didUpdateLocations gets called, but sends wrong location

Question

I am using core locations to get the location of the iphone. I also implemented the delegate protocols to my viewcontroller files, and created a CLLocationmanager object..

When I press a button (IBAction), I want the location get updated. The delegate gets called correctly. I can see that because a NSLog messages appears with the lat/long coordinates.

But when I change the location in the IOS simulator and try to access the location again with the button, the location output I get remains the same. I have to push the button again to get the correct location. Obviously I want the location to be right the first time I push the button

This is my button that triggers the delegate:

- (IBAction)getLocation:(id)sender {


[locationManager startUpdatingLocation];
}

I have this piece of code in my viewDidLoad

locationManager.delegate = self;
locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;

This is my delegate method:

#pragma mark - CLLocationManagerDelegate 
- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
NSLog(@"didFailWithError: %@", error);
UIAlertView *errorAlert = [[UIAlertView alloc]
                           initWithTitle:@"Error" message:@"Failed to Get Your Location" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
[errorAlert show];
 }

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations{
NSLog(@"didUpdateToLocation: %@", [locations lastObject]);
CLLocation *currentLocation = [locations lastObject];


if (currentLocation != nil) {
    _longitudeLabel.text = [NSString stringWithFormat:@"%.8f", currentLocation.coordinate.longitude];
    _latitudeLabel.text = [NSString stringWithFormat:@"%.8f", currentLocation.coordinate.latitude];
   }
[locationManager stopUpdatingLocation];
}

I'm running my code in Iphone 6.1 simulator..

Answer 1

From the Apple Reference: CLLocationManager

Because it can take several seconds to return an initial location, the location manager typically delivers the previously cached location data immediately and then delivers more up-to-date location data as it becomes available.

Also answered in another stack overflow post (https://stackguides.com/questions/12858548/cllocationmanager-holds-cache-value), use the timestamp property of CLLocation to filter out older cached location objects that are returned. I chose 15 seconds to be sure to differentiate a cached object but even only a few seconds will probably suffice:

NSTimeInterval timeInterval = [[location timestamp] timeIntervalSinceNow];
if (abs((NSInteger)timeInterval) < 15)
{
    //do something
}

Answer 2

I figured it out, thanks to the comments below other answers..

I was waiting too short before calling the [locationManager stopUpdatingLocation]; method. The GPS just needed some more time..

So i just waited before doing the stopUpdatingLocation with an NSTimer. That did the job. Thanks to gWiz!

Answer 3

I think , a different location has been setup as a mock location in your Xcode , that's what the simulator shows you. Check that out first. The simulator doesn't show you your current location , it shows the location that has been setup in Xcode as a mock location. Only device can show your real location. Hope it helps.

Answer 4

This is probably because you are trying to update the UI from inside didUpdateLocations which most certainly runs on another thread than the main thread.

Change this:

if (currentLocation != nil) {
_longitudeLabel.text = [NSString stringWithFormat:@"%.8f", currentLocation.coordinate.longitude];
_latitudeLabel.text = [NSString stringWithFormat:@"%.8f", currentLocation.coordinate.latitude];
}

to this:

if (currentLocation != nil) {
    dispatch_async(dispatch_get_main_queue(), ^{
        _longitudeLabel.text = [NSString stringWithFormat:@"%.8f", currentLocation.coordinate.longitude];
        _latitudeLabel.text = [NSString stringWithFormat:@"%.8f", currentLocation.coordinate.latitude];
    });
}

Answer 5

Try This Code in iOS6 Apple wants us to use didUpdateLocations instead of didUpdateToLocation

.h file


    CLLocationManager *locationManager;


.m File

  // get the current location latitude and longitude

    // locationManager update as location
    locationManager = [[CLLocationManager alloc] init];
    locationManager.delegate = self;
    locationManager.desiredAccuracy = kCLLocationAccuracyBest;
    locationManager.distanceFilter = kCLDistanceFilterNone;
    [locationManager startUpdatingLocation];

    CLLocation *location = [locationManager location];


    locationManager.delegate=self;

    //Get user location
    [locationManager startUpdatingLocation];

    // Configure the new event with information from the location
    CLLocationCoordinate2D coordinate = [location coordinate];

    NSString *latitude = [NSString stringWithFormat:@"%f", coordinate.latitude];
    NSString *longitude = [NSString stringWithFormat:@"%f", coordinate.longitude];

    NSLog(@"dLatitude : %@", latitude);
    NSLog(@"dLongitude : %@",longitude);


- (void)locationManager:(CLLocationManager *)manager 
    didUpdateToLocation:(CLLocation *)newLocation 
           fromLocation:(CLLocation *)oldLocation{

[locations lastObject];

}

Answer 6

CLLocationManager does cache your location data. A useful approach would be to check the time interval between the updates. You will get a timestamp for each location updates. Compare the old and new location timestamps using this [newLocation.timestamp timeIntervalSinceDate:oldLocation.timestamp] and discard those updates if interval is greater than 5 or so.