琢磨了老半天，試了一下網上說的一種方法，我發現不行，這種方法是這樣的：

1.首先註冊靜態廣播

2.在清單中新增許可權

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

3.然後在show()之前設定Dialog型別為TYPE_SYSTEM_ALERT

alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);

然後發現還是不行。這就鬱悶啦！網上有人說用動態註冊方式可以實現在廣播接收者中彈出對話方塊，於是便試了一下，果然可以

首先開始註冊廣播，並給廣播訊息

private BroadcastReceiver broadcastReceiver;

broadcastReceiver=new tipsBroadReciver();
                IntentFilter intentFilter=new IntentFilter();
                intentFilter.addAction(ACTION);
                context.registerReceiver(broadcastReceiver,intentFilter);
                Intent intent=new Intent();
                intent.setAction(ACTION);
                intent.putExtra("state","1");
                context.sendBroadcast(intent);
 

 String state=intent.getExtras().getString("state");
        AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(context);
        dialogBuilder.setTitle("提示");
        if(state.equals("1")){
            text="沒有查詢到該好友";
        }
        dialogBuilder.setMessage(text);
        dialogBuilder.setCancelable(false);
        dialogBuilder.setPositiveButton("確定", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                context.unregisterReceiver(tipsBroadReciver.this);
            }
        });
        AlertDialog alertDialog = dialogBuilder.create();
        alertDialog.show();