MapKit 自定义注释

Question

我对 iOS6 mapkit 有一些疑问。我试图创建a simple application that shows my current location and adds custom annotations to my MapView control。这是我的代码：

@interface MapViewAnnotation : NSObject<MKAnnotation>{}

@property (nonatomic, copy) NSString *title;
@property (nonatomic, readonly) CLLocationCoordinate2D cordinate;

- (id) initWithTitle:(NSString *) t coordinate:(CLLocationCoordinate2D) c;

@end

以及实现：

#import "MapViewAnnotation.h"
@implementation MapViewAnnotation
@synthesize title;
@synthesize coordinate;
- (id) initWithTitle:(NSString *) t coordinate:(CLLocationCoordinate2D) c{
    self = [super init];
    self.title = t;
    self.coordinate = c;
    return self;
}
@end

这是UIViewController：

#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
#import <MapKit/MapKit.h>
@interface ViewController : UIViewController <CLLocationManagerDelegate,MKMapViewDelegate>{}

@property (nonatomic, strong) IBOutlet MKMapView *mapView;
@property (nonatomic, strong) CLLocationManager *locationManager;
@end

还有.main 文件：

#import "ViewController.h"
#import "MapViewAnnotation.h"
@interface ViewController () @end
@implementation ViewController
@synthesize mapView, locationManager;
- (void)viewDidLoad{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    self.mapView.delegate = self;

    self.locationManager = [[CLLocationManager alloc] init];
    [locationManager setDelegate:self];

    [locationManager setDistanceFilter:kCLDistanceFilterNone];
    [locationManager setDesiredAccuracy:kCLLocationAccuracyBest];

    [self.mapView setShowsUserLocation:YES];

    CLLocationCoordinate2D location;
    location.latitude = 37.78608;
    location.longitude = -122.405398;

    MapViewAnnotation *mapAnnotation = [[MapViewAnnotation alloc] initWithTitle:@"Store location" coordinate:location];
    [self.mapView addAnnotation:mapAnnotation];
}
-(void) mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)views{
    MKAnnotationView *annotationView = [views objectAtIndex:0];
    id<MKAnnotation> mp = [annotationView annotation];

    MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance([mp coordinate], 250, 250);
    [self.mapView setRegion:region animated:YES];
}
@end

它成功显示了我当前的位置，但是当我在 viewDidLoad 中使用这一行时：

MapViewAnnotation *mapAnnotation = [[MapViewAnnotation alloc] initWithTitle:@"Store location" coordinate:location];

我得到了这个例外：

MapKitDemo[3426:c07] -[MapViewAnnotation setCoordinate:]: unrecognized selector sent to instance 0x8551ae0
2012-10-03 16:19:23.070 MapKitDemo[3426:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MapViewAnnotation setCoordinate:]: unrecognized selector sent to instance 0x8551ae0'

我做错了什么？

Answer 1

您在子类的 -initWithTitle:coordinate: 方法中使用属性 self.coordinate，这意味着使用属性而不是 iVar 设置坐标，因为此属性设置为 readonly，所以您是收到此错误并可能崩溃...

您必须像这样直接访问 iVar：

#import "MapViewAnnotation.h"
@implementation MapViewAnnotation

@synthesize title = _title, coordinate = _coordinate    

- (id) initWithTitle:(NSString *) t coordinate:(CLLocationCoordinate2D) c{
    self = [super init];
    if(self){
        _title = t;
        _coordinate = c;
        // self.coordinate = c /* !This is readonly ! */
    }
    return self;
}
@end

请注意，我还更改了@synthesize（这不再是必需的了——我相信这是从 Xcode 4.5 开始自动完成的？也许是更早的版本）。另请注意，我在您的初始化中做了一个条件，您应该这样做，以确保在[super init] 无法初始化您的对象的情况下，您不会尝试在 nil 上设置属性/iVars。

Answer 2

坐标是只读属性。您不能为此使用设置器。使用 ivar 或使其读/写。