2个角度分量之间的变化检测

Question

我有2个组成部分-导航（显示主题列表）和视频列表（显示所选列表）。

我要做的就是当我单击某个导航元素时，视频列表标题将更改。

navigation.component.ts

import { Component, OnInit } from '@angular/core';
import {DataService} from "../../../services/data.service";

@Component({
  selector: 'app-navigation',
  templateUrl: './navigation.component.html',
  styleUrls: ['./navigation.component.css'],
  providers: [DataService]
})
export class NavigationComponent implements OnInit {
  allTopics: any;
  mainTopics: any;
  constructor(private data: DataService) {
    this.allTopics      = this.data.getAllTopics().subscribe(data => {
      this.allTopics    = data;
      this.mainTopics   = Object.keys(data);
    } );
  }

  setCurrentSelectedSubTopic(subTopic) {
    this.data.setCurrentSelectedSubTopic(subTopic)
  }

  ngOnInit() {
  }
}

在这个组件上，我有一个点击动作：

(click)="setCurrentSelectedSubTopic(subTopic)"

当我单击时，我会得到一个很好的console.log。 此功能更新服务。

data.service.ts

import { Injectable }     from '@angular/core';
import { Observable }     from 'rxjs/Observable';
import { Http, Response } from '@angular/http';

@Injectable()
export class DataService {
  currentSelectedSubTopic: any;
  constructor(private http: Http) {}

  getAllTopics(): Observable<any> {
    return this.http.get(`http://localhost:4200/getAllTopics`)
      .map(res => res.json())
  }

  setCurrentSelectedSubTopic(subTopic) {
    this.currentSelectedSubTopic = subTopic;
  }
}

该服务被注入到video-list.component.ts

import { Component, OnInit } from '@angular/core';
import { DataService } from '../../../services/data.service';

@Component({
  selector: 'app-video-list',
  templateUrl: './video-list.component.html',
  styleUrls: ['./video-list.component.css'],
  providers: [DataService]
})
export class VideoListComponent implements OnInit {
  constructor(public data: DataService) {

  }

  ngOnInit() {
  }
}

它的html是：

<p>
{{data.currentSelectedSubTopic ? data.currentSelectedSubTopic.Name : ''}}
</p>

无论我尝试做什么，此html都不会改变

Answer 1

您看不到立即更新，因为您正在使用DataService不同实例。 要使其正常工作，请确保具有一个服务实例。 为此，将providers数组放置在AppModule's或RootComponent's @NgModule装饰器中，如下所示，

@NgModule({
   ...
   ...
   providers: [DataService]
   ...
})

并从两个单独的组件中删除providers: [DataService] 。