ionic 3-无法在http请求内创建警报

因此,我将本机HTTP cordova插件用于我的HTTP请求。但我似乎无法解决无法在onFail函数中创建警报的问题。还有其他人经历过吗?

错误显示:

Error in Error callbackId: CordovaHttpPlugin1608257770 : TypeError: Cannot 
read property 'alertCtrl' of undefined

下面是我如何构建代码的:

cordova.plugin.http.sendRequest('http://127.0.0.1:5000/api/login/', options, function(response) {

        try {   //onSuccess
            response.data = JSON.parse(response.data);

            localStorage.setItem('token', JSON.stringify(response.data.token));

          } catch(e) {
            console.error('JSON parsing error');
          }
        },  function(response) {    //onFail
            console.log('403');

            let alert = this.alerts.create({
                title: 'Error',
                subTitle: 'Username/password is invalid!',
                buttons: ['Dismiss']
            });
            alert.present();

        }
    );

我的构造函数是这样的:

constructor(public navCtrl: NavController,
            private alerts: AlertController, 
            private http: HTTP, 
            private store: Storage, 
            ) {}

是什么导致它不起作用?