MKAnnotationView 在收到事件时更新标题和副标题与距离

Question

我正在使用 mapkit 和 CLLocationManager 开发一个 iphone 应用程序。

我在地图上放了很多 MKPinAnnotationView（大约 100 个），我想在收到它时更新所有标注的字幕与用户距离。

怎么做？

谢谢

---

我尝试使用新位置更新字幕标注，但效果不佳。

在我的 MyAppDelegate.h 中

extern NSString * const GMAP_USERLOCATION_CHANGED; 

@interface MyAppDelegate : NSObject <UIApplicationDelegate> {
    CLLocationManager *locationManager;
    CLLocation *userLocation;
}
@property (nonatomic, retain) CLLocationManager *locationManager;
@property (nonatomic, retain) CLLocation *userLocation;
@end

在我的 MyAppDelegate.m 中

@implementation MyAppDelegate

NSString * const GMAP_USERLOCATION_CHANGED = @"gMapUserLocationChanged"; 
@synthesize locationManager, userLocation;

- (void)applicationDidFinishLaunching:(UIApplication *)application
{    
    userLocation = nil;
    [[self locationManager] startUpdatingLocation];

    [window addSubview:tabBarController.view];
    [window makeKeyAndVisible];
}

#pragma mark -
#pragma mark Core Location delegate
- (CLLocationManager *)locationManager 
{
    if (locationManager != nil) 
 {
        return locationManager;
    }

    locationManager = [[CLLocationManager alloc] init];
    locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters;
    locationManager.delegate = self;

    return locationManager; 
}

- (void)locationManager:(CLLocationManager *)manager
     didUpdateToLocation:(CLLocation *)newLocation
                   fromLocation:(CLLocation *)oldLocation 
{
 self.userLocation = newLocation;
 // send notification to defaulcenter
 NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
 [nc postNotificationName:GMAP_USERLOCATION_CHANGED object:self.userLocation];
}


- (void)dealloc {
    [window release];
    [locationManager release];
    [userLocation release];

    [super dealloc];
}

@end

我创建了一个名为 MyAnnotation 的 customAnnotationView。

在 MyAnnotation.h 中：

@interface MyAnnotation : MKPinAnnotationView<MKAnnotation>
{
 double longitude;
 double latitude;
 NSString *title;
 NSString *subtitle;

}

@property (nonatomic, retain) NSString *title;
@property (nonatomic, retain) NSString *subtitle;
@property double longitude;
@property double latitude;
@end

在 MyAnnotation.m 中：

#import "MyAnnotation.h"
#import "MyAppDelegate.h"

@implementation MyAnnotation

@synthesize title, subtitle;
@synthesize longitude;
@synthesize latitude;

-(id)initWithAnnotation:(id <MKAnnotation>)annotation reuseIdentifier:(NSString *)reuseIdentifier
{
 self = [super initWithAnnotation:annotation reuseIdentifier:reuseIdentifier];
 if (self != nil) 
 {
  NSLog(@"add observer");
  NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
  [nc addObserver:self selector:@selector(receivedNewUserLocation:) name:GMAP_USERLOCATION_CHANGED object:nil];
 }
 return self;
}

- (void)setTitleAndSubtitle 
{
 [self setTitleAndSubtitle:nil];
}

- (id)setTitleAndSubtitle:(CLLocation*)userLocation
{
 CLLocationDistance dist = -1;

 if(userLocation)
 {
  CLLocation *poiLoc = [[CLLocation alloc] initWithLatitude:self.latitude longitude:self.longitude];
  dist = [userLocation distanceFromLocation:poiLoc] / 1000;
  NSLog(@"distance is now %.f", dist);
 }

 title = @"the Title of the poi!";

 subtitle = [NSString stringWithFormat:@"Distance: %@", 
    dist > -1 ? [NSString stringWithFormat:@"%.2f km", dist] : @"-"
    ];

 return self;
}

- (void)receivedNewUserLocation:(NSNotification *)userLocationNotification
{
 CLLocation *userlocation = (CLLocation*)[userLocationNotification object];
 [self setTitleAndSubtitle:userlocation];
}

- (CLLocationCoordinate2D)coordinate;
{
    CLLocationCoordinate2D theCoordinate;
    theCoordinate.latitude = latitude;
    theCoordinate.longitude = longitude;
    return theCoordinate; 
}

- (NSString *)title
{
    return title;
}

- (NSString *)subtitle
{
    return subtitle;
}

- (void)dealloc
{ 
    [title release];
    [subtitle release];

    NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
    [nc removeObserver:self];

    [super dealloc];
}
@end

最后我在我的 MapViewController 中使用它（我在这里只放了 viewForAnnotation 委托方法）：

- (MKAnnotationView *)mapView:(MKMapView *)theMapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    // if it's the user location, just return nil.
    if ([annotation isKindOfClass:[MKUserLocation class]])
        return nil;

    MyAnnotation *annotationView = nil;
    MyAnnotation* myAnnotation = (MyAnnotation *)annotation;
    // try to dequeue an existing pin view first
    NSString* identifier = @"CustomMapAnnotation";
    MyAnnotation *customPinView = (MyAnnotation *)[self.mapView dequeueReusableAnnotationViewWithIdentifier:identifier];


    if(nil == customPinView) 
    {
 // if an existing pin view was not available, create one
 customPinView = [[[MyAnnotation alloc]
    initWithAnnotation:myAnnotation 
    reuseIdentifier:identifier] 
    autorelease];

 customPinView.animatesDrop = YES;
 customPinView.canShowCallout = YES;
    }

    annotationView = customPinView;
    [annotationView setEnabled:YES];
    [annotationView setCanShowCallout:YES];

    return annotationView;
}

在地图上加载 mkannotation 后，所有这些字幕都没有更新...... 怎么了？

感谢您的帮助...

Answer 1

这取决于您创建 MKAnnotations 的方式。

你应该有一个像“Place”这样的对象，由 Place.h 和 Place.m 表示，它符合 MKAnnotation 协议...

Place 会有一个类似的属性

float distance;

然后你的字幕方法（MKAnnotation 的一部分）会做这样的事情

- (NSString *)subtitle
{
    return [NSString stringWithFormat:@"%0.2f Miles Away", distance];
}

那个 subtitle 方法被 mapview 不断调用（实际上它被调用的频率几乎是荒谬的），所以一旦你操纵了距离的值，它就会反映在地图上（可能早在下一个您点击图钉的时间）。

Answer 2

当您更新标题时，您应该通知 MKAnnotationView 以最适合您需要的 KVO 方式更新标注视图，例如：

1. 为title和使用合成或实现setter

   self.title = @"new title";
   

2. 使用明确的 KVO 通知

   [self willChangeValueForKey:@"title"];
   [title release];
   title = [newTitle copy];
   [self didChangeValueForKey:@"title"];
   

字幕同上。