Angular subscribe() 返回未定义

Question

如果我的控制台显示以下内容，我该如何解决 app.component 的 subcribe() 问题：错误类型错误：无法读取属性 'subscribe'未定义的在 AppComponent.push../src/app/app.component.ts.AppComponent.ngOnInit

data.service:

   import { Injectable } from '@angular/core';
   import { Http, Response } from '@angular/http';

   import { Injectable } from '@angular/core';
   import { Observable, Subject, ReplaySubject } from 'rxjs';
   import { from, of, range } from 'rxjs/create';
   import { map, filter, switchMap } from 'rxjs/operators';


 @Injectable({
    providedIn: 'root'
    })


export class DataService {

  constructor(private http: Http) { }

  fetchData(){
    this.http.get('assets/ninjas.json').pipe(
     map((res) => return res.json()))}}

app.components:

import { Component } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})

export class AppComponent {
  title = 'app';
  ninjas = [];

  constructor(private newService: DataService){ }

  ngOnInit(){
   this.newService.fetchData().subscribe(
    (data) => this.ninjas = data;
   );
  }
 }

Answer 1

Return 您服务中的可观察对象，

 fetchData(){
    return this.http.get('assets/ninjas.json').pipe(
     map((res) => return res.json()))}}

Answer 2

只需删除 'pipe'，您不需要它：

fetchData(){
    return this.http.get('assets/ninjas.json');
}

Angular subscribe() 返回未定义

Angular subscribe() returning undefined

service

http

subscribe

angular