Question

I am trying to run a following Function

+(NSString *)responseFromQuery:(NSString *) queryString
{
    __block NSString *response;
    __block NSError *err = nil;

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0),^{
        response = [NSString stringWithContentsOfURL:[NSURL URLWithString:queryString] encoding:NSUTF8StringEncoding error:&err];

        dispatch_async(dispatch_get_main_queue(), ^{

            NSLog(@"%@",response);
             if (err != nil)
             {
                UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Alert!"
                                                                    message:@"An Error has occurred" delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil];

                [alertView show];
                 return response;// = @"Error";
              }

            });
        });
   // return response;
}

I want to pass the value of response after executing the block, however instead it runs the last return first , how can i make the return expression within block to run.
I am using this function in an NSObject Class
According to the debugging it never runs the dispatch_async queue.

Right now if i return it gives me error "Control may reach at the end of non void block"

Answer 1

To fully understand the implementation and working of blocks in objective c i think you should look into the following link, it explains quite a lot and it is put really simply.

Objective C Blocks – Simple Understanding