Angular5 服务调用不适用于 ngOnInit

Question

当我导航到结果组件时，ngOnInit 中的服务按预期工作。然后我打开侧面菜单，导航到另一个页面，然后再次导航到结果页面。但是这次页面不呈现结果。而是呈现 ng-template。控制台上没有错误，什么都没有。 ngOnInit 正在工作，正在显示 console.log('init');但服务电话没有。如果我将服务调用粘贴到构造函数或函数中，它也不起作用。我试过有和没有 ngZone，什么都没有..

我需要指出的是，如果我在“结果”页面上直接按 F5，它就会起作用。就在我通过 this.router.navigate(['/resultados']); 导航到它时那是行不通的。

这是结果组件:

import { Component, OnInit, NgZone } from '@angular/core';
import { Router, ActivatedRoute, ParamMap } from '@angular/router';
import { NavService } from '../shared/nav.service';
import {AngularFirestore} from 'angularfire2/firestore';
import {firestoreService} from '../shared/firestore.service';
import {Usuario} from '../../models/usuario'

@Component({
    selector: 'resultados',
    templateUrl: 'resultados.component.html'
})

export class ResultadosComponent implements OnInit {
    servId:any;
    users: Usuario[];
    constructor(
        private fService: firestoreService,
        private service:NavService,
        private router: Router,
        private zone: NgZone
      ) { }

    ngOnInit() { 
        console.log('init')
        this.fService.getUsers().subscribe(users=>{
            this.zone.run(()=>{
                this.users = users;
            })

        })
    }
}

这是结果 HTML:

<div class="resultados" *ngIf="users?.length > 0;else noUsers"> 
<ul *ngFor="let user of users">
    <li>{{user.uid}}</li>
</ul>
</div>
<ng-template #noUsers>
<hr>
<h5>Nenhum usuário cadastrado</h5>
</ng-template>

这是 firestore.service:

    import { Injectable } from '@angular/core';
    import {AngularFirestore, AngularFirestoreCollection, 
    AngularFirestoreDocument} from 'angularfire2/firestore';
    import {Usuario} from '../../models/usuario'
    import {Observable} from 'rxjs/Observable';


@Injectable()
export class firestoreService {
    usersCollection: AngularFirestoreCollection<Usuario>;
    users:Observable<Usuario[]>;

     constructor(public afs:AngularFirestore){

         this.users = this.afs.collection('users').valueChanges();

     }

    getUsers(){
        return this.users;
    }

}

Answer 1

在 OnDestroy 中使用取消订阅有效!谢谢@tam5。

import { Component, OnInit, NgZone } from '@angular/core';
import { Router, ActivatedRoute, ParamMap } from '@angular/router';
import { NavService } from '../shared/nav.service';
import {AngularFirestore} from 'angularfire2/firestore';
import {firestoreService} from '../shared/firestore.service';
import {Usuario} from '../../models/usuario'
import { OnDestroy } from '@angular/core/src/metadata/lifecycle_hooks';
import { Subscription } from 'rxjs/Subscription'; //<== added this

@Component({
    selector: 'resultados',
    templateUrl: 'resultados.component.html'
})

export class ResultadosComponent implements OnInit , OnDestroy {
    servId:any;
    users: Usuario[];
    private subscription: Subscription = new Subscription(); //<== added this

    constructor(
        private fService: firestoreService,
        private service:NavService,
        private router: Router,
        private zone: NgZone
      ) {


      }

    ngOnInit() { 
        console.log('init')
    this.subscription.add(this.fService.getUsers().subscribe(users=>{ //<== added this

            this.zone.run(()=>{
                this.users = users;
            })

        }))
    }

    ngOnDestroy(){ //<== added this
        this.subscription.unsubscribe();
    }
}