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 => {
    }
  ); 

}

但是我需要像这样在调用this.get_categories(1);之后调用组件内部的方法send_catagories()

组件：categories.TS

search_categories() {

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

我做错了什么？

Answer 1

您可以将回调函数添加到您的 get_category(...) 参数列表中。

例如：

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

      }, error => {
    }
  ); 

}

然后你可以像这样调用 get_category(...) ：

this.get_category(1, name_of_function);

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();
});

Answer 3

更新您的get_categories() 方法以返回总数（包装在可观察对象中）：

// 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() 返回的可观察对象（或者您可以通过链接更多的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，最后您只订阅一次。

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

obs.subscribe(
  nextCallback,
  errorCallback,
  completeCallback
);

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

obs.subscribe(nextCallback);

Answer 4

您可以将 lambda 表达式编码为 subscribe 方法的第三个参数（完成时）。这里我将departmentModel变量重新设置为默认值。

saveData(data:DepartmentModel){
  return this.ds.sendDepartmentOnSubmit(data).
  subscribe(response=>this.status=response,
   ()=>{},
   ()=>this.departmentModel={DepartmentId:0});
}

Answer 5

您也可以使用新的Subject 来做到这一点：

打字稿：

let subject = new Subject();

get_categories(...) {
   this.http.post(...).subscribe( 
      (response) => {
         this.total = response.json();
         subject.next();
      }
   ); 

   return subject; // can be subscribed as well 
}

get_categories(...).subscribe(
   (response) => {
     // ...
   }
);