Question

我尝试调用提供程序中一部分的函数，但是我注意到调用位于firebase.auth().onAuthStateChanged函数内部，所有提供程序都未定义。

@ 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');
            }
        });

我确信我会错过一些东西，并感谢您的帮助！

Answer 1

好，我找到了解决方法

说明：全部与“ this”关键字有关

回调函数中的

this.dataProvider与回调函数外部的this.dataProvider不同。

要在回调函数的内部和外部引用相同的this.dataProvider，您只需创建一个函数并将dataProvider作为参数传递。

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 :) */

       })

使用Provider内部firebase.auth（）。onAuthStateChanged返回未定义

1 个答案: