当sdk > 21,PopupWindow在标题栏没有办法遮罩
有两种方法：
方法1：
popupWindow.setClippingEnabled(false);
方法2：
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
try {
Field mLayoutInScreen = PopupWindow.class.getDeclaredField("mLayoutInScreen");
mLayoutInScreen.setAccessible(true);
mLayoutInScreen.set(popupWindow, true);
} catch (NoSuchFieldException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
