在服务注入错误中注入服务（循环依赖注入）

Question

我已经开始在 Angular 5 上构建应用程序，但在将服务注入另一个服务时遇到错误问题。

下面是我的数据服务

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';

import { environment } from '../../../environments/environment';

import { AuthenticationService } from '../../services/authentication/authentication.service';

@Injectable()
export class DataService {
  private headers;
  public user: any;

  constructor(
    private http: HttpClient,
    private auth: AuthenticationService
  ) {
if (auth.loggedIn) {
      this.setHeader();
    }
  }
}

身份验证服务：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { RouterModule, Router } from '@angular/router';

import { environment } from '../../../environments/environment';
import { error } from 'selenium-webdriver';

import { DataService } from '../../services/dataservice/data.service';

@Injectable()
export class AuthenticationService {
  public loggedIn: boolean;

  constructor(
    private http: HttpClient,
    private dataservice: DataService,
    private router: Router
  ) { }
}

我在这里注入了另一个自定义服务，即 AuthenticationService。

然而，虽然运行它给了我一个错误，但我无法弄清楚为什么会抛出错误：

Uncaught Error: Can't resolve all parameters for DataService: ([object Object], ?).

在我的 app.module.ts:

中注入了提供者

providers: [
    DataService,
    AuthenticationService,
    AuthGuard
  ],

提前致谢。

Answer 1

看到你的代码后你在 DataService 和 AuthenticationService 之间有一个循环依赖，这不可能用构造函数注入

要解决这个问题，您可以这样做

export class AuthenticationService {
  public token: any;
  dataService: DataService;
  constructor(
    private http: Http,
    injector:Injector;
    private router: Router
  ) {
    setTimeout(() => this.dataService= injector.get(DataService));
  }

在服务注入错误中注入服务（循环依赖注入）

Injection of service in service giving error (Circular dependency injection)

frontend

dependency-injection

angular-services

angular