typescript – Angular2：在渲染组件之前如何加载数据？

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，该组件被渲染。所以我从来没有看到我的视图模板中的事件ID。所以看起来这是一个ASYNC问题。我希望ev(EventRegister组件)在设置ev属性后进行一些工作。遗憾的是，当属性设置时，它不会显示标有* ngIf =“ev”的div。

问题：我使用好的方法吗？如果不;在组件开始呈现之前加载数据的最佳方式是什么？

注意：在此angular2 tutorial中使用ngOnInit方法。

编辑：

两种可能的解决方案。首先是撷取fetchEvent，并在ngOnInit函数中使用API??服务。

ngOnInit() {
    this._apiService.get.event(this.eventId).then(event => this.ev = event);
}

第二个解决方案就像给出的答案。

fetchEvent(): Promise<EventModel> {
    return this._apiService.get.event(this.eventId);
}

ngOnInit() {
    this.fetchEvent().then(event => this.ev = event);
}