Question

I have a method in my appDelegate which gets latitude and longitude and returns a string which I can use in any viewController.

AppDelegate :

-(void)StartUpdating
{    
    locManager = [[CLLocationManager alloc] init];
    locManager.delegate = self;
    locManager.distanceFilter = kCLDistanceFilterNone; // whenever we move
    locManager.desiredAccuracy = kCLLocationAccuracyHundredMeters; // 100 m
    [locManager startUpdatingLocation];
}

#pragma mark 
#pragma mark locationManager delegate methods 


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

    float latitude = newLocation.coordinate.latitude;
    strLatitude = [NSString stringWithFormat:@"%f",latitude];
    float longitude = newLocation.coordinate.longitude;
    strLongitude = [NSString stringWithFormat:@"%f", longitude];
    //[self returnLatLongString:strLatitude:strLongitude];

}

-(NSString*)returnLatLongString
{    
    NSString *str = @"lat=";
    str = [str stringByAppendingString:strLatitude];
    str = [str stringByAppendingString:@"&long="];
    str = [str stringByAppendingString:strLongitude];

    return str;
}

I am calling StartUpdating in start of application. Now in my viewController I call this method:

AppDelegate *appDelegate=[AppDelegate sharedAppDelegate];
NSString *str = [appDelegate returnLatLongString];  

But I get a crash in

str = [str stringByAppendingString:strLatitude];  

in returnLatLongString.

I know I am getting crash because there is no value in strLatitude at that time. But how can I fix this? How can I still have updated value of latitude and longitude?

Also, I don’t want to use locationManager in viewControllers. So that I can get current location in all viewControllers, I did it in appDelegate.

Answer 1

The crash might be because str is an NSString, and so therefore is not mutable. Assigning it back to itself in this case is problematic. It would be simpler just to use stringWithFormat:

NSString *str = [NSString stringWithFormat: @"lat=%@&long=%@", strLatitude, strLongitude];