Android で透明度と暗さを設定する 3 つの方法についての簡単な説明

android:background="@android:color/transparent"

//半透明
<Button android:background="#e0000000" /> 
//透明
<Button android:background="#00000000" />

View v = findViewById(R.id.content);//找到你要设透明背景的layout 的id 
v.getBackground().setAlpha(100);//0~255透明度值

WindowManager.LayoutParams lp=getWindow().getAttributes();
lp.alpha=0.3f;
getWindow().setAttributes(lp);

WindowManager.LayoutParams lp=getWindow().getAttributes();
lp.dimAmount=0.5f;
getWindow().setAttributes(lp);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);

<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>

<?xml version="1.0" encoding="utf-8"?>  
<resources>  
  <color name="transparent_background">#50000000</color>  
</resources>  
//注意：
//color.xml的#5000000前两位是透明的效果参数从00--99（透明--不怎么透明），
//后6位是颜色的设置

<activity 
android:name=".TransparentActivity" 
android:theme="@style/Transparent">  
</activity>

public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setTheme(R.style.Transparent);   
        setContentView(R.layout.transparent);  
}