firebase - 在 firebase.auth().onAuthStateChanged 中使用 Provider 返回 undefined

Question

我尝试调用一个函数，它是 Provider 的一部分，但我注意到当调用在 firebase.auth().onAuthStateChanged函数内部时，所有提供程序都是未定义的。

@Ionic3.9.2 @cordova-8.1.2 (cordova-lib@8.1.1)

那是我的代码：

constructor(public global:global,public navCtrl: NavController, public navParams: NavParams, public app: App, public dataProvider: DataProvider,
        public loadingProvider: LoadingProvider, public alertProvider: AlertProvider, public alertCtrl: AlertController, public firebaseProvider: FirebaseProvider, public modalCtrl: ModalController) { }

    ionViewDidLoad() {
        console.log(this.dataProvider);




        firebase.auth().onAuthStateChanged(function (user) {
            if (user) {
                // User is signed in.
                console.log(user);
                this.currentUser=user;
                this.tab = "friends";
                this.title = "Friends";

                this.searchFriend = '';

                console.log(this.dataProvider); /*   -> undefined*/
                if (this.dataProvider.getRequests(this.currentUser != null)) {  /* the console return to me an error  :TypeError: Cannot read property 'getRequests' of undefined */
                    console.log(this.dataProvider.getRequests(this.currentUser));
                    // console.log(this.dataProvider.getRequests(firebase.auth().currentUser.uid));
                    console.log("if ");

                    // console.log(this.currentUser.uid);
                    console.log(this.currentUser);
                    this.dataProvider.getRequests(this.currentUser.uid).snapshotChanges().subscribe((requestsRes) => {
                        let requests = requestsRes.payload.val();
                        console.log(requests);
                        if (requests != null) {
                            if (requests.friendRequests != null && requests.friendRequests != undefined)
                                this.friendRequestCount = requests.friendRequests.length;
                            else this.friendRequestCount = 0
                        }
                        else this.friendRequestCount = 0;
                        console.log(this.friendRequestCount);
                    });

                    this.getFriends();
                }
            } else {
                // No user is signed in.
                console.log('no User');
            }
        });

我确信我错过了一些东西，并感谢一些帮助谢谢！

标签： firebaseionic-frameworkionic3firebase-authentication

Answer 1

好的，我找到了解决方案

解释：都是关于“this”关键字的

回调中的 this.dataProvider 与回调函数外的 this.dataProvider 不一样。

要在回调函数内外引用相同的this.dataProvider，只需要创建一个函数并将dataProvider作为参数传递即可。

constructor(public global:global,public navCtrl: NavController, public navParams: NavParams, public app: App, public dataProvider: DataProvider,
        public loadingProvider: LoadingProvider, public alertProvider: AlertProvider, public alertCtrl: AlertController, public firebaseProvider: FirebaseProvider, public modalCtrl: ModalController) { 
this.ionViewDidLoad(this.dataProvider); // <--- with this (mandatory)
}
    ionViewDidLoad(dataProvider: DataProvider) {
        console.log(dataProvider); // <-- defined with or without this
        firebase.auth().onAuthStateChanged(function (user) {
         .........

                console.log(dataProvider); /* without this  -> NOT undefined anymore :) */

       })