App crashes on slow InternetConnection - objective-c

Question

I am getting data from server in applicationDidBecomeActive method.When net connection is too slow app keep crashing.I do not know how to handle this problem.any help will be appreciated.thanks in advance.
NSString *post =[[NSString alloc] initWithFormat:#"=%##=%#",myString,acMobileno];
NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:#"http:///?data=%#&no=%#",myString,acMobileno]];
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 setHTTPBody:postData];
NSError *error1 = [[NSError alloc] init];
NSHTTPURLResponse *response = nil;
NSData *urlData=[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error1];
NSString *string;
if ([response statusCode] >=200 && [response statusCode] <300)
{
string = [[NSString alloc] initWithData:urlData encoding:NSMacOSRomanStringEncoding];
}

Answer 1

It's probably crashing because the connection has started downloading, but it hasn't finished therefore allowing the complier to pass your if statement, which would inevitably give a nil urlData parameter.
To fix this, you should be checking to see if there is an error, and then the response headers for the download. Also, I recommend running this operation on a background thread so that it doesn't block the user experience - at the moment, the app will have a delayed launch depending on the size of your file, and the user's download speed.
NSError *error1 = nil;
NSHTTPURLResponse *response = nil;
NSData *urlData=[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error1];
NSString *string = nil;
if (error != nil && ([response statusCode] >=200 && [response statusCode] <300)){
string = [[NSString alloc] initWithData:urlData encoding:NSMacOSRomanStringEncoding];
}
else {
NSLog(#"received error: %#", error.localizedDescription);
}
For a background thread, run the above code in a dispatch_async statement, or use -sendAsynchronousRequest: instead of -sendSynchronousRequest.
Alternatively, as #Viral said, it is possible that the request is taking too long, and the app is hanging as a result of the synchronous request not finishing before the UI should have been loaded.

Answer 2

Most probably, it's due to synchronous call in Application's delegate method. It is taking too much time to load the UI (As internet connection is slow and you are calling the web service on main thread); and therefore OS thinks your App has hanged due to unresponsive UI and crash the App itself.
Just for debugging purpose, try the same code in your FirstViewController's viewDidAppear method. It should work fine there. And if it is so, you need to change your call to somewhere else (also, preferably in some background thread, OR Async).
EDIT: Though, If it works elsewhere, you need to change the call as Async OR on background thread for smoother UX.