Question

尝试返回Observable。我应该怎么做呢？

  get(url) : Observable<any> {
    let headers = new Headers();
    this.SetAuthorizationHeader(headers).then(() => { // Resolving a promise
      return this.http.get(url, { // <-- I need to return the Observable from here
          headers: headers
      });
    });
  }

消费（不工作）：

public GetInfo() : Observable<any> {
    return this.authHttpClient.get(this.constants.api_base + "/users/info")
        .map((res: Response) => res.json());
}

谢谢！

Answer 1

您只需要返回this.SetAuthorizationHeader(headers)方法，因此在解析SetAuthorizationHeader方法时，它会返回http.get来电可观察。

在这里，您需要从get方法返回类型中删除Observable<any>，实际上它将返回Promise对象。

<强>代码

get(url) : any {
    let headers = new Headers();
    //return promise here to continue chain & return inner observable.
    return this.SetAuthorizationHeader(headers).then(() => { // Resolving a promise
      return this.http.get(url, { // <-- I need to return the Observable from here
          headers: headers
      });
    }).map(data => data.json());
}

<强>消耗

public GetInfo() : any { //here also it will be any, because you are returning `authHttpClient.get` at the end
    return this.authHttpClient.get(this.constants.api_base + "/users/info"));
}

获取信息消费

this.user.GetInfo().then(obs => 
    obs.subscribe(
      user => { alert(JSON.stringify(user)); }, 
     (error) => { alert(JSON.stringify(error)); }
);

Answer 2

Pankaj Parker的作品，但返回类型为Promise<Observable<any>>。这就是为什么需要额外的.then((obs) => obs.subscribe(...))。

您可以通过将您的承诺转换为可观察对象来避免这种情况，并使用concatMap将两者结合起来。

使用concatMap可以控制observable的顺序，因此在http请求之前会发出设置授权头的observable。

<强>代码

  get(url): any {
    let headers = new Headers();
    //transform promise to observable
    const authHeaderObservable = Observable.from(this.SetAuthorizationHeader(headers));

    return authHeaderObservable.concatMap(() => { //return the outer observable
      return this.http.get(url, { // <-- I need to return the inner Observable from here
        headers: headers
      }).map(data => data.json());
    })
  }

<强>消耗

public GetInfo() : any { //here also it will be any, because you are returning `authHttpClient.get` at the end
    return this.authHttpClient.get(this.constants.api_base + "/users/info"));
}

获取信息消费

this.user.GetInfo().subscribe(
      user => { alert(JSON.stringify(user)); }, 
     (error) => { alert(JSON.stringify(error)); }
);

在已解决的承诺中返回Observable

2 个答案: