popupWindow點擊外面消失

1.

View view = inflater.inflate(R.layout.popwindowdemo, null);
				final PopupWindow pop = new PopupWindow(view, 600, 800);
				pop.setBackgroundDrawable(new BitmapDrawable());
				pop.setFocusable(true);// 如果不加這個，Grid不會響應ItemClick
				pop.showAtLocation(layout, Gravity.CENTER, 0, 0);

這裏我提一點，點擊外部消失關鍵性一步是pop.setBackgroundDrawable(new BitmapDrawable());

我之前把這句話寫在pop.showAtLocation()之後;也無法顯示