我有以下的 Typescript 服务(app.component.ts):
import { Component, OnInit } from '@angular/core';
import { ApiService } from './shared/api.service';
import {PowerPlant} from './shared/models/powerplant.model';
import 'rxjs/add/operator/toPromise';
@Component({
selector: 'app-root',
providers: [ApiService],
templateUrl: './app.component.html',
styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
// represents the URL's
allPowerPlantsURL = 'powerPlants';
// represents the data
powerPlants: PowerPlant[];
ngOnInit(): void {
this.allPowerPlants();
}
constructor(private apiService: ApiService) {
}
allPowerPlants(onlyActive: boolean = false, page: number = 1): void {
const params: string = [
`onlyActive=${onlyActive}`,
`page=${page}`
].join('&');
const path = `${this.allPowerPlantsURL}?${params}`;
this.apiService.get(path)
.toPromise()
.then(elem => {
console.log('In the allPowerPlants');
console.log(elem); **// prints undefined here**
this.powerPlants = <PowerPlant[]> elem; }
)
.catch(this.handleError);
}
private handleError(error: any): Promise<any> {
console.error('An error occurred', error);
return Promise.reject(error.message || error);
}
}
这是我的 app.component.html(只是它的一个片段):
<div class="ui grid posts">
<app-powerplant
*ngFor="let powerPlant of powerPlants"
[powerPlant]="powerPlant">
</app-powerplant>
</div>
现在,在我的 powerplant.component.html 中,我有这个:
从'@angular/core'导入{Component,Input,OnInit};进口{。 5}来自'../shared/models/powerplant.model';
@Component({
selector: 'app-powerplant',
templateUrl: './powerplant.component.html',
styleUrls: ['./powerplant.component.css']
})
export class PowerplantComponent implements OnInit {
@Input() powerPlant: PowerPlant;
constructor() { }
ngOnInit() {
}
}
最后,应该显示 PowerPlant 项目的那个是这样的:
<div class="four wide column center aligned votes">
<div class="ui statistic">
<div class="value">
{{ powerPlant.powerPlantId }}
</div>
<div class="label">
Points
</div>
</div>
</div>
<div class="twelve wide column">
<div class="value">
MaxPower: {{ powerPlant.maxPower }} MinPower: {{ powerPlant.minPower }}
</div>
<div class="value">
MaxPower: {{ powerPlant.maxPower }} MinPower: {{ powerPlant.minPower }}
</div>
<div class="value">
PowerPlantType: {{ powerPlant.powerPlantType }} Organization: {{ powerPlant.powerPlantName }}
</div>
</div>
我可以看到服务器正在向我发送数组,因为 get 方法显示以下控制台日志:
get(path: string, params: URLSearchParams = new URLSearchParams()): Observable<any> {
console.log('sending request to ' + `${environment.api_url}${path}`);
return this.http.get(`${environment.api_url}${path}`, { search: params })
.catch(this.formatErrors)
.map((res: Response) => {
console.log(res.json());
res.json();
});
}
在 console.log 行打印我的内容如截图所示:
那么为什么 toPromise()失败了?仅供参考,这就是我的 PowerPlant 模型的样子:
export interface PowerPlant {
powerPlantId: number;
powerPlantName: string;
minPower: number;
maxPower: number;
powerPlantType: string;
rampRateInSeconds?: number;
rampPowerRate?: number;
}
2 回答
是否有使用
toPromise()
方法的特定原因?正常订阅时是否有效?尝试改变这个
对此:
那么可能是因为您没有在
.map()
方法中返回解析后的结果,因此您无法在您的承诺/订阅中获得响应。它与您的 ApiService 有关,您忘记在
.map
中返回res.json