错误:属性'getChildren'在类型'数据快照'

Question

。。。它在文件P:中是这样做的

Iimport * as firebase from "firebase";位于文件顶部。uid获取函数起作用。出于某种原因，它不喜欢for循环的语法。。。

我还尝试了语法：for (DataSnapshot child : parent.getChildren()) { }，然后编译器告诉我在for循环开始的行中应该有分号。

getMessages() {
return new Promise(function (resolve) {
return firebase.auth().onAuthStateChanged(function (user) {
if (user) {
resolve(user.uid);
}
});
}).then((result) => {
return firebase.database().ref('mailboxes/' + result).once('value').then((snapshot) => {
let messageArray;
for (let snap of snapshot.getChildren()) {
messageArray.push(snap.val());
console.log('snapshot key:' + snap.key);
console.log('snapshot val:' + snap.val());
};
return messageArray;
});
});
}

Answer 1

您需要使用订阅来监视更改。使用AngularFire监视他们何时登录并获取UID(假设您在Firebase中使用身份验证登录，以便使用UID作为树路径保存所有数据

import { AngularFirestore } from 'angularfire2/firestore';
import { AngularFireDatabase, AngularFireList } from 'angularfire2/database';
import { AngularFireAuth } from 'angularfire2/auth';
import { switchMap, map } from 'rxjs/operators';
import { Observable,  pipe } from 'rxjs';
import { Observable, Subscription } from 'rxjs';
import firebase as firebase from 'firebase/app';
private myOAuthSubscription: Subscription;
private myDatasubscription: Subscription;    
public userloggedin:boolean = false;
public uid:string = '';
public this.items:any = [];
constructor(
public _DB: AngularFireDatabase,
public _afAuth: AngularFireAuth,
) {

try {
this.myOAuthSubscription = this._afAuth.authState.subscribe(user => {
if (user && user.uid) {
console.log('loggedin = true');
this.userloggedin = true;
this.uid = String(user.uid);
this.funDoDB():
} else {
console.log('loggedin = false');
this.userloggedin = true;
this.uid = '';
}
});
} catch (e) {
console.error("fbData_subscription", e);
}

}
ngOnDestroy() {
this.myOAuthSubscription.unsubscribe();
this.myDatasubscription.unsubscribe();
}

private funDoDB(){
if(this.userloggedin == true){
try {
//subscription using AngulaFire
this.myDatasubscription = this._DB.list('mailboxes/' + this.uid).snapshotChanges().pipe(map(actions => {
return actions.map(action => ({ key: action.key, val: action.payload.val() }));
}))
.subscribe(items => {
this.items = [];
this.items = items.map(item => item);
console.log("db results",this.items);
var icount=0;
for (let i in this.items) {
console.log("key",this.items[i].key);
console.log("val",this.items[i].val); 
console.log("----------------------------------);
//checking if something exists
if (this.items[i].key == 'SomeNodePath') {
var log = this.items[i].val;
}
}

} catch (e) {
console.error(e);
}

});
}
}
npm install --save angularfire2 firebase
npm install -D rxjs@6.2.2 rxjs-compat@6.2.2