function - 无法从 Ionic 中的 Toast 中读取属性“未定义”的“创建”

Question

我有这个代码：

import { Component } from '@angular/core';
import {NavController } from 'ionic-angular';
import * as firebase from 'firebase';
import firebase_admin from 'firebase';
import {LoginPage} from '../login/login';
import { RegisterPage } from '../register/register';
import { Diagnostic } from '@ionic-native/diagnostic';
import { ToastController } from 'ionic-angular';


@Component({
  selector: 'page-home',
  templateUrl: 'home.html'
})

export class HomePage {
  static get parameters() {
    return [[NavController]];
}
constructor(public navCtrl: NavController, public diagnostic: Diagnostic, public toastCtrl: ToastController) {
  this.navCtrl = navCtrl;
  this.toastCtrl = toastCtrl;

  }

openAddPage() {
  let successCallback = (isAvailable) => {   this.navCtrl.push(LoginPage)
  };
  let toast = this.toastCtrl.create({
    message: 'Test',
    duration: 3000,
    position: 'top'
  });
  this.diagnostic.isLocationAvailable().then(successCallback).catch(toast.present);

}



}

当我单击 html 文件中的登录按钮时，它会运行 (openAddPage)。当我这样做时，我收到以下错误：

TypeError：无法读取未定义的属性“创建”

问题是什么？