"TypeError: Kann Eigenschaft 'nav' von undefined nicht lesen" in Ionic

Question

Ich habe eine ähnliche Frage vor zwei Tagen aufgeworfen, aber dieses Mal bekomme ich den gleichen Fehler, wenn ich den Code in einem tatsächlichen Gerät oder Simulator ausführen. In einem normalen Browser funktioniert es gut.

Hier ist mein app.component.ts Code:

import { Component, ViewChild } from '@angular/core'; 
import { Platform } from 'ionic-angular'; 
import { StatusBar } from '@ionic-native/status-bar'; 
import { SplashScreen } from '@ionic-native/splash-screen'; 
import { HomePage } from '../pages/home/home'; 
import { LoginPage } from '../pages/login/login'; 
import {NativeStorage} from '@ionic-native/native-storage'; 
import { NavController } from 'ionic-angular'; 

@Component({ 
    templateUrl: 'app.html' 
}) 

export class MyApp { 
    rootPage:any = LoginPage; 
    @ViewChild('navApp') nav : NavController; 
    constructor(platform: Platform, statusBar: StatusBar, splashScreen: SplashScreen, private nativeStorage: NativeStorage,) { 
    platform.ready().then(() => { 
     this.nativeStorage.getItem('userExists').then((data)=>{ 
     this.nav.push(HomePage); 
     console.log(data.userExists); 
     },(error)=>{ 
     console.log("No Data in Local Storage"); 
      this.nav.push(LoginPage); 
     }) 

     statusBar.styleDefault(); 
     splashScreen.hide(); 
    }); 
    } 

} 

Das ist mein app.html

info

<ion-nav #navApp [root]="rootPage"></ion-nav> 

Dies ist meine Version

global packages: 

    @ionic/cli-utils : 1.2.0 
    Cordova CLI  : 7.0.1 
    Ionic CLI  : 3.2.0 

local packages: 

    @ionic/app-scripts    : 1.3.7 
    @ionic/cli-plugin-cordova  : 1.2.1 
    @ionic/cli-plugin-ionic-angular : 1.2.0 
    Cordova Platforms    : android 6.2.3 
    Ionic Framework     : ionic-angular 3.2.1 

System: 

    Node  : v6.10.2 
    OS   : Windows 10 
    Xcode  : not installed 
    ios-deploy : not installed 
    ios-sim : not installed 

Package.json ist:

{ 
    "name": "myapp", 
    "version": "0.0.1", 
    "author": "Ionic Framework", 
    "homepage": "http://ionicframework.com/", 
    "private": true, 
    "scripts": { 
     "clean": "ionic-app-scripts clean", 
     "build": "ionic-app-scripts build", 
     "lint": "ionic-app-scripts lint", 
     "ionic:build": "ionic-app-scripts build", 
     "ionic:serve": "ionic-app-scripts serve" 
    }, 
    "dependencies": { 
     "@angular/common": "4.1.0", 
     "@angular/compiler": "4.1.0", 
     "@angular/compiler-cli": "4.1.0", 
     "@angular/core": "4.1.0", 
     "@angular/forms": "4.1.0", 
     "@angular/http": "4.1.0", 
     "@angular/platform-browser": "4.1.0", 
     "@angular/platform-browser-dynamic": "4.1.0", 
     "@ionic-native/core": "3.7.0", 
     "@ionic-native/facebook": "^3.10.2", 
     "@ionic-native/native-storage": "^3.10.3", 
     "@ionic-native/splash-screen": "3.7.0", 
     "@ionic-native/status-bar": "3.7.0", 
     "@ionic/storage": "2.0.1", 
     "cordova-android": "^6.2.3", 
     "cordova-plugin-console": "^1.0.5", 
     "cordova-plugin-device": "^1.1.4", 
     "cordova-plugin-facebook4": "^1.9.0", 
     "cordova-plugin-nativestorage": "^2.2.2", 
     "cordova-plugin-splashscreen": "^4.0.3", 
     "cordova-plugin-statusbar": "^2.2.2", 
     "cordova-plugin-whitelist": "^1.3.1", 
     "ionic-angular": "3.2.1", 
     "ionic-native": "^2.5.1", 
     "ionic-plugin-keyboard": "^2.2.1", 
     "ionicons": "3.0.0", 
     "rxjs": "5.1.1", 
     "sw-toolbox": "3.6.0", 
     "zone.js": "0.8.10" 
    }, 
    "devDependencies": { 
     "@ionic/app-scripts": "1.3.7", 
     "@ionic/cli-plugin-cordova": "^1.2.1", 
     "@ionic/cli-plugin-ionic-angular": "^1.2.0", 
     "typescript": "2.2.1" 
    }, 
    "description": "An Ionic project", 
    "cordova": { 
     "plugins": { 
      "cordova-plugin-console": {}, 
      "cordova-plugin-device": {}, 
      "cordova-plugin-splashscreen": {}, 
      "cordova-plugin-statusbar": {}, 
      "cordova-plugin-whitelist": {}, 
      "ionic-plugin-keyboard": {}, 
      "cordova-plugin-facebook4": { 
       "APP_ID": "305938313175123", 
       "APP_NAME": "myapp" 
      }, 
      "cordova-plugin-nativestorage": {} 
     }, 
     "platforms": [ 
      "android" 
     ] 
    } 
} 

Answer 1

Aktualisierung auf die neueste ionische Version 3.3.0 löste das Problem!

Answer 2

Warum ändern Sie nicht einfach den Wert von rootPage, anstatt einen Push zu machen?

Sie haben die Variable

rootPage:any = LoginPage; 

So standardmäßig Ihre Homepage Loginpage sein wird. Wenn Sie in Ihrem local überprüfen, ob der Spitzname existiert, stattdessen eine Seite gedrückt wird, verwenden

this.rootPage = NameofYourPageHere. 

Das sollte funktionieren.