创造一个窗口置于顶层,覆盖Activity

创建一个窗口置于顶层,覆盖Activity
WindowManager mWm = (WindowManager)getSystemService(Context.WINDOW_SERVICE);
        Button view = new Button(this);
        view.setText("window manager test!");
        WindowManager.LayoutParams mParams = new WindowManager.LayoutParams();
        mWm.addView(view, mParams);