StackOverflow2013

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copied!<p>If you want to use an actual annotation instead of just a regular view positioned above the center of the map view, you can:</p> <ul> <li>use an annotation class with a settable coordinate property (pre-defined <code>MKPointAnnotation</code> class eg). This avoids having to remove and add the annotation when the center changes.</li> <li>create the annotation in viewDidLoad</li> <li>keep a reference to it in a property, say centerAnnotation</li> <li>update its coordinate (and title, etc) in the map view's <code>regionDidChangeAnimated</code> delegate method (make sure map view's delegate property is set)</li> </ul> <p>Example:</p> <pre><code>@interface SomeViewController : UIViewController <MKMapViewDelegate> { MKPointAnnotation *centerAnnotation; } @property (nonatomic, retain) MKPointAnnotation *centerAnnotation; @end @implementation SomeViewController @synthesize centerAnnotation; - (void)viewDidLoad { [super viewDidLoad]; MKPointAnnotation *pa = [[MKPointAnnotation alloc] init]; pa.coordinate = mapView.centerCoordinate; pa.title = @"Map Center"; pa.subtitle = [NSString stringWithFormat:@"%f, %f", pa.coordinate.latitude, pa.coordinate.longitude]; [mapView addAnnotation:pa]; self.centerAnnotation = pa; [pa release]; } - (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated { centerAnnotation.coordinate = mapView.centerCoordinate; centerAnnotation.subtitle = [NSString stringWithFormat:@"%f, %f", centerAnnotation.coordinate.latitude, centerAnnotation.coordinate.longitude]; } - (void)dealloc { [centerAnnotation release]; [super dealloc]; } @end </code></pre> <p>Now this will move the annotation but not smoothly. If you need the annotation to move more smoothly, you can add a <code>UIPanGestureRecognizer</code> and <code>UIPinchGestureRecognizer</code> to the map view and also update the annotation in the gesture handler:</p> <pre><code> // (Also add UIGestureRecognizerDelegate to the interface.) // In viewDidLoad: UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleGesture:)]; panGesture.delegate = self; [mapView addGestureRecognizer:panGesture]; [panGesture release]; UIPinchGestureRecognizer *pinchGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(handleGesture:)]; pinchGesture.delegate = self; [mapView addGestureRecognizer:pinchGesture]; [pinchGesture release]; - (void)handleGesture:(UIGestureRecognizer *)gestureRecognizer { centerAnnotation.coordinate = mapView.centerCoordinate; centerAnnotation.subtitle = [NSString stringWithFormat:@"%f, %f", centerAnnotation.coordinate.latitude, centerAnnotation.coordinate.longitude]; } - (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer { //let the map view's and our gesture recognizers work at the same time... return YES; } </code></pre>

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