Angular 2 Pass Async Data
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本文的主要内容是介绍父子组件通信时，如何传递异步的数据。我们将通过一个具体的示例，来介绍不同的处理方式。假设我们有一个博客组件，用来显示博主信息和分类的帖子列表信息。具体如下图所示：
了解完具体需求后，接下来我们来一步步实现该组件。 Post Interfaces and DataPost Interfacespost.interface.ts // each post will have a title and category
export interface Post {
title: string;
category: string;
}
// grouped posts by category
export interface GroupPosts {
category: string;
posts: Post[];
}
Mock Posts Data[
{ "title": "Functional Programming","category": "RxJS" },{ "title": "Angular 2 Component Inheritance","category": "NG2" },{ "title": "RxJS Operators",{ "title": "Angular 2 Http Module - HTTP","category": "WEB" },{ "title": "RxJS Observable",{ "title": "Angular 2 AsyncPipe","category": "NG2" }
]
Blogger Componentposts.component.ts import { Component,Input,OnChanges,OnInit,SimpleChanges } from '@angular/core';
import { BehaviorSubject } from 'rxjs/BehaviorSubject';
import { Post,GroupPosts } from './post.interface';
@Component({
selector: 'exe-posts',template: `
<div class="list-group">
<div *ngFor="let group of groupPosts;" class="list-group-item">
<h4>{{ group.category }}</h4>
<ul>
<li *ngFor="let post of group.posts">
{{ post.title }}
</li>
</ul>
<div>
</div>
`
})
export class PostsComponent implements OnInit,OnChanges {
@Input()
data: Post[];
groupPosts: GroupPosts[];
ngOnInit() {}
ngOnChanges(changes: SimpleChanges) {
console.dir(changes);
}
groupByCategory(data: Post[]): GroupPosts[] {
if (!data) return;
// 获取目录名，使用ES6中Set进行去重处理
const categories = new Set(data.map(x => x.category));
// 重新生成二维数组，用于页面显示
const result = Array.from(categories).map(x => ({
category: x,posts: data.filter(post => post.category === x)
}));
return result;
}
}
blogger.component.ts import { Component,Input } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { Observer } from 'rxjs/Observer';
import { Post } from './post.interface';
@Component({
selector: 'exe-bloggers',template: `
<h1>Posts by: {{ blogger }}</h1>
<div>
<exe-posts [data]="posts"></exe-posts>
</div>
`
})
export class BloggerComponent implements OnInit {
blogger = 'Semlinker';
posts: Post[];
ngOnInit() {
this.getPostsByBlogger()
.subscribe(posts => this.posts = posts);
}
getPostsByBlogger(): Observable<Post[]> {
return Observable.create((observer: Observer<Post[]>) => {
setTimeout(() => {
const posts = [
{ "title": "Functional Programming","category": "NG2" }
];
observer.next(posts);
},2000);
})
}
}
app.component.ts import { Component } from '@angular/core';
@Component({
selector: 'exe-app',template: `
<exe-bloggers></exe-bloggers>
`
})
export class AppComponent {}
以上代码运行完后，你会发现浏览器中只显示 Solutions (方案)Solution 1: Use *ngIf使用 blogger.component.ts template: `
<h1>Posts by: {{ blogger }}</h1>
<div *ngIf="posts">
<exe-posts [data]="posts"></exe-posts>
</div>
`
posts.component.ts ngOnInit() {
this.groupPosts = this.groupByCategory(this.data);
}
Solution 2: Use ngOnChanges当数据绑定输入属性的值发生变化的时候，Angular 将会主动调用 ngOnChanges() 方法。它会获得一个 SimpleChanges 对象，包含绑定属性的新值和旧值，因此我们可以利用 1.移除 blogger.component.ts 组件模板中的 template: `
