我在学习Angular 4并遇到了一个我似乎无法找到解决方案的问题。这里是背景: 我有一个简单的应用程序,显示有关美国总统的信息。 后端是由webapi提供的其余API ...这工作正常。 前端是一个Angular应用程序。Angular 2 - http.get永远不会打电话
我将问题简化为3个组件,1个数据服务和1个模型。 这里是模型:
export class President {
constructor(
public id: number,
public presidentName: string,
public presidentNumber: number,
public yearsServed: string,
public partyAffiliation: string,
public spouse: string) {}
}
的3个组分是 1.的SearchComponent 2. HomeComponent 3. PresidentComponent
当应用程序自举时,它加载ApplicationComponent - 它是根组件:
import { Component, ViewEncapsulation } from '@angular/core';
@Component({
selector: 'my-app',
template: `
<search-component></search-component>
<home-component></home-component>
`
})
export class ApplicationComponent {}
PresidentComponent是HomeComponent的子组件。加载home组件时,它会对api进行http调用以获取总统列表,并为返回的每一行呈现1个presidentComponent。这工作正常。
什么即时试图做的是实现搜索功能,其中DataService在暴露的EventEmitter并提供搜索方法如下所示:
import { Injectable, EventEmitter, Output } from '@angular/core'
import { President } from '../models/President'
import { Http } from '@angular/http';
import 'rxjs/add/operator/toPromise';
import 'rxjs/add/operator/map';
import { Observable } from 'rxjs/Observable';
@Injectable()
export class DataService {
constructor(private http: Http) {
}
searchEvent: EventEmitter<any> = new EventEmitter();
// simple property for the url to the api
get presidentUrl {
return "http://localhost:51330/api/presidents";
}
search(params: any): Observable<President[]> {
let encParams = encodeParams(params);
console.log(encParams);
return this.http
.get(this.presidentUrl, {search: encParams})
.map(response => response.json());
}
getParties(): String[] {
return ['Republican', 'Democrat', 'Federalist', 'Whig', 'Democratic-Republican', 'None'];
}
getPresidents(): Observable<President[]> {
return this.http.get(this.presidentUrl)
.map(response => response.json());
}
}
/**
* Encodes the object into a valid query string.
* this function is from the book Angular2 Development with TypeScript
*/
function encodeParams(params: any): URLSearchParams {
return Object.keys(params)
.filter(key => params[key])
.reduce((accum: URLSearchParams, key: string) => {
accum.append(key, params[key]);
return accum;
}, new URLSearchParams());
}
搜索组件的房屋搜索表单,并点击搜索按钮时,它执行onSearch()函数,并调用数据服务发出:
onSearch(){
if(this.formModel.valid){
console.log('emitting event from search.ts');
this.dataService.searchEvent.emit(this.formModel.value);
}
}
然后,在HomeComponent,我想订阅此事件,并通过DataService在执行搜索时,它触发:
ngOnInit(): void {
//when component loads, get list of presidents
this.dataService.getPresidents()
.subscribe(
presidents => {
console.log('sub');
this.presidents = presidents;
},
error => console.error(error)
)
//when search event is fired, do a search
this.dataService.searchEvent
.subscribe(
params => {
console.log('in home.ts subscribe ' + JSON.stringify(params));
this.result = this.dataService.search(params);
},
err => console.log("cant get presidents. error code: %s, URL: %s"),
() => console.log('done')
);
}
当我在浏览器中运行它时,除了http调用以外的所有工作都不会执行。如果我在数据服务本身中订阅()到http.get调用,它会执行,但为什么我必须在HomeComponent上设置订阅时这样做? 我想处理HomeComponent中的Observable,并根据搜索结果更新UI中显示的总统列表。 任何意见,不胜感激。
@chsdk http://www.typescriptlang.org/docs/handbook/classes.html#accessors – jonrsharpe