Angular2 全球服务商 [英] Angular2 global service provider

问题描述

/app
        - app.component.ts 
        - app.component.html (hide/show: menu bar)
        - app.global.service.ts (Public varible LoginSuccess:boolean)
        - main.ts
        /student
            - student.ts
            - student.service.ts
            - student.component.ts
            - student.component.html
        /security
            - login.component.ts (LoginSuccess = true)
            - login.component.html

在我的 Angular2 应用程序中，我有一个简单的需求，我想根据登录成功显示隐藏菜单栏.为此，我创建了一个只有 LoginSuccess 布尔变量的服务，我将在登录组件上设置它，并将在 app.component.html 上用于 [hidden]=LoginSuccess 导航标签.

In my application of Angular2, I have a simple need where I want to show hide menu bar based on login success. For that I created a service which just have a LoginSuccess boolean varilable, which I would set on login component and will use on app.component.html for [hidden]=LoginSuccess nav tag.

我面临的问题是，即使在通过 app.component.ts & 的 constructor 注入 app.global.service.ts 之后login.component.ts 值不是持久化的，每个构造函数都会创建 app.global.service.ts 的新对象.

Problem I am facing is, even after injecting app.global.service.ts thru constructor of app.component.ts & login.component.ts value is not persisting and each constructor creating new object of app.global.service.ts.

问题:我如何通过服务实现跨应用程序保持单个值.在 Angular2 文档的某个地方，我确实读到可注入服务是单例的.

Question: How can I achieve to persist single value across application thru service. Somewhere in Angular2 docs, I did read that Injectable service is singleton.

推荐答案

你应该在引导时提供 GlobalService，而不是为每个组件提供:

You should provide GlobalService at bootstrap, and not for each component:

bootstrap(AppComponent, [GlobalService])

@Component({
  providers: [], // yes
  // providers: [GlobalService], // NO.
})
class AppComponent {
  constructor(private gs: GlobalService) {
    // gs is instance of GlobalService created at bootstrap
  }
}

这样 GlobalService 将是一个单例.

This way GlobalService will be a singleton.

有关更高级的方法，请参阅此答案.

For more advanced approach see this answer.

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