如何在Ionic 2 / Angular 2中解决一些Promise之后返回Observable？ [英] How to return Observable after some Promise get resolved in Ionic 2/Angular 2?

问题描述

我试图在成功完成Promise之后返回一个observable，但是该函数没有返回Observable。
要特定于代码，我想从存储中获取auth令牌（返回promise），然后获取该数据，然后生成一个Post请求到Api（返回Observable）。通过这样做，sublime文本在函数上给出一个错误，声明类型既不是'void'也不'any'的函数必须返回一个值
以下是我的代码，

I am trying to return an observable after a successful completion of my Promise, but that function is not returning Observable. To be specific to code, i want to fetch auth token from storage (returns promise) and after that data got fetched then generate a Post request to Api (returns Observable). By doing so, sublime text gives an error on function that "a function whose declared type is neither 'void' nor 'any' must return a value" below is my code,

logout() : Observable<any>{
  this.userData.getAuthToken().then((token)=>{
    this.token = token;
    this.headers = new Headers ({
      "X-USER-TOKEN": token
    });
    this.options = new RequestOptions ({
      headers: this.headers
    });
    var logout_url = "Api logout method";
    return this.http.post(logout_url,{},this.options)
      .map (res => res.json())
  });
}

如果我只是做一个帖子请求那么它会像这样返回

if i simply do a post request then it returns fine like this

return this.http.post(logout_url,{},this.options)
  .map (res => res.json())

但是当我尝试获取数据时，它不会从此发布请求中返回值。
任何帮助都会得到很多赞赏！提前致谢

but when i try to fetch data it do not return value from this post request. Any help will be much Appreciated! Thanks in advance

推荐答案

使用 fromPromise 将promise转换为可观察并使用 mergeMap 将HTTP响应发送到组合的observable：

Use fromPromise to convert the promise into an observable and use mergeMap to emit the HTTP response into the composed observable:

import { Observable } from 'rxjs/Observable/';
import 'rxjs/add/observable/fromPromise';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/mergeMap';

logout(): Observable<any>{
  return Observable.fromPromise(this.userData.getAuthToken()).mergeMap(token => {
    this.token = token;
    this.headers = new Headers({
      "X-USER-TOKEN": token
    });
    this.options = new RequestOptions({
      headers: this.headers
    });
    var logout_url = "Api logout method";
    return this.http.post(logout_url, {}, this.options).map(res => res.json());
  });
}

这篇关于如何在Ionic 2 / Angular 2中解决一些Promise之后返回Observable？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IT屋！