I have MAP view in my app and i want to add Annotation pin (Red pin) on center of map view.

Now when user scroll map view pin should adjust with cent开发者_如何学运维er according to that.

How to do that?

Thank

If you want to use an actual annotation instead of just a regular view positioned above the center of the map view, you can:

• use an annotation class with a settable coordinate property (pre-defined MKPointAnnotation class eg). This avoids having to remove and add the annotation when the center changes.
• create the annotation in viewDidLoad
• keep a reference to it in a property, say centerAnnotation
• update its coordinate (and title, etc) in the map view's regionDidChangeAnimated delegate method (make sure map view's delegate property is set)

Example:

@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

Now this will move the annotation but not smoothly. If you need the annotation to move more smoothly, you can add a UIPanGestureRecognizer and UIPinchGestureRecognizer to the map view and also update the annotation in the gesture handler:

    // (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;
}

Anna's answer is clever approach to keeping an annotation centered in the map using the annotations in the standard mapview way. However, as one commenter pointed out, the scrolling and pinching while much better still shows noticeable lag, and the recommended approach would be to add the annotation view as a subview of the mapview. Here's what that looks like.

@interface SHCenterPinMapViewController () <MKMapViewDelegate>

@property (weak, nonatomic) IBOutlet MKMapView *mapView;
@property (strong, nonatomic) MKPointAnnotation *centerAnnotaion;
@property (strong, nonatomic) MKPinAnnotationView *centerAnnotationView;

@end

@implementation SHCenterPinMapViewController

- (MKPointAnnotation *)centerAnnotaion
{
    if (!_centerAnnotaion) {
        _centerAnnotaion = [[MKPointAnnotation alloc] init];
    }

    return _centerAnnotaion;
}

- (MKPinAnnotationView *)centerAnnotationView
{
    if (!_centerAnnotationView) {
        _centerAnnotationView = [[MKPinAnnotationView alloc] initWithAnnotation:self.centerAnnotaion
                                                                reuseIdentifier:@"centerAnnotationView"];
    }

    return _centerAnnotationView;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.mapView.delegate = self;
    [self.mapView addSubview:self.centerAnnotationView];
}

-(void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    [self moveMapAnnotationToCoordinate:self.mapView.centerCoordinate];
}

// These are the constants need to offset distance between the lower left corner of
// the annotaion view and the head of the pin
#define PIN_WIDTH_OFFSET 7.75
#define PIN_HEIGHT_OFFSET 5

- (void)moveMapAnnotationToCoordinate:(CLLocationCoordinate2D) coordinate
{
    CGPoint mapViewPoint = [self.mapView convertCoordinate:coordinate toPointToView:self.mapView];

    // Offset the view from to account for distance from the lower left corner to the pin head
    CGFloat xoffset = CGRectGetMidX(self.centerAnnotationView.bounds) - PIN_WIDTH_OFFSET;
    CGFloat yoffset = -CGRectGetMidY(self.centerAnnotationView.bounds) + PIN_HEIGHT_OFFSET;

    self.centerAnnotationView.center = CGPointMake(mapViewPoint.x + xoffset,
                                                   mapViewPoint.y + yoffset);
}

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated
{
    self.centerAnnotaion.coordinate = mapView.centerCoordinate;
    [self moveMapAnnotationToCoordinate:mapView.centerCoordinate];
}

@end

Really the only interesting thing to not is that you have to offset the MKPinAnnotationView by a certain amount to account for the distance between the lower left corner and the pin head. I don't like having these asset dependent constants in the code, so if anyone can find a better way to do that, I am all ears.

I created a github project with a map controller that does this as well as some other things related to using a mapview to have a user select a location. Check it out here: https://github.com/scottrhoyt/CenterPinMapViewController

Swift version

In class:

var centerAnnotation = MKPointAnnotation()
var centerAnnotationView = MKPinAnnotationView()

In viewDidLoad:

if #available(iOS 9.0, *) {
        centerAnnotationView.pinTintColor = customColor
    } else {
        // Fallback on earlier versions
        centerAnnotationView.pinColor = MKPinAnnotationColor.Red
    }
self.view.addSubview(centerAnnotationView)

In viewDidAppear:

self.moveMapAnnotationToCoordinate(self.mapView.centerCoordinate)

Then:

func moveMapAnnotationToCoordinate(locate : CLLocationCoordinate2D ) {
    let mapViewPoint : CGPoint = self.mapView.convertCoordinate(locate, toPointToView: self.mapView)
    let pinWidth : CGFloat = 7.75
    let pinHeight : CGFloat = 7
    let xOffset : CGFloat = CGRectGetMidX(self.centerAnnotationView.bounds) - pinWidth
    let yOffset : CGFloat = CGRectGetMidY(self.centerAnnotationView.bounds) - pinHeight

    self.centerAnnotationView.center = CGPointMake(mapViewPoint.x - xOffset, mapViewPoint.y - yOffset)
}

For using change in location, add delegate CLLocationManagerDelegate and then:

func mapView(mapView: MKMapView, regionDidChangeAnimated animated: Bool) {
    self.centerAnnotation.coordinate = self.mapView.centerCoordinate
    self.moveMapAnnotationToCoordinate(self.mapView.centerCoordinate)
}