Angular HTTP GET带有TypeScript错误HTTP . GET(…)。Map不是[null]中的函数

我在Angular中的HTTP有一个问题。

我只是想获得一个JSON列表，并在视图中显示它。

服务类

import {Injectable} from "angular2/core";
import {Hall} from "./hall";
import {Http} from "angular2/http";
@Injectable()
export class HallService {
    public http:Http;
    public static PATH:string = 'app/backend/'    

    constructor(http:Http) {
        this.http=http;
    }

    getHalls() {
           return this.http.get(HallService.PATH + 'hall.json').map((res:Response) => res.json());
    }
}

在HallListComponent中，我从服务中调用getHalls方法:

export class HallListComponent implements OnInit {
    public halls:Hall[];
    public _selectedId:number;

    constructor(private _router:Router,
                private _routeParams:RouteParams,
                private _service:HallService) {
        this._selectedId = +_routeParams.get('id');
    }

    ngOnInit() {
        this._service.getHalls().subscribe((halls:Hall[])=>{ 
            this.halls=halls;
        });
    }
}

然而，我有一个例外:

TypeError: this.http.get(……)。Map不是[null]中的函数

hall-center.component

import {Component} from "angular2/core";
import {RouterOutlet} from "angular2/router";
import {HallService} from "./hall.service";
import {RouteConfig} from "angular2/router";
import {HallListComponent} from "./hall-list.component";
import {HallDetailComponent} from "./hall-detail.component";
@Component({
    template:`
        <h2>my app</h2>
        <router-outlet></router-outlet>
    `,
    directives: [RouterOutlet],
    providers: [HallService]
})

@RouteConfig([
    {path: '/',         name: 'HallCenter', component:HallListComponent, useAsDefault:true},
    {path: '/hall-list', name: 'HallList', component:HallListComponent}
])

export class HallCenterComponent{}

app.component

import {Component} from 'angular2/core';
import {ROUTER_DIRECTIVES} from "angular2/router";
import {RouteConfig} from "angular2/router";
import {HallCenterComponent} from "./hall/hall-center.component";
@Component({
    selector: 'my-app',
    template: `
        <h1>Examenopdracht Factory</h1>
        <a [routerLink]="['HallCenter']">Hall overview</a>
        <router-outlet></router-outlet>
    `,
    directives: [ROUTER_DIRECTIVES]
})

@RouteConfig([
    {path: '/hall-center/...', name:'HallCenter',component:HallCenterComponent,useAsDefault:true}
])
export class AppComponent { }

tsconfig.json

{
  "compilerOptions": {
    "target": "ES5",
    "module": "system",
    "moduleResolution": "node",
    "sourceMap": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "removeComments": false,
    "noImplicitAny": false
  },
  "exclude": [
    "node_modules"
  ]
}

当前回答

只是一些背景知识……新发布的服务器通信开发指南(最后)讨论/提到/解释了这一点:

The RxJS library is quite large. Size matters when we build a production application and deploy it to mobile devices. We should include only those features that we actually need. Accordingly, Angular exposes a stripped down version of Observable in the rxjs/Observable module, a version that lacks almost all operators including the ones we'd like to use here such as the map method. It's up to us to add the operators we need. We could add each operator, one-by-one, until we had a custom Observable implementation tuned precisely to our requirements.

所以正如@Thierry已经回答的那样，我们可以只引入我们需要的操作符:

import 'rxjs/add/operator/map';
import 'rxjs/operator/delay';
import 'rxjs/operator/mergeMap';
import 'rxjs/operator/switchMap';

或者，如果我们懒得，我们可以引入完整的操作符集。警告:这将添加所有50+运营商到你的应用程序包，并将影响加载时间

import 'rxjs/Rx';

2016-01-27 17:19:58

其他回答

Angular版本6 "0.6.8" RXJS版本6 "^6.0.0"

此解决方案适用于:

  "@angular-devkit/core": "0.6.8",
  "rxjs": "^6.0.0"

我们都知道angular每天都在开发，所以每天都有很多变化，这个解决方案是针对angular 6和RXJS 6的首先要使用HTTP，你应该导入它从: 毕竟你必须在app.module.ts中声明HttpModule

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

你必须将HttpModule添加到Ngmodule -> imports中

  imports: [
    HttpModule,
    BrowserModule,
    FormsModule,
    RouterModule.forRoot(appRoutes)
  ],

第二，使用map，你应该首先导入管道:

import { pipe } from 'rxjs';

第三，你需要从下面导入map函数:

import { map } from 'rxjs/operators';

你必须像下面这个例子一样在管道中使用map:

 constructor(public http:Http){  }

    getusersGET(){
        return this.http.get('http://jsonplaceholder.typicode.com/users').pipe(
         map(res => res.json()  )  );
    }

那太好了祝你好运!

2018-09-23 12:37:34

这是因为你正在使用RXJS，在RXJS函数不是静态的，这意味着你不能直接调用它们，你必须调用管道内的方法，并从RXJS库导入该函数

但是如果你正在使用rxjs-compat，那么你只需要导入rxjs-compat操作符

2018-07-23 15:27:03

没错，RxJs已经在一个单独的模块中分离了它的map操作符，现在你需要像任何其他操作符一样显式导入它。

进口rxjs /添加/运营商/地图;

你会没事的。

2017-10-28 12:11:01

因为angular2中的Http服务返回一个Observable类型，从你的Angular2安装目录(在我的例子中是'node_modules')，我们需要使用http服务在你的组件中导入Observable的map函数，如下所示: