如何让 typescript http.get observable 等待参数返回内联？

Question

好的，所以我正在尝试调用 http.get 来等待返回参数之一 (getUserToken)，然后再调用 http.get 函数。我不想在这里将它们链接在一起，因为我的调用函数 getSomeData 返回一个 observable，然后被许多其他函数调用。

getSomeData 是需要返回 getUserToken 但 getUserToken 始终为空的，因为我没有正确地做承诺。很抱歉，我在这里没有看到解决方案。

这个函数开始调用，有很多函数可以调用，我不想在这里改变任何东西。

displayData(){
 let mySubscription = this.getSomeData();
    mySubscription.subscribe(retJson => {
      if (retJson != null && retJson !== undefined){
        console.log(retJson);
      }
    });
}

这是返回 http.get 的调用，问题在 getUserToken 中。我需要 http.get 来等待 getUserToken()。

getSomeData(){
     let temporary = this.http.get(serviceUrl, getUserToken() ).map((response: Response) => {
       return response;
  });
return temporary;
}

问题是 getUserToken 自己调用服务器，有没有办法将它包装在一个 observable 或 Promise 中，可以在 getSomeData 调用中调用和解析 http.get 内联？

getUserToken(){
     this.authenticationService.getToken()
            .subscribe(responseData => {
              if (responseData){
                let headers = new Headers({ 'Authorization': 'Bearer ' + responseData.token });
                return new RequestOptions({ headers: headers });
              }
            });
}

Answer 1

您可以通过使用switchMap 来实现。

@Injectable()
class SomeClass {
   // Constructor omitted

   public displayData():void {
      const subscription:Subscription = this.getSomeData()
         .filter(retJson => !!retJson) // Only if json is truthy
         .subscribe(console.log);
   }

   // Get the user token, then switch to the actual data
   private getSomeData():Observable<any /*Replace with correct data type*/ > {
      return this.getUserToken() // get the user token
         .switchMap(userToken => // This is the token -> switchMap basically subscribes to the getUserToken and returns another observable
            this.http.get(serviceUrl, // switch to another observable as soon as getUserToken gives a value
               new RequestOptions({headers: new Headers({...userToken})}) // optionally, add other headers here
            )
         );
   }

   private getUserToken():Observable<{authorization: string}> {
      return this.authenticationService.getToken()
        .filter(responseData => !!responseData) // only if responseData is truthy
        .map(responseData => ({'Authorization': `Bearer ${responseData.token}`})); // Map to the object representing the header header
   }

}

或者，为了让流更明显，你可以在一个方法中这样写（不推荐，只是为了让流更明显）：

const subscription:Subscription = this.authenticationService.getToken()
   .filter(responseData => !!responseData) // only if responseData is truthy
   .switchMap(userToken => // This is the token -> switchMap basically subscribes to the getUserToken and returns another observable
        this.http.get(serviceUrl, // switch to another observable as soon as getUserToken gives a value
           new RequestOptions({headers: new Headers({'Authorization': `Bearer ${responseData.token}`})}) // optionally, add other headers here
        )
    )
    .filter(retJson => !!retJson) // Only if json is truthy
    .subscribe(console.log);