Xcode: variables populate with breakpoints but not in realtime - ios

Question

I have a function that utilizes LocationManager for iOS development. The function fulfills the very common purpose of pulling latitude and longitude from the LocationManager object and populating some method variables to build a set of directions.
Currently the method works fine on the iOS simulator when there are some specifically placed breakpoints. I will step into each step until I see that the lat and long have been populated and then continue program execution. The view is correctly altered to bring up a set of directions.
If the breakpoints are removed however, the variables are never populated and the view defaults to 0.000 for lat and longitudes.
I also see an error in one of the threads (I'm completely unfamiliar with thread based programming. This is not my app I am debugging): Thread 1: EXC_BAD_ACCESS (CODE =1, address= {some address}
Below is the function code (asdf is just the instance name for LocationManager):
(void)webViewDidFinishLoad:(UIWebView *)webView
{
asdf = [[CLLocationManager alloc] init];
asdf.delegate = self;
asdf.distanceFilter = kCLDistanceFilterNone;
asdf.desiredAccuracy = kCLLocationAccuracyHundredMeters;
[asdf startUpdatingLocation];
CLLocation *location = [asdf location];
float longitude=location.coordinate.longitude;
float latitude=location.coordinate.latitude;
NSLog(#"dLongitude : %f", longitude);
NSLog(#"dLatitude : %f", latitude);
double userLatitude = latitude;
double userLongitude = longitude;
[locationManager stopUpdatingLocation];
NSString *userLat = [NSString stringWithFormat:#"%f", userLatitude];
NSString *userLng = [NSString stringWithFormat:#"%f", userLongitude];
NSString *destinationLatitude = site.siteGPSN;
NSString *destinationLongitude = site.siteGPSW;
NSString *javascriptString = [NSString stringWithFormat:#"buildMap('%#','%#','%#','%#')",destinationLatitude, destinationLongitude, userLat, userLng];
[webView stringByEvaluatingJavaScriptFromString:javascriptString];
}

Answer 1

You're not using CLLocationManager correctly. You need to implement the CLLocationManagerDelegate. Otherwise there is no guarantee there will be a location object cached by the manager when you try to use it.
The implementation would look something like this:
- (void) locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
// handle error
}
- (void) locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
CLLocation *location = [locations lastObject];
// use location here
}
- (void) locationManager:(CLLocationManager *)manager didChangeAuthorizationStatus:(CLAuthorizationStatus)status
{
if (status == kCLAuthorizationStatusAuthorized)
{
[manager startUpdatingLocation];
}
}
Remember to call stopUpdatingLocation at the appropriate time as well (whenever you are done).
I would recommend looking at Apple's "LocateMe" sample project which provides some great starting code on how to use this protocol correctly.
https://developer.apple.com/library/ios/samplecode/LocateMe/Listings/Classes_GetLocationViewController_m.html#//apple_ref/doc/uid/DTS40007801-Classes_GetLocationViewController_m-DontLinkElementID_8

Answer 2

Location manager never gets an update as soon as you start it using startUpdatingLocation this is when the delegate methods come into action. Delegate methods are invoked only when a location update is available or the process failed for some reason.
I found that you have set:
asdf.delegate = self;
That means you are registering the current class as a handler for location updates. So you should declare the CLLocationManagerDelegate protocol in the header (.h file) of your class, like following:
#interface <# Your Class Name #> : NSObject<CLLocationManagerDelegate> // your class might have inherited from anything other than NSObject
////......
#end
Now in your implementation file (.m) implement the following methods:
-(void)locationManager:(CLLocationManager*)manager didUpdateLocations:(NSArray*)locations {
if (!locations || [locations count] == 0) {
return;
}
CLLocation* location = locations[[locations count] - 1];
if (location.horizontalAccuracy < 0) {
return;
}
float longitude=location.coordinate.longitude;
float latitude=location.coordinate.latitude;
NSLog(#"dLongitude : %f", longitude);
NSLog(#"dLatitude : %f", latitude);
double userLatitude = latitude;
double userLongitude = longitude;
//[locationManager stopUpdatingLocation]; -- dont stop it here
NSString *userLat = [NSString stringWithFormat:#"%f", userLatitude];
NSString *userLng = [NSString stringWithFormat:#"%f", userLongitude];
NSString *destinationLatitude = site.siteGPSN;
NSString *destinationLongitude = site.siteGPSW;
NSString *javascriptString = [NSString stringWithFormat:#"buildMap('%#','%#','%#','%#')",destinationLatitude, destinationLongitude, userLat, userLng];
[webView stringByEvaluatingJavaScriptFromString:javascriptString];
}
-(void)locationManager:(CLLocationManager*)manager didUpdateToLocation:(CLLocation*)newLocation fromLocation:(CLLocation*)oldLocation { //for backward compatibility
if (newLocation.horizontalAccuracy < 0) {
return;
}
float longitude=newLocation.coordinate.longitude;
float latitude=newLocation.coordinate.latitude;
NSLog(#"dLongitude : %f", longitude);
NSLog(#"dLatitude : %f", latitude);
double userLatitude = latitude;
double userLongitude = longitude;
//[locationManager stopUpdatingLocation]; -- dont stop it here
NSString *userLat = [NSString stringWithFormat:#"%f", userLatitude];
NSString *userLng = [NSString stringWithFormat:#"%f", userLongitude];
NSString *destinationLatitude = site.siteGPSN;
NSString *destinationLongitude = site.siteGPSW;
NSString *javascriptString = [NSString stringWithFormat:#"buildMap('%#','%#','%#','%#')",destinationLatitude, destinationLongitude, userLat, userLng];
[webView stringByEvaluatingJavaScriptFromString:javascriptString];
}
-(void)locationManager:(CLLocationManager*)manager didFailWithError:(NSError*)error {
NSLog(#"core location error: %#",[error localizedDescription]);
if ([error code] != kCLErrorLocationUnknown) { //when location update is not available for that time don't continue receiving updates
NSLog(#"location service will terminate now");
[manager stopUpdatingLocation];
}
}
After all these set up, your location manager would invoke the appropriate delegate method when an update is available (or failed) and you can stop your location service when you don't actually need it anymore, may be in your viewWillDisappear or dealloc methods.