objective-c - 注释在 MapKit 、 iOS 上不显示标题/副标题

Question

我正在解析一些带有一些兴趣点的数据，并尝试使用 MapKit 框架在 map 上显示它们。我为 map 上的对象创建了一个自定义类，我称之为 MyLocation。

MyLocation.h:

#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>

@interface MyLocation : NSObject <MKAnnotation> {
    NSString *_name;
    NSString *_address;
    NSInteger _eventId;
    CLLocationCoordinate2D _coordinate;
    NSString *title;
    NSString *subtitle;

}

@property (nonatomic , copy) NSString *name;
@property (nonatomic , copy) NSString *address;
@property (nonatomic, assign) NSInteger eventId;
@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;
@property (nonatomic, copy) NSString *title;
@property (nonatomic, copy) NSString *subtitle;

- (id)initWithName:(NSString*)name address:(NSString*)address coordinate:(CLLocationCoordinate2D)coordinate;

@end

我的位置.m:

#import "MyLocation.h"

@implementation MyLocation
@synthesize name = _name;
@synthesize eventId=_eventId;
@synthesize address = _address;
@synthesize coordinate = _coordinate;
@synthesize title;
@synthesize subtitle;



- (id)initWithName:(NSString*)name address:(NSString*)address coordinate:(CLLocationCoordinate2D)coordinate {
    if ((self = [super init])) {
        _name= [name copy];
        _address = [address copy];
        _coordinate = coordinate;
    }
    return self;
}

- (NSString *)title {
    if ([_name isKindOfClass:[NSNull class]]) {
        NSLog(@"11111111");
        return @"Unknown charge";
    }
    else{
        NSLog(@"222222");
        return _name;

    }
}

- (NSString *)subtitle {
    NSLog(@"HAHAHAHAA");
    return _address;
}

@end

然后在我的 viewController 上我这样做:

//showing on map the points of interests that are stored on "eventList"
int i=0;
for (parsedItem *event in self.eventsList) {
    CLLocationCoordinate2D coordinate;
    coordinate.latitude = event.latitude;
    coordinate.longitude = event.longitude;
    if(i==0){
        //numbers show map zoom. 500,500 = map stretches 500 meters to the North and the South of current location
        MKCoordinateRegion region =
        MKCoordinateRegionMakeWithDistance (coordinate,1000,1000);
        [mapView setRegion:region animated:NO];
    }
    MyLocation *eventAnnotation = [[MyLocation alloc] initWithName:event.typeEvent address:event.titleEvent coordinate:coordinate] ;        
    eventAnnotation.name = event.typeEvent;
    eventAnnotation.address = event.titleEvent;
    eventAnnotation.eventId = i;
    i++;        
    [mapView addAnnotation:eventAnnotation];
} 

后来我使用更多代码为注释提供图像，所有内容都显示在 map 上，但是如果我单击注释，我看不到带有标题和副标题的窗口。我只看到注释，但没有单击它们时应该获得的额外信息。

我猜这行代码有问题:

MyLocation *eventAnnotation = [[MyLocation alloc] initWithName:event.typeEvent address:event.titleEvent coordinate:coordinate] ;

有什么想法吗？

编辑

只是补充一点，我也使用这个功能:

- (MKAnnotationView *)mapView:(MKMapView *)mapView2 viewForAnnotation:(id <MKAnnotation>)annotation {

    static NSString *identifier = @"MyLocation";   
    if ([annotation isKindOfClass:[MyLocation class]]) {
        NSLog(@"I got into the class!!!");
        MKPinAnnotationView *annotationView = (MKPinAnnotationView *) [mapView dequeueReusableAnnotationViewWithIdentifier:identifier];
        if (annotationView == nil) {
            annotationView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:identifier];
        } else {
            annotationView.annotation = annotation;
        }

        annotationView.enabled = YES;
        annotationView.canShowCallout = YES;
        MyLocation *eventAnnotation=annotation;


        if ([eventAnnotation.address isEqualToString: @"Culture_07/02/2012"]) {
            NSLog(@"Mphkeeee");
            annotationView.image=[UIImage imageNamed:@"culture.png"];
            //annotation.title = @"Holla!";
        } else if ([eventAnnotation.address isEqualToString: @"Sports_06/29/2012"]) {
            annotationView.image=[UIImage imageNamed:@"sports.png"];
        } else if ([eventAnnotation.address isEqualToString: @"Accident_06/29/2012"]) {
            annotationView.image=[UIImage imageNamed:@"accident.png"];
        } else if ([eventAnnotation.address isEqualToString: @"Problem_06/29/2012"]) {
            annotationView.image=[UIImage imageNamed:@"problem.png"];
        } else if ([eventAnnotation.address isEqualToString: @"Traffic_07/02/2012"]) {
            annotationView.image=[UIImage imageNamed:@"traffic.png"];
        } else if ([eventAnnotation.address isEqualToString: @"Music_06/29/2012"]) {
            annotationView.image=[UIImage imageNamed:@"music.png"];
        } 

        return annotationView;

    }

    return nil;    
}

Answer 1

对 title 和 subtitle 使用自定义 getter 方法，而不是显式设置这些属性，这对于 map View 来说是没问题的。

您的标注未显示的原因是 title (返回 _name - 设置为 event.typeEvent)返回一个 nil 或空字符串。

您的 getter 方法正在检查 _name 是否属于 NSNull 类型，但它可能是 NSString 并且仍然是 nil 或空字符串。

当 title 为 nil 或空字符串时，注释将不会显示标注(即使 canShowCallout 设置为 是，即使 subtitle 返回非空值)。

因此，typeEvent 很可能是 nil 或空字符串。