Angularv4.初体验


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15 Http请求 Http Requests

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15 -- Http Requests 在前面VideoList的内容列表我们是预定义在代码里的,这节我们将通过的Http的方式从外部获取。

创建文件assets/json/videos.json 并将下面这个定义的数组

  videoList = [
    {
      name: 'Item 1',
      slug: 'item-1',
      // embed: `XMzU5MjI4NTI3Mg`,
      embed: `95851db6%2Dd22f%2D4e32%2D8d7c%2Dc06a907f9457`,      
    },
    {
      name: 'Item 2',
      slug: 'item-2',
      // embed: `XMzU5MjI4NTI3Mg`,
      embed: `10d528b2%2Ddc88%2D4ad5%2D8bb5%2D7aceff22c5ef`,
    },
    {
      name: 'Item 3',
      slug: 'item-3',
      embed: null,
    }
  ]

在json文件里定义如下

  [
    {
      "name": "Item 1",
      "slug": "item-1",
      "embed": "95851db6%2Dd22f%2D4e32%2D8d7c%2Dc06a907f9457"
    },
    {
      "name": "Item 2",
      "slug": "item-2",
      "embed": "10d528b2%2Ddc88%2D4ad5%2D8bb5%2D7aceff22c5ef"
    },
    {
      "name": "Item 3",
      "slug": "item-3",
      "embed": null,
    }
  ]

注意:每个字典最后一个元素转换不能有逗号,否则报错

接下来我们需要在页面加载时通过Http Request获取这些数据。

在video-list.component.ts添加支持

import { Http } from '@angular/http';

  private req:any

  constructor(private http:Http) { }

  ngOnInit() {
    this.req = this.http.get("assets/json/videos.json").subscribe(data=>{
      console.log(data.json())
    })
  }

  ngOnDestory(){
    this.req.unsubscribe()
  }

确保app.modules.ts里HttpModule已导入

import { HttpModule } from '@angular/http';

@NgModule({
  imports: [
    //ngx-bootstraps
    BsDropdownModule.forRoot(),
    CarouselModule.forRoot(),
    BrowserModule,
    AppRoutingModule,
    HttpModule,
  ],

上面的代码中我们已经能够从json文件中获取配置内容了,接下来将这些内容应用到模板中

  videoList : [any];

  ngOnInit() {
    this.req = this.http.get("assets/json/videos.json").subscribe(data=>{
      this.videoList = data.json() as [any];
    })
  }

接下来,在video-detail中进行更新

在video-detail.component.ts添加json数据的处理

同样,导入http模块。在OnInit函数是将对应的json数据赋值给video变量

import { Http } from '@angular/http';

  private req:any
  video: any;
  constructor(private route: ActivatedRoute, private http:Http) { }

  ngOnInit() {
    this.routeSub = this.route.params.subscribe(params => {
      this.slug = params['slug']
      this.req = this.http.get("assets/json/videos.json").subscribe(data=>{
        data.json().filter(item=>{
          if(item.slug == this.slug){
            this.video = item
          }
        })
      })      
    }) 
  }  

  ngOnDestroy() {
    this.routeSub.unsubscribe()
    this.req.unsubscribe()
  }  

在html添加模板内容

    <h1>{{video.name}}</h1>
    <p>
        {{video.slug}}
    </p>

如果仅仅是上面内容,会报错,因为刚开始加载时,数据内容还没赋值,这个时候模板的渲染会出错。

可以有几个方法来解决

  1. 添加默认变量
  video = {
    name: 'Item 1',
    slug: 'item-1',
    embed: `95851db6%2Dd22f%2D4e32%2D8d7c%2Dc06a907f9457`,      
  }
  1. 添加判断*ngIF
<div *ngIf="video">
    <h1>{{video.name}}</h1>
    <p>
        {{video.slug}}
    </p>
</div>
  1. 添加判断?
<div *ngIf="!video">Loading</div>
<h1>{{video?.name}}</h1>
<p>
    {{video?.slug}}
</p>