MKAnnotationView update title and subtitle with distance when event is received

Question

Hello,

I'm developing an iphone app using mapkit and CLLocationManager.

I put lots of MKPinAnnotationView on map (about 100) and I want to update all callout's subtitle whith user distance when I receive it.

How to do it ?

Thanks, David

Answer 1

It depends on how you are creating your MKAnnotations.

You should probably have an object like "Place" represented by Place.h and Place.m, which conform to the MKAnnotation protocol...

Place would have a property along the lines of

float distance;

Then your subtitle method (part of MKAnnotation) would do something like this

- (NSString *)subtitle
{
    return [NSString stringWithFormat:@"%0.2f Miles Away", distance];
}

That subtitle method gets called by the mapview constantly (in fact its almost ridiculous how often it gets called), so as soon as you manipulate the value of distance, it will be reflected on the map (perhaps as early as the next time you tap on the pin).

Answer 2

I try this to update subtitle callout with new location but it didn't work well.

In my MyAppDelegate.h

extern NSString * const GMAP_USERLOCATION_CHANGED; 

@interface MyAppDelegate : NSObject <UIApplicationDelegate> {
    CLLocationManager *locationManager;
    CLLocation *userLocation;
}
@property (nonatomic, retain) CLLocationManager *locationManager;
@property (nonatomic, retain) CLLocation *userLocation;
@end

In my MyAppDelegate.m

@implementation MyAppDelegate

NSString * const GMAP_USERLOCATION_CHANGED = @"gMapUserLocationChanged"; 
@synthesize locationManager, userLocation;

- (void)applicationDidFinishLaunching:(UIApplication *)application
{    
    userLocation = nil;
    [[self locationManager] startUpdatingLocation];

    [window addSubview:tabBarController.view];
    [window makeKeyAndVisible];
}

#pragma mark -
#pragma mark Core Location delegate
- (CLLocationManager *)locationManager 
{
    if (locationManager != nil) 
 {
        return locationManager;
    }

    locationManager = [[CLLocationManager alloc] init];
    locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters;
    locationManager.delegate = self;

    return locationManager; 
}

- (void)locationManager:(CLLocationManager *)manager
     didUpdateToLocation:(CLLocation *)newLocation
                   fromLocation:(CLLocation *)oldLocation 
{
 self.userLocation = newLocation;
 // send notification to defaulcenter
 NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
 [nc postNotificationName:GMAP_USERLOCATION_CHANGED object:self.userLocation];
}


- (void)dealloc {
    [window release];
    [locationManager release];
    [userLocation release];

    [super dealloc];
}

@end

I made a customAnnotationView named MyAnnotation.

in MyAnnotation.h :

@interface MyAnnotation : MKPinAnnotationView<MKAnnotation>
{
 double longitude;
 double latitude;
 NSString *title;
 NSString *subtitle;

}

@property (nonatomic, retain) NSString *title;
@property (nonatomic, retain) NSString *subtitle;
@property double longitude;
@property double latitude;
@end

in MyAnnotation.m :

#import "MyAnnotation.h"
#import "MyAppDelegate.h"

@implementation MyAnnotation

@synthesize title, subtitle;
@synthesize longitude;
@synthesize latitude;

-(id)initWithAnnotation:(id <MKAnnotation>)annotation reuseIdentifier:(NSString *)reuseIdentifier
{
 self = [super initWithAnnotation:annotation reuseIdentifier:reuseIdentifier];
 if (self != nil) 
 {
  NSLog(@"add observer");
  NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
  [nc addObserver:self selector:@selector(receivedNewUserLocation:) name:GMAP_USERLOCATION_CHANGED object:nil];
 }
 return self;
}

- (void)setTitleAndSubtitle 
{
 [self setTitleAndSubtitle:nil];
}

- (id)setTitleAndSubtitle:(CLLocation*)userLocation
{
 CLLocationDistance dist = -1;

 if(userLocation)
 {
  CLLocation *poiLoc = [[CLLocation alloc] initWithLatitude:self.latitude longitude:self.longitude];
  dist = [userLocation distanceFromLocation:poiLoc] / 1000;
  NSLog(@"distance is now %.f", dist);
 }

 title = @"the Title of the poi!";

 subtitle = [NSString stringWithFormat:@"Distance: %@", 
    dist > -1 ? [NSString stringWithFormat:@"%.2f km", dist] : @"-"
    ];

 return self;
}

- (void)receivedNewUserLocation:(NSNotification *)userLocationNotification
{
 CLLocation *userlocation = (CLLocation*)[userLocationNotification object];
 [self setTitleAndSubtitle:userlocation];
}

- (CLLocationCoordinate2D)coordinate;
{
    CLLocationCoordinate2D theCoordinate;
    theCoordinate.latitude = latitude;
    theCoordinate.longitude = longitude;
    return theCoordinate; 
}

- (NSString *)title
{
    return title;
}

- (NSString *)subtitle
{
    return subtitle;
}

- (void)dealloc
{ 
    [title release];
    [subtitle release];

    NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
    [nc removeObserver:self];

    [super dealloc];
}
@end

In the end I use it like that in my MapViewController (I put only the viewForAnnotation delegate method here):

- (MKAnnotationView *)mapView:(MKMapView *)theMapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    // if it's the user location, just return nil.
    if ([annotation isKindOfClass:[MKUserLocation class]])
        return nil;

    MyAnnotation *annotationView = nil;
    MyAnnotation* myAnnotation = (MyAnnotation *)annotation;
    // try to dequeue an existing pin view first
    NSString* identifier = @"CustomMapAnnotation";
    MyAnnotation *customPinView = (MyAnnotation *)[self.mapView dequeueReusableAnnotationViewWithIdentifier:identifier];


    if(nil == customPinView) 
    {
 // if an existing pin view was not available, create one
 customPinView = [[[MyAnnotation alloc]
    initWithAnnotation:myAnnotation 
    reuseIdentifier:identifier] 
    autorelease];

 customPinView.animatesDrop = YES;
 customPinView.canShowCallout = YES;
    }

    annotationView = customPinView;
    [annotationView setEnabled:YES];
    [annotationView setCanShowCallout:YES];

    return annotationView;
}

After all of this subtitle is not update after the mkannotation is load on map.... What's wrong ?

thanks for your help...