Displaying error messages after modal dismissal - ios

Question

So just like the question suggests, I'm trying not to freeze up the UI after the user sends some data to the server. In my case, they're possibly sending a lot of data and server side I have to do a foreach loop for multiple queries.
While all that is happening, I don't want the user to wait for a response so I'm dismissing the modal VC after "Send" is clicked. The data still gets inserted into the database but what if there's an error? Right now I'm showing a UIAlertView after the modal VC is dismissed but I get a bad access error. What's the best way of showing an error?
- (void)send:(id)sender{
if ([[Data sharedInstance].someData objectForKey:#"time"] != NULL) {
[self dismissViewControllerAnimated:YES completion:^(){
NSMutableDictionary *paramDic = [NSMutableDictionary new];
[paramDic setValue:[[Data sharedInstance].someData objectForKey:#"oneArray"] forKeyPath:#"oneArray"];
[paramDic setValue:[NSArray arrayWithObjects:[[[Data sharedInstance].someData objectForKey:#"two"] valueForKey:#"Name"], [[[Data sharedInstance].someData objectForKey:#"two"] valueForKey:#"State"], [[[Data sharedInstance].someData objectForKey:#"two"] valueForKey:#"Country"], nil] forKeyPath:#"twoArray"];
[paramDic setValue:[[[Data sharedInstance].someData objectForKey:#"three"] stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding] forKeyPath:#"three"];
[paramDic setValue:[[NSUserDefaults standardUserDefaults] valueForKey:#"username"] forKey:#"username"];
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:paramDic options:NSJSONWritingPrettyPrinted error:nil];
NSURL *url = [NSURL URLWithString:#"http://localhost/myapp/handleData.php"];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:#"POST"];
[request setValue:#"application/json" forHTTPHeaderField:#"Content-Type"];
NSString *length = [NSString stringWithFormat:#"%d", jsonData.length];
[request setValue:length forHTTPHeaderField:#"Content-Length"];
[request setValue:#"json" forHTTPHeaderField:#"Data-Type"];
[request setHTTPBody:jsonData];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
if (![httpResponse statusCode] == 200 || ![[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding] isEqualToString:#"success"]) {
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:#"Error" message:#"Problem on the server. Please try again later." delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
}
}];
}];
}
That's how I'm doing it now...what's a better way?

Answer 1

The above answer is valuable. But I think this is what causes the problem.
Change:
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:#"Error" message:#"Problem on the server. Please try again later." delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
To:
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:#"Error" message:#"Problem on the server. Please try again later." delegate:nil cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
Hope this helps.

Answer 2

I'm thinking the issue has to do with your nested completion blocks. Because you place your web service call in the modal dismissal completion block, by the time it finishes and starts to execute your URL completion block, the class/controller in charge of that block has already been forgotten/destroyed/deallocated/whatever. At the very least, the view no longer exists where you're trying to present your alert view. You've listed self as the delegate of that alert view, but self doesn't exist anymore.
Try this first: instead of trying to display your alert on a no-longer-in-memory view from a background thread (big no-no even if the view still existed), try posting a notification to the main thread that you can pick up elsewhere in your app (such as your root view controller) and present the alert from there:
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
if (![httpResponse statusCode] == 200 || ![[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding] isEqualToString:#"success"]) {
dispatch_async(dispatch_get_main_queue(),^{
// observe this notification in root view controller or somewhere
// that you know will be in memory when it fires
[[NSNotificationCenter defaultCenter] postNotificationName:#"ErrorAlert"
object:nil
userInfo:imageDict];
});
}
}];
If that still doesn't work because the app has discarded your completion block when the view was dismissed, you will need to create a separate class that is in charge of sending this web service request instead of doing it all directly in the completion block. But still, remember to present your alert on the main thread :)