Question

Let me qualify by saying I’m new to Objective-C/iOS.

My program is crashing on the uncaught exception NSInvalidArgumentException, reason: [CLLocationManager copyWithZone:]: unrecognized selector sent to instance. This seems to be a pretty common error, and best I can tell, it usually happens when something’s gone wrong memory-management wise. I’ve looked at similar questions on stackoverflow and Google, but none seem quite the same.

My application is a simple single view app. I’m trying to use the CLLocationManager class, because I want to get the user’s heading. My code:

magnetoTestViewController.h

#import <UIKit/UIKit.h>
@class CLLocationManager;

@interface magnetoTestViewController : UIViewController
@property(copy, readwrite) CLLocationManager *locManager;
@end

magnetoTestViewController.m

#import "magnetoTestViewController.h"
#import <CoreLocation/CoreLocation.h>

@interface magnetoTestViewController()
- (void)startHeadingEvents;
@end

@implementation magnetoTestViewController

@synthesize locManager = _locManager;

...

- (void)startHeadingEvents {
NSLog(@"entered startHeadingEvents()");
if (!self.locManager) {
    CLLocationManager* theManager = [[CLLocationManager alloc] init];

    // Retain the object in a property.
    self.locManager = theManager;
    self.locManager.delegate = self;
}

// Start location services to get the true heading.
self.locManager.distanceFilter = 1000;
self.locManager.desiredAccuracy = kCLLocationAccuracyKilometer;
[self.locManager startUpdatingLocation];

// Start heading updates.
if ([CLLocationManager headingAvailable]) {
    NSLog(@"Yep, the heading is available.");
    self.locManager.headingFilter = 5;
    [self.locManager startUpdatingHeading];
}
else {
    NSLog(@"*sadface*, the heading information is not available.");
}
NSLog(@"exited startHeadingEvents()");
}

- (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading {
NSLog(@"locationManagerdidUpdateHeading() was called.");
if (newHeading.headingAccuracy < 0) {
    NSLog(@"the heading accuracy is smaller than 0.  returning.");
    return;
}

// Use the true heading if it is valid.
CLLocationDirection theHeading = ((newHeading.trueHeading > 0) ?
                                  newHeading.trueHeading : newHeading.magneticHeading);
NSString* myNewString = [NSString stringWithFormat:@"the heading is %d", theHeading];
NSLog(myNewString);

}

My code is entering the startHeadingEvents method (based on my logging) but is crashing before exiting the method (based on my logging not being called). I assume copyWithZone (which is in the error) is a method of the CLLocationManager being called internally at some point. I’m sure I’m making an amateur mistake somewhere, can someone point me in the right direction?

Answer 1

Your problem is that you are using “copy” in your property for the CLLocationManager, which is a singleton – often Singletons are defined such that they throw an exception to prevent copying the single instance.

Instead, declare your property like so:

@property(nonatomic, strong) CLLocationManager *locManager;