令牌的值在函数之间为空

Question

我正在使用带有来自https://github.com/fechanique/cordova-plugin-fcm 的cordova-plugin-fcm 插件的ionic 2

我在将令牌值分配给 deviceId 时遇到问题，console.log 在调用中正确显示该值，但在外部返回 null

代码如下：

declare var FCMPlugin;

@Component({
  templateUrl: `app.template.html`
})
export class MyApp {
  @ViewChild(Nav) nav: Nav;
  public deviceId: any;


  appPages: PageObj[] = [
    { title: 'Home', component: HomePage, icon: 'home' },
    { title: 'Profile', component: UserProfilePage, icon: 'calendar' },
    { title: 'Give Feedback', component: FeedbackPage, icon: 'calendar' },
  ];

  rootPage: any;
  TutorialPage: TutorialPage;

  constructor(platform: Platform,
    public menu: MenuController,
    private actionSheetCtrl: ActionSheetController,
    public authService: AuthService,
    public dataService: DataService) {

    platform.ready().then(() => {
      // Okay, so the platform is ready and our plugins are available.
      // Here you can do any higher level native things you might need.
      StatusBar.styleDefault();
      Splashscreen.hide();

      FCMPlugin.getToken(
        function (token) {
          console.log('device token is ' + token);
           var deviceId = token;
          console.log('value of id is' + deviceId);
        },
        function (err) {
          console.log('error retrieving token: ' + err);
        }
      );
    });
  }

  ngOnInit() {
    var self = this;
    this.authService.onAuthStateChanged(function (user) {
      if (user === null) {
        self.nav.setRoot(TutorialPage);
      }
    });
  }

  ngAfterViewInit() {
        var self = this;
    this.authService.onAuthStateChanged(function (user) {
      if (user === null) {
        self.menu.close();
        self.nav.setRoot(TutorialPage);
      } else {
        console.log("device token upon login is" + this.deviceId);
        let uid = self.authService.getLoggedInUser().uid;
        console.log("uid at login is " + uid);
        self.dataService.setDeviceToken(uid, this.deviceId);
      }
    });

  }

deviceId 的值在 ngAfterViewInit 中显示为 null

终于开始工作了：----

有效的编辑代码是：

declare var FCMPlugin;

@Component({
  templateUrl: `app.template.html`
})
export class MyApp {
  @ViewChild(Nav) nav: Nav;
  public deviceId: any;


  appPages: PageObj[] = [
    { title: 'Home', component: HomePage, icon: 'home' },
    { title: 'Profile', component: UserProfilePage, icon: 'calendar' },
    { title: 'Give Feedback', component: FeedbackPage, icon: 'calendar' },
  ];

  rootPage: any;
  TutorialPage: TutorialPage;

  constructor(platform: Platform,
    public menu: MenuController,
    private actionSheetCtrl: ActionSheetController,
    public authService: AuthService,
    public dataService: DataService) {

    platform.ready().then(() => {
      // Okay, so the platform is ready and our plugins are available.
      // Here you can do any higher level native things you might need.
      StatusBar.styleDefault();
      Splashscreen.hide();

      FCMPlugin.getToken(
        token => {
          var self = this;
          console.log('device token is ' + token);
          let devicetoken = token;
          console.log('value of id is' + devicetoken);
          self.deviceId = devicetoken;

        },
        function (err) {
          console.log('error retrieving token: ' + err);
        }
      );
    });
  }

  ngOnInit() {
    var self = this;
    this.authService.onAuthStateChanged(function (user) {
      if (user === null) {
        self.nav.setRoot(TutorialPage);
      }
    });
  }

  ngAfterViewInit() {
    var self = this;
    this.authService.onAuthStateChanged(function (user) {
      if (user === null) {
        self.menu.close();
        self.nav.setRoot(TutorialPage);
      } else {
        console.log("device token upon login is" + self.deviceId);
        let uid = self.authService.getLoggedInUser().uid;
        console.log("uid at login is " + uid);
        self.dataService.setDeviceToken(uid, self.deviceId);
      }
    });

  }

Answer 1

第一次使用'deviceId'变量是在函数中声明的局部变量。

“deviceId”的第二个用途是 MyApp 实例（对象）中的一个字段，并且从未分配过。

改为：

FCMPlugin.getToken(
    token => {
      console.log('device token is ' + token);
       var deviceId = token;
      console.log('value of id is' + deviceId);
       this.deviceId = token;
    },
    function (err) {
      console.log('error retrieving token: ' + err);
    }
  );

还要确保从实例中检索到 deviceId，因此在回调函数 onAuthStateChanged 中，使用 self.deviceId 而不是 this.deviceId