Angular 4 HTTP不返回JSON正文

Question

我的打字稿中有以下方法！

allPowerPlants(onlyActive: boolean = false, page: number = 1): PowerPlant[] {
    const params: string = [
      `onlyActive=${onlyActive}`,
      `page=${page}`
    ].join('&');
    const path = `${this.allPowerPlantsURL}?${params}`;
    this.apiService.get(path).map(
      powerplants => {
        powerplants.map(item => {
          if (this.isPowerPlant(item)) {
            // make the item an instance of PowerPlant
            this.powerPlants.push(item as PowerPlant);
          }
      });
    },
    err => {
        console.log('oops **** some error happened');
      // handle error
    });
    console.log('powerplants obtained is *****************+ ');
    console.log(this.powerPlants);
    return this.powerPlants;
  }

我的get方法如下所示：

import { Injectable } from '@angular/core';
import { environment } from '../../environments/environment';
import { Headers, Http, Response, URLSearchParams } from '@angular/http';
import { Observable } from 'rxjs/Rx';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';

@Injectable()
export class ApiService {
  loading: boolean;
  data: Object;
  constructor(
    private http: Http,
  ) {}


    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('response as json is ' + res.json());
            res.json();
        });
      }
}

我的isPowerPlant方法如下所示：

isPowerPlant(item: any): item is PowerPlant {
    // check for the required properties of PowerPlant here and return true/false.
    // example:
    console.log('in the static method');
    const vvvv = item['maxPower'] && item['minPower'];
    console.log(vvvv);
    return vvvv;
  }

我期待在console.log中看到一些数据（'响应为json是'），但奇怪的是它什么都没打印！ 请求甚至没有到服务器！

但是，当我将我的allPowerPlants方法更改为不映射get方法时，而是订阅如下：

this.apiService.get(path).subscribe(...)

我从服务器日志中看到正在提供请求时，我可以看到从服务器获取的一些数据。

我想做以下事情：

我希望allPowerPlants返回一个PowerPlants数组，定义如下：

export interface PowerPlant {
  powerPlantId: number;
  powerPlantName: string;
  minPower: number;
  maxPower: number;
  powerPlantType: string;
  rampRateInSeconds?: number;
  rampPowerRate?: number;
}

现在因为我的get方法是一个Observable，我看到我的Angular应用程序正在对服务器进行大量的调用，因为从我的服务器日志中可以看到：

[info] application - GET /powerPlants?onlyActive=false&page=1 took 3192ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2974ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2701ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2682ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2885ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2920ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2552ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2564ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2598ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2612ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2615ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2621ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2636ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2609ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2701ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2544ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2588ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2532ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2586ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2570ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2652ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2624ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2661ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2618ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2611ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2624ms HTTP status >> 200
[info] application - GET /powerPlants?onlyActive=false&page=1 took 2620ms HTTP status >> 200

这是我的服务器发送的实际数据：

[ {
  "powerPlantId" : 1,
  "powerPlantName" : "Organization-001",
  "minPower" : 20,
  "maxPower" : 100,
  "powerPlantType" : "OnOffType"
}, {
  "powerPlantId" : 2,
  "powerPlantName" : "Organization-001",
  "minPower" : 100,
  "maxPower" : 800,
  "rampPowerRate" : 100,
  "rampRateInSeconds" : 100,
  "powerPlantType" : "RampUpType"
}, {
  "powerPlantId" : 3,
  "powerPlantName" : "Organization-002",
  "minPower" : 200,
  "maxPower" : 400,
  "rampPowerRate" : 50,
  "rampRateInSeconds" : 50,
  "powerPlantType" : "RampUpType"
}, {
  "powerPlantId" : 4,
  "powerPlantName" : "Organization-002",
  "minPower" : 400,
  "maxPower" : 800,
  "powerPlantType" : "OnOffType"
} ]

如何使我的allPowerPlants只调用我的服务器一次，但同时处理get方法的Observable结果？

这就是我如何利用HTML中的数据：

<div class="ui grid posts">
  <app-powerplant
    *ngFor="let powerPlant of allPowerPlants()"
    [powerPlant]="powerPlant">
  </app-powerplant>
</div>

Answer 1

以下是从服务器调用数据的代码片段

this.apiService.get(path).map(
      powerplants => {
       ...
          }

停在那儿。 没有数据的原因是你没有订阅它！ 你应该做这个

this.apiService.get(path).subscribe(
      powerplants => {
        this.powerPlants = powerplants
        //remove the mapping. you can do it in your service.
    },
    err => {
        console.log('oops **** some error happened');
      // handle error
    });

并在您的服务

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) => {
            <PowerPlant[]> res.json();
        });
      }

请注意，我的映射可能是错误的，因为您没有显示返回数据的实际值。

希望这可以帮助。

Answer 2

好的，网上有很多关于如何处理http请求的例子，在这里吨...

通常你有一个get方法的服务， 不要使用像GET这样的保留字来调用你的方法 ...在你的情况下将是getAllPowerplants

在您的情况下，API服务看起来很好（方法名称除外）

然后在组件上，你会有这样的东西

this.apiService.getAllPowerplants.subscribe(data => {
  console.log(data);
});

并且显然只订阅它一次（ngOnInit是个好地方）