how to display UIAlertView inside sendAsynchronousRequest's completionHandler? - ios

Question

I am developing a login application. I have a registration view, I'm using sendAsynchronousRequest to send registration request.When I received a data back I want to show alert view displaying the registration if valid. Now my problem is When I received a data back the UI get blocked until alert view display.
why is that happen and how could I fix it ?
check the the code snippet:
[NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
error = connectionError;
NSMutableDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil ];
if ([dic count] == 1) {
[dic valueForKey:#"RegisterUserResult"];
UIAlertView *alertview = [[UIAlertView alloc] initWithTitle:#"Registration" message:[dic valueForKey:#"RegisterUserResult"] delegate:self cancelButtonTitle:#"cancel" otherButtonTitles:nil];
[alertview show];
}else {
UIAlertView *alertview = [[UIAlertView alloc] initWithTitle:#"Registration" message:[dic valueForKey:#"ErrorMessage"] delegate:self cancelButtonTitle:#"cancel" otherButtonTitles:nil];
[alertview show];
}
[self printData:data];

Answer 1

You try to perform UI operations on non-main thread because completion block executes on you custom operation queue.
You need to wrap all UI calls in
dispatch_async(dispatch_get_main_queue(), ^{
......
});
within custom operation queue non-main threads.
So, in your code any call for UIAlertView will looks like
dispatch_async(dispatch_get_main_queue(), ^{
UIAlertView *alertview = [[UIAlertView alloc] initWithTitle:#"Registration" message:[dic valueForKey:#"RegisterUserResult"] delegate:self cancelButtonTitle:#"cancel" otherButtonTitles:nil];
[alertview show];
});
If you have no heavy operations in your completion handler you can dispatch it on main thread directly setting queue to [NSOperationQueue mainQueue]
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {...}];