安卓在适配器里面设置屏幕透明度

把Activity对象作为参数传过去啊。。在adapter的构造方法里面加上Activity参数啊
getWindow()是Activity类的方法。

/**
 * Retrieve the current {@link android.view.Window} for the activity.
 * This can be used to directly access parts of the Window API that
 * are not available through Activity/Screen.
 *
 * @return Window The current window, or null if the activity is not
 *         visual.
 */
public Window getWindow() {
    return mWindow;
}

例子：
Class TestActivity:
...
TestAdapter adapter = new TestAdapter(this);
...

Class TestAdapter:
...
Activity mActivity;
TestAdapter(Activity activity){
mActivity = activity;
}
...
public void backgroundAlpha(float bgAlpha)
{
WindowManager.LayoutParams lp =mActivity.getWindow().getAttributes();
lp.alpha = bgAlpha; //0.0-1.0
getWindow().setAttributes(lp);
}
...