Drag an annotation pin on a mapview

Question

The annotation pin is draggable but I couldn't drop it to the destination location. The problem is how could I get the destination location's coordinate where i drop the annotation pin? Any method exist?

Edit 1:

The center of the annotation pin seems never changed where ever I drop the pin.

- (void)mapView:(MKMapView *)mapView annotationView:(MKAnnotationView *)annotationView didChangeDragState:(MKAnnotationViewDragState)newState 
fromOldState:(MKAnnotationViewDragState)oldState 
{
if (newState == MKAnnotationViewDragStateEnding)
{
    NSLog(@"x is %f", annotationView.center.x);
    NSLog(@"y is %f", annotationView.center.y);

    CGPoint dropPoint = CGPointMake(annotationView.center.x, annotationView.center.y);
    CLLocationCoordinate2D newCoordinate = [self.mapView convertPoint:dropPoint toCoordinateFromView:annotationView.superview];
    [annotationView.annotation setCoordinate:newCoordinate];

}
}

Edit 2:

Annotation.h

@property (nonatomic,readwrite,assign) CLLocationCoordinate2D coordinate;

Annotation.m

- (void)setCoordinate:(CLLocationCoordinate2D)newCoordinate {
coordinate = newCoordinate; 
}

Edit 3: where ever I drag the pin, the NSLog out put of the droppedAt is always the same.

- (void)mapView:(MKMapView *)mapView annotationView:(MKAnnotationView *)annotationView didChangeDragState:(MKAnnotationViewDragState)newState 
fromOldState:(MKAnnotationViewDragState)oldState 
{
if (newState == MKAnnotationViewDragStateEnding)
{
    CLLocationCoordinate2D droppedAt = annotationView.annotation.coordinate;
    NSLog(@"Pin dropped at %f,%f", droppedAt.latitude, droppedAt.longitude);
}
}

Edit 4:

Annotaion.m @dynamic startAddr;

- (CLLocationCoordinate2D)coordinate
{
coordinate.latitude = [self.startAddr.latitude doubleValue];
coordinate.longitude = [self.startAddr.longitude doubleValue];    
return coordinate;
}

- (void)setCoordinate:(CLLocationCoordinate2D)newCoordinate {
//I need to update the self.startAddr.latitude and longitude here. Problem solved.
self.startAddr.latitude = [NSNumber numberWithDouble:newCoordinate.latitude];
self.startAddr.longitude = [NSNumber numberWithDouble:newCoordinate.longitude];

coordinate = newCoordinate; 
}

Answer 1

First you have to create a custom annotation like this:

MyAnnotation.h

#import <MapKit/MapKit.h>

@interface MyAnnotation : NSObject <MKAnnotation>{

    CLLocationCoordinate2D coordinate;

}
- (id)initWithCoordinate:(CLLocationCoordinate2D)coord;
- (void)setCoordinate:(CLLocationCoordinate2D)newCoordinate;
@end

MyAnnotation.m

#import "MyAnnotation.h"

@implementation MyAnnotation
@synthesize coordinate;

- (NSString *)subtitle{
    return nil;
}

- (NSString *)title{
    return nil;
}

-(id)initWithCoordinate:(CLLocationCoordinate2D)coord {
    coordinate=coord;
    return self;
}

-(CLLocationCoordinate2D)coord
{
    return coordinate;
}

- (void)setCoordinate:(CLLocationCoordinate2D)newCoordinate {
    coordinate = newCoordinate; 
}

@end

After that, you just have to use your annotation like this:

// Assuming you have imported MyAnnotation.h and you have a self.map property pointing to a MKMapView
MyAnnotation *myPin = [[MyAnnotation alloc] initWithCoordinate:self.map.centerCoordinate]; // Or whatever coordinates...
[self.map addAnnotation:myPin];

Also, you have to return a view for your annotation. You can do so like this:

- (MKAnnotationView *) mapView: (MKMapView *) mapView viewForAnnotation: (id<MKAnnotation>) annotation {
    MKPinAnnotationView *pin = (MKPinAnnotationView *) [self.map dequeueReusableAnnotationViewWithIdentifier: @"myPin"];
    if (pin == nil) {
        pin = [[[MKPinAnnotationView alloc] initWithAnnotation: annotation reuseIdentifier: @"myPin"] autorelease]; // If you use ARC, take out 'autorelease'
    } else {
        pin.annotation = annotation;
    }
    pin.animatesDrop = YES;
    pin.draggable = YES;

    return pin;
}

Then, once you have adopted the MKMapViewDelegate protocol in your controller, you grab the coordinates of a pin after dragging it like this:

- (void)mapView:(MKMapView *)mapView 
 annotationView:(MKAnnotationView *)annotationView 
didChangeDragState:(MKAnnotationViewDragState)newState 
   fromOldState:(MKAnnotationViewDragState)oldState 
{
    if (newState == MKAnnotationViewDragStateEnding)
    {
        CLLocationCoordinate2D droppedAt = annotationView.annotation.coordinate;
        NSLog(@"Pin dropped at %f,%f", droppedAt.latitude, droppedAt.longitude);
    }
}