<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/><!--这行代码必须存在，否则点击不了系统设置中的按钮-->
  <uses-permission android:name="android.permission.SYSTEM_OVERLAY_WINDOW" />

 private void checkMyPermission() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
      if (!Settings.canDrawOverlays(this)) {
        Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
            Uri.parse("package:" + getPackageName()));
        startActivityForResult(intent, 1);
      }
    }
  }
 
  @Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == 1) {
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        if (Settings.canDrawOverlays(this)) {
          Toast.makeText(this, "授权成功", Toast.LENGTH_SHORT).show();
        }else {
          // SYSTEM_ALERT_WINDOW permission not granted...
          Toast.makeText(this, "未被授予权限，相关功能不可用", Toast.LENGTH_SHORT).show();
        }
      }
    }
  }

//在 Service 中创建全局变量 mHandler
  private Handler mHandler;
//在 Service 生命周期方法 onCreate() 中初始化 mHandler
  mHandler = new Handler(Looper.getMainLooper());
//在子线程中想要 Toast 的地方添加如下
  mHandler.post(new Runnable() {
          @Override
          public void run() {
            //show dialog
            justShowDialog();
          }
        });
 
  private void justShowDialog() {
    AlertDialog.Builder builder = new AlertDialog.Builder(getApplicationContext())
        .setIcon(android.R.drawable.ic_dialog_info)
        .setTitle("service中弹出Dialog了")
        .setMessage("是否关闭dialog？")
        .setPositiveButton("确定",
            new DialogInterface.OnClickListener() {
              public void onClick(DialogInterface dialog,
                        int whichButton) {
              }
            })
        .setNegativeButton("取消",
            new DialogInterface.OnClickListener() {
              public void onClick(DialogInterface dialog,
                        int whichButton) {
              }
            });
    //下面这行代码放到子线程中会 Can't create handler inside thread that has not called Looper.prepare()
    AlertDialog dialog = builder.create();
    //设置点击其他地方不可取消此 Dialog
    dialog.setCancelable(false);
    dialog.setCanceledOnTouchOutside(false);
    //8.0系统加强后台管理，禁止在其他应用和窗口弹提醒弹窗，如果要弹，必须使用TYPE_APPLICATION_OVERLAY，否则弹不出
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
      dialog.getWindow().setType((WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY));
    }else {
      dialog.getWindow().setType((WindowManager.LayoutParams.TYPE_SYSTEM_ALERT));
    }
    dialog.show();
  }