Http failure response for (unknown url): 0 Unknown Error

[olabanji tajudeen]

Hi everyone I am new to angular. My first project trying to get data from an API throws this error "Http failure response for (unknown url): 0 Unknown Error". Please I want to know what could have been causing this error. Thanks in advance for your response.

[Sander Elias]

Hi Olebanji,

Error 0 is what you get when de request does not go out. Most common cause of this is that CORS is not configured correctly on the server. Let me rephrase that to: In 98% of the cases, this is a server side issue. Even in the case postman works.

look up CORS

Regards

Sander

[olabanji tajudeen]

Thanks Sander for the response. I am using asp.net web api as the back end server I configured my CORS I still get the same error

[Sander Elias]

Hi Olebanji,

Open up the network tab and look at the details in there. Also, make sure you look at what kind of request it is that fails. I suspect your server is erroring out on the "options" request.

Regards

Sander

[olabanji tajudeen]

Thanks sander I did not configure CORS very well on the server. Now I have fixed it and its returning response but the response is not showing on the page I had to inspect the code and found out it returned object in 4 places. I think I will have to serialize it to the object I have on the client. I dont know how to go about that. I have "Category" class on the server I created "Category" with the same fields in my angular like this 

export class Category {

  id: number;

  name: string;

}

I called the server like this 

getCategories (): Observable<Category[]> {

  return this.http.get<Category[]>('http://localhost:56757/api/product/categories')

    .pipe(

      tap(categories` => this.log(`fetched categories`)),

      catchError(this.handleError('getCategories', []))

    );

}

HTML :

 <ul>

  <li *ngFor="let cat of categories">

    <span class="badge">{{cat.id}}</span> {{cat.name}}

  </li>

</ul>

On Monday, November 20, 2017 at 1:47:03 PM UTC+1, olabanji tajudeen wrote:

[Sander Elias]

Hi Olebanji,

Your code doesn't show me if you are injecting http, or httpclient. HttpClient does the json unrwapping.

Given what I know of java backends, you might need to unwrap it a bit more. I think what you get is something like:

interface javaResponse {

   Category: {
      id: number;
      name: string;

   }[]
}

that's not the actual code, but it should get you going.

Regards

Sander

[olabanji tajudeen]

Thanks Sander I think I need to update to version 5.0

[olabanji tajudeen]

Hi Sander I'm still on this issue now i'm using angular 5.0 still not seeing the data returned, But I know data is returning because I use *ngfor on <li> tag it repeating the number of data in my database Pls I need help on this I have been on it for the past 3 weeks

On Friday, November 24, 2017 at 3:51:40 AM UTC+1, Sander Elias wrote: