Question

I’m new to objective-c and I’m trying to understand Xcode.

Right now, I’m in really big trouble with the following code:

AppDelegate.h

#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
#import <MapKit/MapKit.h>

@class ViewController;

@interface AppDelegate : UIResponder <UIApplicationDelegate, CLLocationManagerDelegate, MKMapViewDelegate> {

    IBOutlet UIActivityIndicatorView *activityIndicator;
    IBOutlet UITextField *locationTitleField;
    IBOutlet MKMapView *worldView;
    IBOutlet CLLocationManager *locationManager;

}

@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) UIViewController *viewController;


@end

AppDelegate.m

    #import "AppDelegate.h"

    #import "ViewController.h"

    @implementation AppDelegate

    @synthesize window = window;
    @synthesize viewController = viewController;


    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    {
        locationManager = [[CLLocationManager alloc]init];
        [locationManager setDelegate:self];
        [locationManager setDistanceFilter:kCLDistanceFilterNone];
        [locationManager setDesiredAccuracy:kCLLocationAccuracyBest];
        [worldView setShowsUserLocation:YES];


        self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
        self.window.rootViewController = self.viewController;
        [self.window makeKeyAndVisible];
        return YES;
   }

    - (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation {
     // Yes, no code here, but here's the point, where I'm getting crashes, no matter if
     // there is some code in here, or not
    }
    @end

The problem is, when I try to start the app, everything is fine. But the “didUpdateUserLocation” is really driving me nuts. I have turned on the Zombie Objects and now Xcode is telling me:

[AppDelegate mapView:didUpdateUserLocation:]: message sent to deallocated instance 0xde1b700
(lldb) 

I had (!) turned on the new ARC stuff, but I’ve turned it off, still getting the same error. As you can see, I’m not even having at least one release in my code.

Answer 1

You are misunderstanding the error message. Your AppDelegate is being sent the mapView:didUpdateUserLocation: message after it has been deallocated or the MKMapView has an invalid delegate set. It does not matter what is in this method, it just matters that the application delegate is not a valid object. You don’t say when you get this error and you don’t show enough code to tell, but your worldView is not being setup correctly or torn down correctly on quitting.

Why is your locationManager declared as an IBOutlet and then alloc/inited by you? Any setup you did for this object in your nib file will be lost by replacing it and without ARC the original will leak.