窗口类型2039的权限被拒绝

如何解决窗口类型2039的权限被拒绝

我尝试使用Windowmanager在来电屏幕中弹出一个窗口，I follow this second answer来实现它。但是，我得到了错误显示permission denied for window type 2039，这是什么类型的错误？该如何解决？

 protected void onIncomingCallStarted(Context ctx,String number,Date start) {
    super.onIncomingCallStarted(ctx,number,start);

    Toast.makeText(ctx,"Incoming: "+number,Toast.LENGTH_LONG).show();

    WindowManager wm = (WindowManager) ctx.getSystemService(Context.WINDOW_SERVICE);

    WindowManager.LayoutParams params = new WindowManager.LayoutParams(
            WindowManager.LayoutParams.MATCH_PARENT,WindowManager.LayoutParams.MATCH_PARENT,WindowManager.LayoutParams.TYPE_SYstem_ALERT |
            WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY,WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL |
                    WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,PixelFormat.TRANSPARENT);

    params.height = WindowManager.LayoutParams.MATCH_PARENT;
    params.width = WindowManager.LayoutParams.MATCH_PARENT;
    params.format = PixelFormat.TRANSLUCENT;

    params.gravity = Gravity.TOP;

    LinearLayout ly = new LinearLayout(ctx);
    ly.setBackgroundColor(Color.RED);
    ly.setorientation(LinearLayout.VERTICAL);

    wm.addView(ly,params);

}

我想做的功能是：来电时，来电屏幕上可以有一个添加新联系人的按钮或一个TextView以显示一些联系人信息。 怎么做？任何例子吗？预先感谢。