Moving annotations in MKMapView according to server data (latitude and longitude)

Question

In my app I am showing location of some other person by getting their location (latitude and longitude) from server at particular interval.

After getting I have to remove all annotations and drop new annotations based on the server data.

But it looks very inefficient as when we have the annotation for the same user previously exists even then I'm removing and adding the same user annotation.

So I want to know can we move the MKAnnotation from one coordinate to other? I have tried "setCoordinate" property but unable to succesfuly implement it.

Also it is not "touch and drag" kind. The annotations move itself when the app get data (latitude and longitude) from server.

Answer 1

Why is that a performance problem? Have you mesaured it? You're just changing an array of objects, not even creating new instances.

The AnnotationViews on the MapView will be reused anyway. There shouldn't be any problems with that.

Answer 2

To change an annotation's coordinate without removing, re-creating and adding it again, create an annotation class where the coordinate property is settable. A simple way to do this is to define the coordinate property like this:

@property (nonatomic, assign) CLLocationCoordinate2D coordinate;

Alternatively, instead of defining your own class, you could also use the built-in MKPointAnnotation class which has a settable coordinate.

You initially create and add the annotations as usual. For example:

MKPointAnnotation *pa = [[MKPointAnnotation alloc] init];
pa.coordinate = someCoordinate;
pa.title = @"User1";
[mapView addAnnotation:pa];
[pa release];

Later, when you get an update from the server and the coordinates for "User1" change, you can either search for that user's annotation in the map view's annotations array or store the references to the annotations in some other structure that allows quick access using a key like an NSMutableDictionary.

Once you have found the annotation, you just set the annotation's coordinate property to the new value and the map view will automatically move the annotation's view to the new location.

This example searches the annotations array:

for (id<MKAnnotation> ann in mapView.annotations)
{
    if ([ann.title isEqualToString:@"User1"])
    {
        ann.coordinate = theNewCoordinate;
        break;
    }
}

If you want to find the annotation using a different, custom property of your annotation class (say some int named userIdNumber):

for (id<MKAnnotation> ann in mapView.annotations)
{
    if ([ann isKindOfClass:[YourAnnotationClass class]])
    {
        YourAnnotationClass *yacAnn = (YourAnnotationClass *)ann;
        if (yacAnn.userIdNumber == user1Id)
        {
            yacAnn.coordinate = theNewCoordinate;
            break;
        }
    }
}

The above is just an example of how to change the coordinate. If you have lots of annotations with changing coordinates, I don't recommend searching for them one-at-a-time. Instead, you could store the references in a dictionary and look them up quickly using a key value.