windowIsTranslucent">true</item> 
    	<item name="android:windowAnimationStyle">@+android:style/Animation.Translucent</item>
    </style>
</resources>

2.
res/values/colors.xml 

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="transparent_background">#50000000</color>    
</resources>

3.在setContentView(R.layout.main);之前setTheme(R.style.Transparent);