在Angular 2 v2.0.1中,onInit被調用兩次。 (很明顯,我也做一些錯誤的,當它被稱爲一次,但現在這不是問題)Angular 2 http可以被觀察到被調用兩次
這裏是我的Plunker:http://plnkr.co/edit/SqAiY3j7ZDlFc8q3I212?p=preview
這裏的服務代碼:
import {Injectable} from '@angular/core';
import {Http, Response} from '@angular/http';
import {Observable} from 'rxjs/Rx';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/do';
@Injectable()
export class DemoService {
constructor(private http:Http) { }
// Uses http.get() to load a single JSON file
getData() {
return this.http.get('./src/data.json')
.map((res:Response) => res.json())
.do(data => console.log(data))
.subscribe(data => {
return <PageContent[]>data;
}, error => console.log("there was an error!"));
}
}
export class PageContent {
constructor(public _id: string,
public tag: string,
public title: string,
public body?:string,
public image?: string) {}
}
...以及使用它的簡單組件。
//our root app component
import {Component, NgModule, OnInit } from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import { DemoService, PageContent } from './service';
import { HttpModule } from '@angular/http';
@Component({
selector: 'my-app',
template: `
<div>
<h2>Hello {{name}}</h2>
</div>
<div *ngFor="let page of pages">
{{ page.title }}
</div>
`
})
export class App implements OnInit {
name:string;
pages: PageContent[] = [];
constructor(private _service: DemoService) {
this.name = 'Angular2'
this.loadData(); // <-- this is called once
}
ngOnInit() {
//this.loadData(); // <-- this is called twice
}
loadData(){
this.pages = this._service.getData();
console.log(this.pages);
}
}
@NgModule({
imports: [ BrowserModule, HttpModule ],
declarations: [ App ],
providers: [DemoService],
bootstrap: [ App ]
})
export class AppModule {}
免責聲明:它的示數出來,但你可以看到它被服務一次當正在從構造稱爲服務方法,但它被調用兩次當它是ngOnInit鉤內。
我的問題是,爲什麼它被從OnInit函數調用兩次?
UPDATE:解決所有的答案:
這是新的服務方法:
getData() {
return this.http.get('./src/data.json')
.map((res:Response) => res.json() as PageContent[]);
}
...這是新組件的方法:
loadData(){
this._service.getData()
.subscribe(data => this.pages = data);
}
刪除模板的一部分使用ngFor並導致應用程序失敗,並且您會在正常情況下看到它只被調用一次。 –
@JBNizet - 但我需要* ngFor來顯示數據。 –