Angular2 - 订阅服务变量的变化 [英] Angular2 - subscribe to Service variable changes

问题描述

我有一个认证服务，使身份验证的变量为真或假。

  checkAuthentication（）{
  this._authService.getAuthentication（）
    .subscribe（价值=＆GT; this.authenticated =值）;
}
 

在 this.authenticated 已经改变了价值我如何执行一个功能？ ngOnChanges不拿起变化。

解决方案

要保持验证服务，你可以用组件之间共享
BehaviorSubject ，这是值在不同的地方，检查认证，它的订阅（）方法对变化做出反应......

 类AuthService {
  公开验证=新BehaviorSubject（NULL）;
  getAuthentication（）{
    this._http.get（'/身份验证）
      .MAP（响应= GT; response.json（））
      .MAP（JSON =＆GT;布尔（JSON））//或任何检查你需要...
      .subscribe（（价值：布尔）=＆GT; this.authenticated.next（值））
  }
}类Component {
  constuctor（私人_authService：AuthService）{
    //只检查一次，即使组件
    //破坏并重新构建
    如果（this._authService.authenticated.value ===空）
      this._authService.getAuthentication（）;
  }  的onSubmit（）{
    如果（！this._authService.authenticated.value）
      抛出新的错误（你验证！）
  }
}
 

  

如何当 this.authenticated 已经改变了我的价值执行一个功能？

  this._authService.authenticated
   .subscribe（（价值：布尔）=＆GT;的console.log（值））
 

I have an authentication service that makes the authenticated variable equal to true or false.

checkAuthentication(){
  this._authService.getAuthentication()
    .subscribe(value => this.authenticated = value);
}

How do I execute a function when this.authenticated has changed value? ngOnChanges is not picking up the change.

解决方案

To keep authenticated in service and share it between components you can use BehaviorSubject, it's value to check authentication in different places, and it's subscribe() method to react on change...

class AuthService {
  public authenticated = new BehaviorSubject(null);
  getAuthentication() {
    this._http.get('/authenticate')
      .map(response => response.json())
      .map(json => Boolean(json)) // or whatever check you need...
      .subscribe((value: boolean) => this.authenticated.next(value))
  }
}

class Component {
  constuctor(private _authService: AuthService) {
    // Only check once even if component is 
    // destroyed and constructed again
    if (this._authService.authenticated.value === null)
      this._authService.getAuthentication();
  }

  onSubmit(){
    if (!this._authService.authenticated.value)
      throw new Error("You are authenticated!")
  }
}

How do I execute a function when this.authenticated has changed value?

  this._authService.authenticated
   .subscribe((value: boolean) => console.log(value))

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