我在这里有组件代码,当我订阅observable时,服务被调用两次,但是如果我订阅了Behaviorsubject,它只被触发一次,
我可以在我的日志中看到结果,请参阅下面的代码我的组件 方法subscribeToMap()方法在ngOninit上调用。
import { Component, OnInit } from '@angular/core';
import { Router } from '@angular/router';
import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';
// Observable class extensions
import 'rxjs/add/observable/of';
// Observable operators
import 'rxjs/add/operator/catch';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';
import { HeroSearchService } from './hero-search-service';
import { Hero } from './../hero';
@Component({
selector: 'hero-search',
templateUrl: './hero-search.component.html',
styleUrls: [ './hero-search.component.css' ],
providers: [HeroSearchService]
})
export class HeroSearchComponent implements OnInit {
heroes: Observable<Hero[]>;
private searchTerms = new Subject<string>();
constructor(
private heroSearchService: HeroSearchService,
private router: Router) {}
// Push a search term into the observable stream.
search(term: string): void {
this.searchTerms.next(term);
console.log("new " + term);
}
ngOnInit(): void {
this.heroes = this.searchTerms
.debounceTime(300) // wait 300ms after each keystroke before considering the term
.distinctUntilChanged() // ignore if next search term is same as previous
.switchMap(term => {
return term // switch to new observable each time the term changes
// return the http search observable
? this.heroSearchService.search(term)
// or the observable of empty heroes if there was no search term
: Observable.of<Hero[]>([])})
.catch(error => {
// TODO: add real error handling
console.log(error);
return Observable.of<Hero[]>([]);
});
this.subscribeToMap();
}
subscribeToMap(): void{
this.heroes.subscribe(() => console.log("called twice"));
this.searchTerms.subscribe(() => console.log("called once"));
}
gotoDetail(hero: Hero): void {
let link = ['/detail', hero.id];
this.router.navigate(link);
}
}
以下是我服务的代码
import { Injectable } from '@angular/core';
import { Http } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import { Hero } from './../hero';
@Injectable()
export class HeroSearchService {
constructor(private http: Http) {}
search(term: string): Observable<Hero[]> {
console.log("service is called");
return this.http
.get(`api/heroes/?name=${term}`)
.map(response => response.json().data as Hero[]);
}
}
非常感谢!!!
答案 0 :(得分:2)
正确实施订阅时,它与&#34;取消订阅&#34;无关。方法,Observable等。这种行为是由Angular本身设计的。
https://www.reddit.com/r/Angular2/comments/59532r/function_being_called_multiple_times/d95vjlz/
如果您在开发模式下运行,它将运行该功能 至少两次。因为在开发模式下它会进行检查,更改, 然后重新检查以验证,生产模式仅执行第一个 检查,假设您已经完成了质量保证并解决了问题 在检查后改变了价值。
P.S。这可能是您在Dev Mode中面临的下一个问题:)
Angular2 change detection "Expression has changed after it was checked"
答案 1 :(得分:0)
尝试替换此行:
this.heroes = this.searchTerms
有了这个:
this.heroes = this.searchTerms.asObservable()
确保英雄是可观察的,并且您的代码无法在其上意外调用next()
。
您的代码将英雄投射到主题,因此您仍然可以对其执行next()。