Updating Interface from Result of NSURL Request - iphone

Question

I have an app that updates the interface depending on the result of a NSURL request. I have set it up so that the request is fired when my app comes into the foreground, and only if the current view controller is called "ProfileViewController".
My problem is that the interface locks up for a few seconds every time I bring the app back from the background. I am trying to fully understand main/background threads, but am not sure what I can do to make the app remain responsive while the NSURL check is being performed. Any assistance would be great! Thanks!
In my View Did Load Method:
-(void)viewDidLoad {
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(appReturnsActive) name:UIApplicationDidBecomeActiveNotification
object:nil];
//additional code
}
Then in my App Returns Active Method:
- (void)appReturnsActive {
[myTimer invalidate];
myTimer = nil;
//ONLY WANT TO PERFORM THE UPDATE IF VIEWING THE PROFILE VIEW CONTROLLER
UIViewController *currentVC = self.navigationController.visibleViewController;
NSString * name = NSStringFromClass([currentVC class]);
if ([name isEqualToString:#"ProfileViewController"]) {
[activityIndicator startAnimating];
[activityIndicatorTwo startAnimating];
locationManagerProfile.delegate = self;
locationManagerProfile.desiredAccuracy = kCLLocationAccuracyBest;
[locationManagerProfile startUpdatingLocation];
}
}
Finally, in my Did Update Location Method, I get the distance between the user and the location. If the result is equal to 1, then I update the Interface to show different buttons. This is where the interface freezes up:
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation
*)newLocation fromLocation:(CLLocation *)oldLocation {
CLLocation *currentLocation = newLocation;
if (currentLocation != nil) {
[self performSelectorOnMainThread:#selector(buttonUpdate:)
withObject:NULL waitUntilDone:NO];
}
}
New Method:
-(void)buttonUpdate {
NSString *userLongitude =[NSString stringWithFormat:#"%.8f",
currentLocation.coordinate.longitude];
NSString *userLatitude = [NSString stringWithFormat:#"%.8f",
currentLocation.coordinate.latitude];
[locationManagerProfile stopUpdatingLocation];
NSString *placeLatitude = [[NSUserDefaults standardUserDefaults]
stringForKey:#"savedLatitude"];
NSString *placeLongitude = [[NSUserDefaults standardUserDefaults]
stringForKey:#"savedLongitude"];
NSString *distanceURL = [NSString
stringWithFormat:#"http://www.website.com/page.php?
lat1=%#&lon1=%#&lat2=%#&lon2=%#",userLatitude, userLongitude, placeLatitude,
placeLongitude];
NSData *distanceURLResult = [NSData dataWithContentsOfURL:[NSURL
URLWithString:distanceURL]];
NSString *distanceInFeet = [[NSString alloc] initWithData:distanceURLResult
encoding:NSUTF8StringEncoding];
if ([distanceInFeet isEqualToString:#"1"])
{
UIBarButtonItem *btnGo = [[UIBarButtonItem alloc] initWithTitle:#"Button 1"
style:UIBarButtonItemStyleBordered target:self
action:#selector(actionTwo)];
self.navigationItem.rightBarButtonItem = btnGo;
UIBarButtonItem *btnGoTwo = [[UIBarButtonItem alloc] initWithTitle:#"Button
Two" style:UIBarButtonItemStyleBordered target:self
action:#selector(actionOne)];
self.navigationItem.rightBarButtonItem = btnGoTwo;
self.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:btnGo,
btnGoTwo, nil];
}
}

Answer 1

Your CoreLocation delegate methods (e.g. "didUpdateToLocation", etc.) are all happening in the background, on secondary threads, while everything UI-related needs to happen on the main thread.
To fix your problem, you should modify your UI on the main thread. One of the handy foundation API's you can use is:
performSelectorOnMainThread:withObject:waitUntilDone:
To fix your problem, move your button-creating code into a separate method and call that new method via "performSelectorOnMainThread" from the old (being called on a separate thread via the CoreLocation delegate protocol) and you should be good to go.

Answer 2

NSData *distanceURLResult = [NSData dataWithContentsOfURL:[NSURL
URLWithString:distanceURL]];
is a synchronous call. It means your code will wait for the result of the network call to continue. You should make an Asynchronous request, with NSURLConnection (http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSURLConnection_Class/Reference/Reference.html) or AFNetworking.