iOS async task freezes - ios

Question

I have an app which does an async post to a server. Then it decodes the json and returns the message from the server. I put a few debugging log entries in my code, so I know that the response from the server, as well as the decoding of the json are instantaneous. The problem is that after the json is decoded, the async task runs for about 6 seconds before it calls the next event (Showing the popup dialog).
- (IBAction)register:(id)sender {
[self startPost]; // Starts spinner animation
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[self doPost]; // performs post
});
}
-(void)doPost
{
#try {
NSString *post =[[NSString alloc] initWithFormat:#"request=register&platform=ios&email=%#&password=%#",self.email.text,self.password.text];
//NSLog(#"PostData: %#",post);
NSURL *url=[NSURL URLWithString:#"https://site.com/api.php"];
NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
NSString *postLength = [NSString stringWithFormat:#"%d", [postData length]];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:url];
[request setHTTPMethod:#"POST"];
[request setValue:postLength forHTTPHeaderField:#"Content-Length"];
[request setValue:#"application/json" forHTTPHeaderField:#"Accept"];
[request setValue:#"application/x-www-form-urlencoded" forHTTPHeaderField:#"Content-Type"];
[request setHTTPBody:postData];
//[NSURLRequest setAllowsAnyHTTPSCertificate:YES forHost:[url host]];
NSError *error = [[NSError alloc] init];
NSHTTPURLResponse *response = nil;
NSData *urlData=[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
//NSLog(#"Response code: %d", [response statusCode]);
if ([response statusCode] >=200 && [response statusCode] <300)
{
NSString *responseData = [[NSString alloc]initWithData:urlData encoding:NSUTF8StringEncoding];
//NSLog(#"Response ==> %#", responseData);
NSData *responseDataNew = [responseData dataUsingEncoding:NSUTF8StringEncoding];
NSError* error = nil;
NSDictionary *myDictionary = [NSJSONSerialization JSONObjectWithData:responseDataNew options:NSJSONReadingMutableContainers error:&error];
if ( error ){
[self alertStatus:#"Unknown response code from server" :#"Whoops!"];
NSLog(#"Response ==> %#", responseData);
[self postDone];
}else{
if ([myDictionary[#"error"] isEqualToNumber:(#1)])
{
NSLog(#"ERROR DETECTED");
[self alertStatus:myDictionary[#"message"]:#"Whoops!"];
[self postDone];
}
else
{
[self alertSuccess];
[self postDone];
}
}
} else {
if (error) NSLog(#"Error: %#", error);
[self alertStatus:#"Connection Failed" :#"Whoops!"];
[self postDone];
}
}
#catch (NSException * e) {
NSLog(#"Exception: %#", e);
[self alertStatus:#"Registration Failed." :#"Whoops!"];
[self postDone];
}
}
-(void)startPost
{
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
self.email.enabled = false;
self.password.enabled = false;
self.confirm.enabled = false;
self.cancelButton.enabled = false;
}
- (void) alertStatus:(NSString *)msg :(NSString *)title
{
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title
message:msg
delegate:self
cancelButtonTitle:#"Ok"
otherButtonTitles:nil, nil];
[alertView setTag:0];
[alertView show];
}
- (void) alertSuccess
{
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Success!"
message:#"You have been successfully registered."
delegate:self
cancelButtonTitle:#"Ok"
otherButtonTitles:nil, nil];
[alertView setTag:1];
[alertView show];
}
-(void)postDone
{
self.registerButton.hidden = false;
self.spinner.hidden = true;
self.loadingText.hidden = true;
//[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
self.email.enabled = true;
self.password.enabled = true;
self.confirm.enabled = true;
self.cancelButton.enabled = true;
}
- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{if (alertView.tag == 1)
{
[self dismissViewControllerAnimated:YES completion:nil];
}}
The alertStatus and alertSuccess functions just pop up a message box briefly.
When I run the code, I purposefully enter bad information so the log says "ERROR DETECTED". The problem is that it takes another 6 seconds before anything happens after that.

Answer 1

After you have called:
NSData *urlData=[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
and obtained the data, you should switch back to the main thread to use it. This is because all UI updates must be done on the main thread.
So, all that code after you get the data should be moved to a new method and called as:
dispatch_async(dispatch_get_main_queue(), ^{
[self handleData:urlData withResponse:response error:error];
}
And you should also put the exception catch code inside dispatch_async(dispatch_get_main_queue(), ^{ because you try to update the UI there too...