问在使用BarcodeScanner时，我的离子应用程序出现了以下错误

EN

<ion-header class="toolbar">
  <ion-navbar>
    <ion-title>Scan</ion-title>
  </ion-navbar>

</ion-header>

<ion-content padding class="Scan">
  <div class="row">
    <div class="col">
      <h2>Scan your QR Code Here</h2>
    </div>
    <div class="col">
      <h3>{{eventTitle}}</h3>
    </div>
  </div>
  <button ion-button block color="secondary" class="Scan-button" (click)="scanQR()" [disabled]="loading">{{buttonText}}</button>
</ion-content>

import { Component } from '@angular/core';
import {Platform} from "ionic-angular";
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import { SplashScreen } from '@ionic-native/splash-screen';
import { StatusBar } from '@ionic-native/status-bar';
import { ToastController } from 'ionic-angular';
import { BarcodeScanner, BarcodeScannerOptions } from '@ionic-native/barcode-scanner/ngx';


/**
 * Generated class for the MenuPage page.
 *
 * See https://ionicframework.com/docs/components/#navigation for more info on
 * Ionic pages and navigation.
 */

@IonicPage()
@Component({
  selector: 'page-menu',
  templateUrl: 'menu.html',
})
export class MenuPage {

  public scannedText: string;
  public buttonText: string;
  public loading: boolean;
  private eventId: number;
  public eventTitle: string;

  num: string;

  // @ts-ignore
  constructor(private _nav: NavController,
              private _navParams: NavParams,
              private _barcodeScanner: BarcodeScanner) {



  }
  ionViewDidLoad() {
    this.eventId = this._navParams.get('eventId');
    this.eventTitle = this._navParams.get('eventTitle');

    this.buttonText = "Scan";
    this.loading = false;
  }

  public scanQR() {
    this.buttonText = "Loading..";
    this.loading = true;

    this._barcodeScanner.scan().then((barcodeData) => {
      if (barcodeData.cancelled) {
        console.log("User cancelled the action!");
        this.buttonText = "Scan";
        this.loading = false;
        return false;
      }
      console.log("Scanned successfully!");
      console.log(barcodeData);
      this.goToResult(barcodeData);
    }, (err) => {
      console.log(err);
    });
  }

  private goToResult(barcodeData) {
    this._nav.push(ScanResultPage, {
      scannedText: barcodeData.text
    });
  }
}

import { BrowserModule } from '@angular/platform-browser';
import { ErrorHandler, NgModule } from '@angular/core';
import { IonicApp, IonicErrorHandler, IonicModule } from 'ionic-angular';
import { SplashScreen } from '@ionic-native/splash-screen';
import { StatusBar } from '@ionic-native/status-bar';
import { MyApp } from './app.component';
import { HomePage } from '../pages/home/home';
import {MenuPage} from "../pages/menu/menu";
import { BarcodeScanner } from '@ionic-native/barcode-scanner/ngx';
import { HttpClientModule } from '@angular/common/http';

import { FormsModule } from '@angular/forms';
import {HttpModule} from "@angular/http";


// @ts-ignore
@NgModule({
  declarations: [
    MyApp,
    HomePage,
    MenuPage
  ],
  imports: [
    BrowserModule, HttpClientModule,
    IonicModule.forRoot(MyApp),
    HttpModule
  ],
  bootstrap: [IonicApp],
  entryComponents: [
    MyApp,
    HomePage,
    MenuPage
  ],
  providers: [
    StatusBar,
    SplashScreen,
    BarcodeScanner,
    {provide: ErrorHandler, useClass: IonicErrorHandler}




  ]


})
export class AppModule {}