Angular 2：从订阅 http.post 获得响应后如何调用函数

Question

从http post请求中获取数据后，我需要调用一个方法

服务：request.service.TS

 get_categories(number){
 this.http.post( url, body, {headers: headers, withCredentials:true})
    .subscribe(
      response => {
        this.total = response.json();

      }, error => {
    }
  );

}

组件：categories.TS

 search_categories() {

this.get_categories(1);
//I need to call a Method here after get the data from response.json() !! e.g.: send_catagories();
}

仅当我更改为：

服务：request.service.TS

 get_categories(number){
 this.http.post( url, body, {headers: headers, withCredentials:true})
    .subscribe(
      response => {
        this.total = response.json();
        this.send_catagories(); //here works fine

      }, error => {
    }
  );

}

但是我需要在调用后调用方法 send_catagories() 在组件内部 this.get_categories(1); 像这样

组件：categories.TS

 search_categories() {

this.get_categories(1);
this.send_catagories(response);
}

我做错了什么？

原文由 Louise 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

更新您的 get_categories() 方法以 返回 总数（包装在 observable 中）：

 // Note that .subscribe() is gone and I've added a return.
get_categories(number) {
  return this.http.post( url, body, {headers: headers, withCredentials:true})
    .map(response => response.json());
}

在 search_categories() 中，您可以订阅 get_categories() 返回的 observable（或者您可以通过链接更多 RxJS 运算符来继续对其进行转换）：

 // send_categories() is now called after get_categories().
search_categories() {
  this.get_categories(1)
    // The .subscribe() method accepts 3 callbacks
    .subscribe(
      // The 1st callback handles the data emitted by the observable.
      // In your case, it's the JSON data extracted from the response.
      // That's where you'll find your total property.
      (jsonData) => {
        this.send_categories(jsonData.total);
      },
      // The 2nd callback handles errors.
      (err) => console.error(err),
      // The 3rd callback handles the "complete" event.
      () => console.log("observable complete")
    );
}

请注意，您最后 只订阅 ONCE 。

就像我在评论中所说的那样，任何 observable 的 .subscribe() 方法都接受 3 个这样的回调：

 obs.subscribe(
  nextCallback,
  errorCallback,
  completeCallback
);

它们必须按此顺序通过。您不必通过所有三个。很多时候只实现了 nextCallback ：

 obs.subscribe(nextCallback);

原文由 AngularChef 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

get_categories(number){
 return this.http.post( url, body, {headers: headers, withCredentials:true})
      .map(t=>  {
          this.total = t.json();
          return total;
      }).share();
  );
}

然后

this.get_category(1).subscribe(t=> {
      this.callfunc();
});

原文由 pixelbits 发布，翻译遵循 CC BY-SA 3.0 许可协议