错误TypeError：无法读取未定义的属性'getUsers'

Question

listuser.component.ts

import { Component, OnInit } from '@angular/core';
import { User } from 'src/app/user';
import { UserService } from 'src/app/shared_service/user.service';

@Component({
  selector: 'app-listuser',
  templateUrl: './listuser.component.html',
  styleUrls: ['./listuser.component.css']
})
export class ListuserComponent implements OnInit {
  private users:User[];
  _userService: any;
  constructor(private_userService:UserService) { }

  ngOnInit() {
    this._userService.getUsers().subscribe((users)=>{
      console.log(users);
      this.users=users;
    },(error)=>{
      console.log(error);
    })
  }

}

user.service.ts

import { Injectable } from '@angular/core';
import { Http, Response, Headers, RequestOptions} from '@angular/http';
import { Observable } from 'rxjs';
import  'rxjs/add/operator/map';
import 'rxjs-compat';
import 'rxjs/add/operator/catch';
import  'rxjs/add/observable/throw';

import { User } from '../user';

@Injectable({
  providedIn: 'root'
})
export class UserService {
  private baseUrl:string="http://localhost:8080/api";
  private headers = new Headers({'Content-Type':'application/json'});
  private options = new RequestOptions({headers:this.headers});
  _http: any;
  constructor(private_http:Http) { }

  getUsers()
  {
    return this._http.get(this.baseUrl+'/users',this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  getUser(id:Number)
  {
    return this._http.get(this.baseUrl+'/user/'+id,this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  deleteUser(id:Number)
  {
    return this._http.delete(this.baseUrl+'/user/'+id,this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  createUsers(user:User)
  {
    return this._http.post(this.baseUrl+'/users',JSON.stringify(user), this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  updateUsers(user:User)
  {
    return this._http.put(this.baseUrl+'/users',JSON.stringify(user), this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  errorHandler(error:Response){
    return Observable.throw(error||'SERVER ERROR');
  }

}

运行此..错误后： 错误TypeError：无法读取未定义的属性'getUsers'     在ListuserComponent.push ../ src / app / components / listuser / listuser.component.ts.ListuserComponent.ngOnInit（listuser.component.ts：16）     在checkAndUpdateDirectiveInline（core.js：18620）     在checkAndUpdateNodeInline（core.js：19884）     在checkAndUpdateNode（core.js：19846）     在debugCheckAndUpdateNode（core.js：20480）     在debugCheckDirectivesFn（core.js：20440）     在Object.eval [作为updateDirectives]（ListuserComponent_Host.ngfactory.js？[sm]：1）     在Object.debugUpdateDirectives [作为updateDirectives]（core.js：20432）     在checkAndUpdateView（core.js：19828）     在callViewAction（core.js：20069）

Answer 1

好像您忘记了在构造函数中的private之后和_userService之前添加空格：

constructor(private _userService:UserService) { }

Answer 2

您需要在private和_userService之间添加空格，因此

constructor(private_userService:UserService) { }

应该是

constructor(private _userService: UserService) { }

Answer 3

您的服务类别中有几个问题-

1. private和_http之间的空格
2. 删除其他声明的实例变量_http: any;

修改后的代码

import { Injectable } from '@angular/core';
import { Http, Response, Headers, RequestOptions} from '@angular/http';
import { Observable } from 'rxjs';
import  'rxjs/add/operator/map';
import 'rxjs-compat';
import 'rxjs/add/operator/catch';
import  'rxjs/add/observable/throw';

import { User } from './user';

@Injectable({
  providedIn: 'root'
})
export class UserService {
  private baseUrl:string="http://localhost:8080/api";
  private headers = new Headers({'Content-Type':'application/json'});
  private options = new RequestOptions({headers:this.headers});
  constructor(private _http:Http) { }

  getUsers()
  {
    return this._http.get(this.baseUrl+'/users',this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  getUser(id:Number)
  {
    return this._http.get(this.baseUrl+'/user/'+id,this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  deleteUser(id:Number)
  {
    return this._http.delete(this.baseUrl+'/user/'+id,this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  createUsers(user:User)
  {
    return this._http.post(this.baseUrl+'/users',JSON.stringify(user), this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  updateUsers(user:User)
  {
    return this._http.put(this.baseUrl+'/users',JSON.stringify(user), this.options).map((response:Response)=>response.json())
    .catch(this.errorHandler);

  }
  errorHandler(error:Response){
    return Observable.throw(error||'SERVER ERROR');
  }

}