在组件呈现之前,我想从我的API中加载一个事件。目前我正在使用我的API服务,并从组件的ngOnInit函数中调用它。
我的EventRegister
组件:
import {Component, OnInit, ElementRef} from "angular2/core";
import {ApiService} from "../../services/api.service";
import {EventModel} from '../../models/EventModel';
import {Router, ROUTER_DIRECTIVES, ROUTER_PROVIDERS, RouteConfig, RouteParams, RouterLink} from 'angular2/router';
import {FORM_PROVIDERS, FORM_DIRECTIVES, Control} from 'angular2/common';
@Component({
selector: "register",
templateUrl: "/events/register"
// provider array is added in parent component
})
export class EventRegister implements OnInit {
eventId: string;
ev: EventModel;
constructor(private _apiService: ApiService,
params: RouteParams) {
this.eventId = params.get('id');
}
fetchEvent(): void {
this._apiService.get.event(this.eventId).then(event => {
this.ev = event;
console.log(event); // Has a value
console.log(this.ev); // Has a value
});
}
ngOnInit() {
this.fetchEvent();
console.log(this.ev); // Has NO value
}
}
我的EventRegister
模板
<register>
Hi this sentence is always visible, even if `ev property` is not loaded yet
<div *ngIf="ev">
I should be visible as soon the `ev property` is loaded. Currently I am never shown.
<span>{{event.id }}</span>
</div>
</register>
我的API服务
import "rxjs/Rx"
import {Http} from "angular2/http";
import {Injectable} from "angular2/core";
import {EventModel} from '../models/EventModel';
@Injectable()
export class ApiService {
constructor(private http: Http) { }
get = {
event: (eventId: string): Promise<EventModel> => {
return this.http.get("api/events/" + eventId).map(response => {
return response.json(); // Has a value
}).toPromise();
}
}
}
在ngOnInit
函数中的API调用完成之前,该组件会被渲染。因此,我从未在视图模板中看到事件ID。所以这看起来是一个异步问题。我期望ev
(EventRegister
组件)的绑定在ev
属性被设置后能做一些工作。不幸的是,当属性被设置时,它并没有显示标记为*ngIf="ev"
的
问题:我的方法可行吗?如果不是,加载数据的最佳方式是什么?
注意:在此Angular2教程中使用了ngOnInit
方法。
编辑:
两个可能的解决方案。首先是放弃fetchEvent
,直接在ngOnInit
函数中使用API服务。
ngOnInit() {
this._apiService.get.event(this.eventId).then(event => this.ev = event);
}
第二种解决方案。与给出的答案相似。
fetchEvent(): Promise<EventModel> {
return this._apiService.get.event(this.eventId);
}
ngOnInit() {
this.fetchEvent().then(event => this.ev = event);
}