Marking a location in a MKMapView

Question

I'm trying to mark a location in a map view.

First I implemented the MKAnnotation protocol in a separate class like this.

AddressAnnotation.h

#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>

@interface AddressAnnotation : NSObject <MKAnnotation>

@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;

- (id)initWithCoordinates:(CLLocationCoordinate2D)location;

@end

AddressAnnotation.m

#import "AddressAnnotation.h"

@implementation AddressAnnotation

- (id)initWithCoordinates:(CLLocationCoordinate2D)location
{
    self = [super init];
    if (self)
    {
        self.coordinate = location;
    }

    return self;
}

@end

Then in the view controller, I implemented the MKMapViewDelegate.

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    if ([annotation isKindOfClass:[MKUserLocation class]])
    {
        return nil;
    }

    static NSString *myIdentifier = @"myIndentifier";
    MKPinAnnotationView *pinView = (MKPinAnnotationView *)[mapView dequeueReusableAnnotationViewWithIdentifier:myIdentifier];

    if (!pinView)
    {
        pinView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:myIdentifier];
        pinView.pinColor = MKPinAnnotationColorRed;
        pinView.animatesDrop = NO;
    }
    return pinView;
}

And in the viewDidLoad method, I initialize an instance of the AddressAnnotation class.

- (void)viewDidLoad
{
    [super viewDidLoad];

    CLLocationCoordinate2D coordinate = CLLocationCoordinate2DMake(34.421496, -119.70182);

    AddressAnnotation *pinAnnotation = [[AddressAnnotation alloc] initWithCoordinates:coordinate];
    [self.mapView addAnnotation:pinAnnotation];
}

I keep getting the following error though.

-[AddressAnnotation setCoordinate:]: unrecognized selector sent to instance

I'm not sure what I'm doing wrong here. Can someone please help me out?

Thank you.

score 1 · Accepted Answer · answered Jan 25 '14 at 15:38

1

The problem is that you defined a readonly coordinate property. Therefore you get an exception when trying to set it. Just remove your coordinate property definition, as this is already provided by the MKAnnotation protocol.

answered Jan 25 '14 at 15:38

rist

578
2
9

I got it working. Thanks. But the region shown in the screen isn't the marked area. How do I focus on the region where the pin is when the app starts? – Isuru Jan 25 '14 at 15:55
MKCoordinateRegion mapRegion; mapRegion.center = coordinate; mapRegion.span.latitudeDelta = 0.05; mapRegion.span.longitudeDelta = 0.05; [mapView setRegion:region animated:YES] – Zeb Jan 25 '14 at 16:17

Gianluca Tranchedone · Answer 2 · 2014-01-25T15:43:35.323

0

Your problem is that the coordinate property is readonly. Moreover, it's already defined by the MKAnnotation protocol.

When you implement a protocol defines @properties you actually have to @syntentize those properties to create a backing instance variable (ivar) in your class or, alternatively, you got to implement custom setter and getter for those properties.

Remember: a property is nothing more that a setter and getter method and can be optionally backed by an ivar. Being backed by an ivar is a @property's default behaviour.

So, in short, to fix your problem in your AddressAnnotation.h file delete the coordinate property and in the AddressAnnotion.m file add:

// after the line @implementation Address Annotation
@syntetize coordinate = _coordinate;

edited Jan 25 '14 at 15:43

answered Jan 25 '14 at 15:36

Gianluca Tranchedone

3,598
1
18
33

I don't know why you got downvoted but you're right. That was the problem. Thanks, I managed to correct it. :) I had to accept rist's answer because he posted it here first but thanks for the detailed answer. – Isuru Jan 25 '14 at 15:54
there is no need to synthesize properties any more – rist Jan 26 '14 at 12:11
There is if the property is defined in a protocol. In fact you'll get a warning from Xcode if you don't do so. – Gianluca Tranchedone Jan 26 '14 at 12:28

Marking a location in a MKMapView

2 Answers2