如何从 HttpClient 获取 json 文件？

Question

我正在尝试从 HttpClient 获取 json 文件，但在添加 .subscribe

时出现错误

进口：

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders, HttpClientModule } from '@angular/common/http';
import { HttpModule, Request, Response, Headers, Http } from '@angular/http';
import { Observable } from 'rxjs';

我的代码：

当我添加 .subscribe（图中黄色标记）时，出现以下错误。这是什么意思？

Object { _body: error, status: 0, ok: false, statusText: "", headers: Object, type: 3, url: null }

Answer 1

如果你想让事情变得非常清晰和有条理，你应该在 angular 中创建一个服务并从你的组件调用该服务。

例如这样：

Service.ts:

import { Injectable } from "@angular/core";
import { Observable, throwError } from "rxjs";
import {
  HttpClient,
  HttpHeaders,
  HttpErrorResponse
} from "@angular/common/http";
import { catchError, map } from "rxjs/operators";

// Set the http options
const httpOptions = {
  headers: new HttpHeaders({ "Content-Type": "application/json", "Authorization": "c31z" })
};

@Injectable({
  providedIn: "root"

/**
 * Service to call all the API
 */
export class ApiService {
  constructor(private http: HttpClient) {}

  /**
   * Function to handle error when the server return an error
   *
   * @param error
   */
  private handleError(error: HttpErrorResponse) {
    if (error.error instanceof ErrorEvent) {
      // A client-side or network error occurred. Handle it accordingly.
      console.error("An error occurred:", error.error.message);
    } else {
      // The backend returned an unsuccessful response code. The response body may contain clues as to what went wrong,
      console.error(
        `Backend returned code ${error.status}, ` + `body was: ${error.error}`
      );
    }
    // return an observable with a user-facing error message
    return throwError(error);
  }

  /**
   * Function to extract the data when the server return some
   *
   * @param res
   */
  private extractData(res: Response) {
    let body = res;
    return body || {};
  }

  /**
   * Function to GET what you want
   *
   * @param url
   */
  public getListOfGroup(url: string): Observable<any> {

    // Call the http GET
    return this.http.get(url, httpOptions).pipe(
      map(this.extractData),
      catchError(this.handleError)
    );
}

}

Component.ts:

import { Component, OnInit } from "@angular/core";
import { ApiService } from "../../services/api.service";

@Component({
  selector: "app-example",
  templateUrl: "./example.component.html",
  styleUrls: ["./example.component.css"]
})
export class ExampleComponent implements OnInit{

  url = "/url/path/to/your/server";

  constructor(private api: ApiService) {}

  ngOnInit() {
    this.api
      .getListOfGroup(url)
      .subscribe(
        data => {
          console.log(data);
        },
        err => {
          console.log(err);
        }
      );
  }

}

我的建议是遵循 angular 的入门指南，否则您很快就会迷失方向。 Service tutorial angular

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