/**
* 調整窗口的透明度
* @param from>=0&&from<=1.0f
* @param to>=0&&to<=1.0f
*
* */
private void dimBackground(final float from, final float to) {
final Window window = getWindow();
ValueAnimator valueAnimator = ValueAnimator.ofFloat(from, to);
valueAnimator.setDuration(500);
valueAnimator.addUpdateListener(new AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
WindowManager.LayoutParams params = window.getAttributes();
params.alpha = (Float) animation.getAnimatedValue();
window.setAttributes(params);
}
});

    valueAnimator.start();
}

然后這樣調用：

/** 窗口背景變暗*/
dimBackground(1.0f,0.5f);


/** 窗口背景變亮*/
dimBackground(0.5f,1.0f);