即使您滚动，地图视图的中心也有地标/注释

Question

我花了很多时间试图弄清楚如何做到这一点：

在中心坐标中有一个地标/注释在您的地图视图中，当您滚动地图时，地标应始终位于中心。

我见过另一个应用程序也这样做！

Answer 1

在如何在中心添加注释中找到了我的问题iPhone 中的地图视图？

答案是：

如果您想使用实际的注释而不仅仅是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（预定义的MKPointAnnotation 类（例如）。这避免了当中心发生变化时必须删除和添加注释。
• 在 viewDidLoad 中创建注释
• ，在属性中保留对其的引用，例如 centerAnnotation
• 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）

在 ：

@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。如果您需要注释移动得更流畅，可以将 UIPanGestureRecognizer 和 UIPinchGestureRecognizer 添加到地图视图，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;
}