Search code examples
iphonemapkitmkannotation

Setting map view annotation properties

I am working on display a map with annotation on it. What I have so far is

Annotation.h

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

@interface Annotation : NSObject <MKAnnotation> 

@end

MapViewController.m 

Annotation *pin = [[Annotation alloc] init];    
[pin title]       = storeName;   
[pin subtitle]    = storeAddress;   
[pin coordinate]  = region.center;       
[mapView addAnnotation:pin];

However, I got an error like below:

expression is not assignable for title, subtitle and coordinate

Does anyone have any idea about this issue?

Solution

  • First, these lines try to assign a value to a method call which is what the error is saying you can't do:

    [pin title]       = storeName;   
[pin subtitle]    = storeAddress;   
[pin coordinate]  = region.center;

    They should be like this:

    pin.title       = storeName;   
pin.subtitle    = storeAddress;   
pin.coordinate  = region.center;


    However, the MKAnnotation protocol defines the properties as readonly. To be able to set them, declare them in your Annotation class as:

    @property (nonatomic, assign) CLLocationCoordinate2D coordinate;
@property (nonatomic, copy) NSString *title;
@property (nonatomic, copy) NSString *subtitle;

    and add the @synthesize lines for them in Annotation.m.


    However, if all you need are the title, subtitle, and coordinate properties, you don't need to create your own class to implement MKAnnotation. Instead, just use the built-in MKPointAnnotation class which already implements those properties as settable:

    MKPointAnnotation *pin = [[MKPointAnnotation alloc] init];


    Another option, as @macbirdie points out, is just to make your existing Store class (if you have one) implement the MKAnnotation protocol.