Android AlertDialog 抢焦点的问题

当AlertDialog显示的时候，Activity的焦点被抢去，如何避免AlertDialog 被抢焦点呢？

                        dialog.setCanceledOnTouchOutside(true);
                        Window window = dialog.getWindow();
                        WindowManager.LayoutParams lp = window.getAttributes();
                        window.setGravity(Gravity.CENTER);
                        window.setFlags(WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE);
                        dialog.show();

完事。