为什么在注入服务后每次都调用构造函数? [英] Why is constructor call each time after injection of service?

问题描述

我使用Angular2.我在节提供程序中使用单例服务 @NgModule({}): ['MenuService'] 我使用 MenuService .

I use Angular 2. I use singleton service @NgModule({}) in section providers: ['MenuService'] I use MenuService.

MenuService 如下:@Injectable()

MenuService looks as: @Injectable()

export class MenuService {

  constructor(private userService: UserService, private i18nService: I18nService) { console.log('Called'); }
}

我将这个服务注入两个部分:

There are two components where I inject this service:

export class HeaderComponent {
  constructor(private menuService: MenuService) {}
}

export class HomeComponent {
  constructor(private menuService: MenuService) {}
}

我见过两次 console.log('Called'); ，为什么会重复调用它?

I see console.log('Called'); twice, why is it called repeatly?

推荐答案

服务在注入组件时将始终运行其构造函数，它必须设置服务的字段/属性.因此，这根本不是怪异的行为.注入的接口充当"两个对象.

A service will always run its constructor when injected in a component, it has to set the fields/props of the service. So it is not weird behaviour at all. The injected interfaces 'act' as 2 objects.

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