Why my delegate method never gets called?

Question

I was following these question and tutorials:

• fetching data with get post methods
• sending http get and post from cocoa
• nsurlconnection basics for beginners
• sending an http post request on ios
• how to hanlde multiple delegates

But I am still missing something. My delegate method

- (void)connectionDidFinishLoading:(NSURLConnection *)connection

gets called all the time, takes a little bit time and I guess its because of internet speed, but the method

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData*)data 

never gets called. What am I missing? Please help me.

My code:

-(void)loadDataBase{
    NSString *post = [NSString stringWithFormat:@"advnr=123"];
    NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
    NSString *postLength = [NSString stringWithFormat:@"%lu",(unsigned long)[postData length]];
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://thewebsite.abc/interface.php"]]];
    [request setHTTPMethod:@"POST"];
    [request setValue:postLength forHTTPHeaderField:@"Content-Length"];
    [request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    [request setHTTPBody:postData];
    NSURLConnection *conn = [[NSURLConnection alloc]initWithRequest:request delegate:self];
    //return @"";
}

#pragma mark -
#pragma mark NSURLConnection delegates

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData*)data {
    NSLog(@"Success"); // never gets executed
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"didFinished");
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"FAILED");
}

Answer 1

I suspect that there is truly no data being returned (either because of some web service error or incorrectly prepared request).

You can use Charles to observe the request and the response to confirm this, if you'd like. BTW, Charles, or any tool like this, is a useful weapon to add to your arsenal, as it greatly simplifies diagnosing HTTP problems, isolating network related issues from client-side programming issues.

Regardless, if you get these sorts of errors, you will often get a non-200 statusCode returned by the server. See list of HTTP status codes.

You can verify this by also implementing didReceiveResponse and inspect the header of the response:

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse*)response {
    if ([response isKindOfClass:[NSHTTPURLResponse class]]) {
        int statusCode = [(NSHTTPURLResponse *)response statusCode];
        if (statusCode != 200) {
            NSLog(@"Status code = %ld; response = %@", (long)statusCode, response);

            // handle this error however you'd like
        }
    }

    // temporarily, you might even want to log the whole `response` regardless of the status code
    NSLog(@"%s: %@", __PRETTY_FUNCTION__, response);
}