Mapkit +closest annotation

Question

Hi all,

I am trying to devellopp an app showing the nearest poi to the users location.

My app is now capable of: showing a map (Mapkit) with 110 annotations and the user's location.

Furthermore, I have a TableView at the bottom of my screen, to choose between the different annotations. However, they're listed by number, and not by proximity to the user's location, which is my wish.

My research have led me to think that I should use CLLocation for getting the user's location. I then have really no idea on how to do it next, using getDistancefrom.

My annotations are stored on SecondViewController.m, using this form:

-(void)loadOurAnnotations
{
    CLLocationCoordinate2D workingCoordinate;

    workingCoordinate.latitude = XX.XXXXX;
    workingCoordinate.longitude = XX.XXXXX;
    SecondViewAnnotation *POI1 = [[SecondViewAnnotation alloc] initWithCoordinate:workingCoordinate];
    [POI1 setTitle:@"POI"];
    [POI1 setSubtitle:@"StreetName"];
    [POI1 setAnnotationType:SecondViewAnnotationTypePOI1];

    [mapView addAnnotation:POI1]; 
    ...

and so on to POI110.

Could someone please give me a clue? I'm a total newbie!

Thank you in advance for your help,

Answer 1

NSArray class provide several methods for sorting its contents. For example you can sort your annotations using sortedArrayUsingFunction:context:. To do that you need to implement a function that compares 2 arbitrary elements (here we will also use current user location passed to the function via context parameter):

NSInteger distanceSort(id annot1, id annot2, void *context){
    SecondViewAnnotation* poi1 = (SecondViewAnnotation*)annot1;
    SecondViewAnnotation* poi2 = (SecondViewAnnotation*)annot2;
    CLLocation* userLocation = (CLLocation*)context;
    CLLocation* location1 = [[CLLocation alloc] initWithLatitude:poi1.coordinate.latitude,
                      longitude:poi1.coordinate.longitude];
    CLLocation* location2 = [[CLLocation alloc] initWithLatitude:poi2.coordinate.latitude,
                      longitude:poi2.coordinate.longitude];

    CLLocationDistance distance1 = [userLocation getDistanceFrom:location1];
    CLLocationDistance distance2 = [userLocation getDistanceFrom:location2];
    [location1 release];
    [location2 release];

    if (distance1 > distance2)
       return NSOrderedDescending;

    if (distance1 < distance2)
       return NSOrderedAscending;

    return NSOrderedSame;       
}

Then somewhere in your code you can do the following:

if (mapView.userLocation.location)
    //Do not forget to release `sortedArray` when you do not need it to avoid memory leak.
    sortedArray = [[mapView.annotations sortedArrayUsingFunction:distanceSort context:mapView.userLocation.location] retain];

Answer 2

hi Vladmir can u put more comments i want know how does it work plizzz i'm total newbie too. thanks