ios - UIAlertView takes too long when using inside NSURLSession

Question

I am using NSURLSession to get some information from my server. After i get the data, i show it in a UIAlertView, but it takes too long to show. I print the data with the NSLog and it prints it almost instantly... So what is happening? Does the method dataTaskWithRequest is not asynchronous? Why it takes so much time to pop up the alert view?

NSURLSession *session;
session = [NSURLSession sharedSession];
NSURL * url = [NSURL URLWithString:[DRESSABLE_IP stringByAppendingString:@"index.php"]];
NSMutableURLRequest * urlRequest = [[NSMutableURLRequest alloc] initWithURL:url cachePolicy:CONNECTION_CACHEPOLICY  timeoutInterval:CONNECTION_TIMEOUT];
[urlRequest setHTTPMethod:@"POST"];
NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:urlRequest 
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        NSString *total = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
        [[[UIAlertView alloc] initWithTitle:@"Title" message:total delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil] show];
 }];

Answer 1

All UI activity must be done in the main queue.

NSURLSession *session;
session = [NSURLSession sharedSession];
NSURL * url = [NSURL URLWithString:[DRESSABLE_IP stringByAppendingString:@"index.php"]];
NSMutableURLRequest * urlRequest = [[NSMutableURLRequest alloc] initWithURL:url cachePolicy:CONNECTION_CACHEPOLICY  timeoutInterval:CONNECTION_TIMEOUT];
[urlRequest setHTTPMethod:@"POST"];
NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:urlRequest 
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        NSString *total = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
dispatch_async(dispatch_get_main_queue(),^{
        [[[UIAlertView alloc] initWithTitle:@"Title" message:total delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil] show];
});
 }];