为什么每次注入服务后都会调用构造函数?

问题描述

我使用 Angular 2.我在部分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 看起来像:@Injectable()

MenuService looks as:@Injectable()

export class MenuService {

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

我在两个组件中注入了此服务:

There are two components where I inject this service:

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

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

我看到console.log('Called');两次，为什么会重复调用?

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/道具.所以这根本不是奇怪的行为.注入的接口充当"2 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.

这篇关于为什么每次注入服务后都会调用构造函数?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！