MapKit Custom Annotations

Question

I have some questinos regarding iOS6 mapkit. I tried to create a simple application that shows my current location and adds custom annotations to my MapView control . This is my code:

@interface MapViewAnnotation : NSObject<MKAnnotation>{}

@property (nonatomic, copy) NSString *title;
@property (nonatomic, readonly) CLLocationCoordinate2D cordinate;

- (id) initWithTitle:(NSString *) t coordinate:(CLLocationCoordinate2D) c;

@end

And the implementation:

#import "MapViewAnnotation.h"
@implementation MapViewAnnotation
@synthesize title;
@synthesize coordinate;
- (id) initWithTitle:(NSString *) t coordinate:(CLLocationCoordinate2D) c{
    self = [super init];
    self.title = t;
    self.coordinate = c;
    return self;
}
@end

And this is UIViewController :

#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
#import <MapKit/MapKit.h>
@interface ViewController : UIViewController <CLLocationManagerDelegate,MKMapViewDelegate>{}

@property (nonatomic, strong) IBOutlet MKMapView *mapView;
@property (nonatomic, strong) CLLocationManager *locationManager;
@end

And the .main file:

#import "ViewController.h"
#import "MapViewAnnotation.h"
@interface ViewController () @end
@implementation ViewController
@synthesize mapView, locationManager;
- (void)viewDidLoad{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    self.mapView.delegate = self;

    self.locationManager = [[CLLocationManager alloc] init];
    [locationManager setDelegate:self];

    [locationManager setDistanceFilter:kCLDistanceFilterNone];
    [locationManager setDesiredAccuracy:kCLLocationAccuracyBest];

    [self.mapView setShowsUserLocation:YES];

    CLLocationCoordinate2D location;
    location.latitude = 37.78608;
    location.longitude = -122.405398;

    MapViewAnnotation *mapAnnotation = [[MapViewAnnotation alloc] initWithTitle:@"Store location" coordinate:location];
    [self.mapView addAnnotation:mapAnnotation];
}
-(void) mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)views{
    MKAnnotationView *annotationView = [views objectAtIndex:0];
    id<MKAnnotation> mp = [annotationView annotation];

    MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance([mp coordinate], 250, 250);
    [self.mapView setRegion:region animated:YES];
}
@end

It displays my current location successfully, but when I use this line in viewDidLoad:

MapViewAnnotation *mapAnnotation = [[MapViewAnnotation alloc] initWithTitle:@"Store location" coordinate:location];

I get this exception:

MapKitDemo[3426:c07] -[MapViewAnnotation setCoordinate:]: unrecognized selector sent to instance 0x8551ae0
2012-10-03 16:19:23.070 MapKitDemo[3426:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MapViewAnnotation setCoordinate:]: unrecognized selector sent to instance 0x8551ae0'

What am I doing wrong?

Answer 1

You are using the property self.coordinate in the -initWithTitle:coordinate: method of your subclass, this means that the coordinate is being set using the property as opposed to the iVar, since this property is set to readonly , you are getting this error and probably crash...

You must access the iVar directly like so:

#import "MapViewAnnotation.h"
@implementation MapViewAnnotation

@synthesize title = _title, coordinate = _coordinate    

- (id) initWithTitle:(NSString *) t coordinate:(CLLocationCoordinate2D) c{
    self = [super init];
    if(self){
        _title = t;
        _coordinate = c;
        // self.coordinate = c /* !This is readonly ! */
    }
    return self;
}
@end

Notice I also changed the @synthesize (which isn't required anymore - this is done automatically as of Xcode 4.5 I believe? Maybe an earlier version). Also note that I did a condition in your init, you should do this it will make sure you don't try to et properties/iVars on nil in the case that [super init] failed to initialise your object.

Answer 2

coordinate is a readonly property. You can't use the setter for it. Use the ivar or make it read/write.