Understanding Observables and Observer in Angular 2

Question

Below is a method in my Angular 2 service which returns an "Observable" of Array of "Category" objects.

// Get all categories
GetCategories():Observable<Array<Category>> {       

      return this.http.get('./categories')
                 .map(data => data.json())
                 .catch(this.handleError);;                                        

}

As per my understanding , the array of "Category" objects returned by the above service method can be accssed from Component code in 2 ways

Style 1

     this.appService.GetCategories().subscribe({next: (data) => {
                                                                    this.appService.categories = data;
                                                                    this.categories = this.appService.categories
                                                                },
                                                error: (err) => {
                                                                    this.toaster.error(err);
                                                                }                
     });

Style 2

    this.categories$ = this.appService.GetCategories(); // returns an Observable<Array<Category>>

and access the data in template using "async" pipe.

Now my question is,in case of style 1, I was able to display an error alert in case of an error , but if I go with style 2 , how will I able to display a custom error alert.

You can have more than one subscriber to `this.categories$` - one could be doing the error handling separately from the resolution in the template. — jonrsharpe, Dec 26 '16 at 17:37
http://stackoverflow.com/questions/38230152/error-handling-with-angular2-async-pipe — eko, Dec 26 '16 at 17:37
That will however send the HTTP request twice, AFAIK, unless you share the observable before subscribing to it. — JB Nizet, Dec 26 '16 at 17:39

Understanding Observables and Observer in Angular 2

0 Answers0