<h1>Posts by: {{ blogger }}</h1>
<div>
<exe-posts [data]="posts"></exe-posts>
</div>
`
2.更新 posts.component.ts ngOnInit() {
// this.groupPosts = this.groupByCategory(this.data);
}
ngOnChanges(changes: SimpleChanges) {
if (changes['data']) {
this.groupPosts = this.groupByCategory(this.data);
}
}
Solution 3: Use RxJS BehaviorSubject我们也可以利用 RxJS 中 posts.component.ts import { Component,SimpleChanges } from '@angular/core';
import { BehaviorSubject } from 'rxjs/BehaviorSubject';
import 'rxjs/add/operator/takeWhile';
import { Post,OnChanges {
private _data$ = new BehaviorSubject<Post[]>([]);
@Input()
set data(value: Post[]) {
this._data$.next(value);
}
get data(): Post[] {
return this._data$.getValue();
}
groupPosts: GroupPosts[];
ngOnInit() {
this._data$
// 当this.groupPosts有值的时候，会自动取消订阅
.takeWhile(() => !this.groupPosts)
.subscribe(x => {
this.groupPosts = this.groupByCategory(this.data);
});
}
ngOnChanges(changes: SimpleChanges) { }
groupByCategory(data: Post[]): GroupPosts[] {
if (!data) return;
// 获取目录名，使用ES6中Set进行去重处理
const categories = new Set(data.map(x => x.category));
// 重新生成二维数组，用于页面显示
const result = Array.from(categories).map(x => ({
category: x,posts: data.filter(post => post.category === x)
}));
return result;
}
}
上面示例中，我们使用了 RxJS 中 BehaviorSubject，如果想进一步了解详细信息，请参考 - RxJS Subject。 需要注意的是，如果使用 Solution 4: Use Observable除了上面提到的三种方案外，我们还可以使用 Observable 对象。即设置输入属性的类型是 Observable。具体示例如下： posts.component.ts import { Component,OnDestroy,SimpleChanges } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { Subscription } from 'rxjs/Subscription';
import { Post,OnDestroy {
@Input() data: Observable<Post[]>; // 输入属性的类型是Observable
groupPosts: GroupPosts[];
dataSubscription: Subscription; // 用于组件销毁时取消订阅
ngOnInit() {
this.dataSubscription = this.data.subscribe(posts => {
this.groupPosts = this.groupByCategory(posts);
});
}
ngOnChanges(changes: SimpleChanges) { }
ngOnDestroy() {
this.dataSubscription.unsubscribe();
}
groupByCategory(data: Post[]): GroupPosts[] {
if (!data) return;
// 获取目录名，使用ES6中Set进行去重处理
const categories = new Set(data.map(x => x.category));
// 重新生成二维数组，用于页面显示
const result = Array.from(categories).map(x => ({
category: x,posts: data.filter(post => post.category === x)
}));
return result;
}
}
blogger.component.ts import { Component,template: `
<h1>Posts by: {{ blogger }}</h1>
<div>
<exe-posts [data]="posts"></exe-posts>
</div>
`
})
export class BloggerComponent implements OnInit {
blogger = 'Semlinker';
posts: Observable<Post[]>;
ngOnInit() {
this.posts = this.getPostsByBlogger();
}
getPostsByBlogger(): Observable<Post[]> {
return Observable.create((observer: Observer<Post[]>) => {
setTimeout(() => {
const posts = [
{ "title": "Functional Programming",2000);
})
}
}
上面的示例是没有在模板中直接使用 Observable 类型的输入属性，若需要在模板中直接使用的话，可以使用 Angular 2 中的 我有话说1.上面介绍的方案，应该使用哪一种？ 这个还是取决于实际的应用场景，如果数据源只会发生一次变化，那么可以考虑使用 2.组件通信还有哪些方式？ 组件通信的常用方式：@Input、@Output、@ViewChild、模板变量、MessageService、Broadcaster (Angular 1.x $rootScope 中 $on、$broadcast ) 等。 详细的信息，请参考 - Angular 2 Components Communicate 参考资源
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