如何在iPhone中的地图视图中心添加注释？

Question

我在我的应用程序中有MAP视图,我想在地图视图的中心添加注释引脚(红色图钉).
现在当用户滚动地图视图引脚应根据该中心进行调整.
怎么做？
谢谢

Answer 1

如果要使用实际注释而不是仅位于地图视图中心上方的常规视图,您可以:

• 使用具有可设置坐标属性的注释类(MKPointAnnotation例如,预定义类).这样可以避免在中心更改时删除和添加注释.
• 在viewDidLoad中创建注释
• 在一个属性中保留对它的引用,比如centerAnnotation
• 在地图视图的regionDidChangeAnimated委托方法中更新其坐标(和标题等)(确保设置了地图视图的委托属性)

例:

@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

现在这将移动注释但不顺利.如果需要注释更平滑地移动,可以在地图视图中添加一个UIPanGestureRecognizer和UIPinchGestureRecognizer更新注释,并在手势处理程序中更新注释:

    // (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;
}

Answer 2

安娜的答案是一种聪明的方法，即使用标准的mapview方式中的注释将注释保持在地图中心。但是，正如一位评论者所指出的那样，滚动和收缩虽然更好，但仍然显示出明显的滞后，建议的方法是将注释视图添加为mapview的子视图。看起来像这样。

@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

真的唯一有趣的事情是，您必须将MKPinAnnotationView偏移一定的量，以说明左下角和针头之间的距离。我不喜欢在代码中包含这些依赖于资产的常量，因此，如果有人可以找到更好的方法来做到这一点，我将不知所措。

我创建了一个带有地图控制器的github项目，它执行此操作以及与使用mapview让用户选择位置有关的其他一些操作。在这里查看：https : //github.com/scottrhoyt/CenterPinMapViewController