是否可以同时在另一个服务中注入一个服务，反之亦然? [英] Is it possible to inject a service inside another service and vice versa at the same time?

问题描述

我在一个真实的项目中有一个真实的场景，我需要2个服务来访问彼此的属性和/或方法.我不是Angular专家，所以有可能吗?

I have a real scenario in a real project where I need 2 services to access the properties and/or methods of each other. I'm not an Angular expert so is it possible?

我尝试过，但失败了.这是我的尝试:

I have tried and it fails. Here's my attempt:

app.component.ts

app.component.ts

import { Component } from '@angular/core';
import { FirstService } from './first.service';
import { SecondService } from './second.service';

@Component({
  selector: 'my-app',
  template: '<h1>Hello world!</h1>',
  providers: [FirstService, SecondService]
})
export class AppComponent {

  constructor(public firstService: FirstService, public secondService: SecondService) {
    console.log(firstService.foo);
    console.log(secondService.bar);
  }

}

first.service.ts

first.service.ts

import { Injectable } from '@angular/core';
import { SecondService } from './second.service';

@Injectable()
export class FirstService {

  foo: string = 'abc';

  constructor(public secondService: SecondService) {
    this.foo = this.foo + this.secondService.bar;
  }

}

second.service.ts

second.service.ts

import { Injectable } from '@angular/core';
import { FirstService } from './first.service';

@Injectable()
export class SecondService {

  bar: string = 'xyz';

  constructor(public firstService: FirstService) {
    this.bar = this.bar + this.firstService.foo;
  }

}

柱塞: http://plnkr.co/edit/PQ7Uw1WHpvzPRf6yyLFd?p=preview

仅将第二个服务注入第一个服务就可以，但是一旦我将第一个服务注入第二个服务，它就会失败并向控制台抛出错误.

Just injecting the second service into the first service works fine but as soon as I inject the first service into the second service it fails and throws errors to the console.

那怎么了?

有效的解决方案应将以下内容打印到控制台日志中:

A working solution should print the following to the console log:

abcxyz
xyzabc

提前谢谢！

推荐答案

AngularJS不允许注入循环依赖项.

AngularJS does not allow injection of circular dependencies.

AngularJS的作者之一MiškoHevery建议找到共同的元素:

Miško Hevery, one of the authors of AngularJS, recommends finding the common elements:

+---------+      +---------+
|    A    |<-----|  B      |
|         |      |  |  +-+ |
|         |      |  +->|C| |
|         |------+---->| | |
|         |      |     +-+ |
+---------+      +---------+

并将其提取到第三项服务:

And extracting it to a third service:

                         +---------+
+---------+              |    B    |
|    A    |<-------------|         |
|         |              |         |
|         |    +---+     |         |
|         |--->| C |<----|         |
|         |    +---+     +---------+
+---------+

有关更多信息，请参见 MiškoHevery 中的构造函数中的循环依赖性和依赖性注入.

For more information, see Circular Dependency in constructors and Dependency Injection by Miško Hevery.

这篇关于是否可以同时在另一个服务中注入一个服务，反之亦然?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！