FirebaseList - Unable to access parse data fetched from firebase

问题

I'm getting " Error: InvalidPipeArgument: '[object Object]' for pipe 'AsyncPipe' " when running the following code.

html template:

 <ion-list>
    <ion-item-sliding *ngFor="let item of shoppingItems | async">
      <ion-item>
        {{ item.$value }}
      </ion-item>
      <ion-item-options side="right">
        <button ion-button color="danger" icon-only (click)="removeItem(item.$key)"><ion-icon name="trash"></ion-icon></button>
      </ion-item-options>
    </ion-item-sliding>
  </ion-list>

page ts:

shoppingItems: AngularFireList<any>;
constructor(public navCtrl: NavController, public firebaseProvider: FirebaseProvider) {
    this.shoppingItems = this.firebaseProvider.getShoppingItems();
}

firebase provider

  constructor(public afd: AngularFireDatabase) {
    console.log('Hello FirebaseProvider Provider');
    console.log("Shopping items"+afd.list('/shoppingItems/'))
  }

  getShoppingItems() {

    console.log("Shopping items"+this.afd.list('/shoppingItems/'))
    return this.afd.list('/shoppingItems/');
  }
  addItem(name) {
    this.afd.list('/shoppingItems/').push(name);
  }

firebase db

shoppingItems
 -KxmiUt64GJsPT84LQsI: "qwerty"
 -KxmifqyfD41tRPwFh07: "key"

From the web app I was able to add items to firebase db. But I wasn't able to render the data from firebase. I am getting the above mentioned error.

Thanks in advance for your help.

回答1:

AngularFire2 V5

this.afd.list('/shoppingItems/') does not return an asynchronous observable which is supposed to work with async pipe. It returns a reference to the List in the real-time database. You need to use valueChanges() to return that.

In your provider return the observable,

 getShoppingItems() {

    console.log("Shopping items"+this.afd.list('/shoppingItems/'))
    return this.afd.list('/shoppingItems/').valueChanges();//here
  }

If you are accessing through $key/$value, Check the upgrade details for angularfire2 v4 to 5. This is because FirebaseList is deprecated and AngularFireList is now returned from version 5.

Calling .valueChanges() returns an Observable without any metadata. If you are already persisting the key as a property then you are fine. However, if you are relying on $key, then you need to use .snapshotChanges()

You need to use snapshotChanges()

 getShoppingItems() {

    console.log("Shopping items"+this.afd.list('/shoppingItems/'))
    return this.afd.list('/shoppingItems/').snapshotChanges();//here
  }

To access $key or $value in html, use item.payload.key and item.payload.val()

回答2:

Add ionViewDidLoad life cycle in the home.ts file and instead of constructor load your item in ionViewDidLoad , replace your constructor with below code

    constructor(public navCtrl: NavController, public firebaseProvider: FirebaseProvider) {

  }

  ionViewDidLoad() {
    this.shoppingItems = this.firebaseProvider.getShoppingItems();
    console.log(this.shoppingItems);
  }

回答3:

Import at page.ts

 import { Component } from '@angular/core';
 import { IonicPage, NavController, NavParams } from 'ionic-angular';
 import { AngularFireDatabase} from 'angularfire2/database';
 import { Observable } from "rxjs/Observable";
 import { ShoppingItem } from '../../model/shoppingitem';

import your provider the right way from your provider

 import { FirebaseProvider } from '../../providers/firebase/firebase';

 export class Page {

  shoppingItems:Observable<ShoppingItem[]>;

 constructor(public navCtrl: NavController, 
             public firebaseProvider: FirebaseProvider) {

                this.shoppingItems=this.firebaseProvider
                .getShoppingItem()
                .snapshotChanges()
                .map(
                  changes=>{
                    return changes.map(c=>({
                      key:c.payload.key, ...c.payload.val(),
                    }));
                  }
                );
          }
        }

     }

firebaseProvider

note the 'shopping-list' is the table at the firebase database

  private itemListRef = this.afDatabase.list<ShoppingItem>('shopping-list');

  constructor(private afDatabase: AngularFireDatabase) {}

 .getShoppingItem(){

   return this.itemListRef;

  }
 }

Your shoppingitem model

 export interface ShoppingItem{
  key?:string;
  }

来源：https://stackoverflow.com/questions/47048556/firebaselist-unable-to-access-parse-data-fetched-from-firebase