标题显示按钮不会出现

Question

rob为我的问题推荐了一个新帖子。在标题中，我的“canShowCallout按钮”无法正常工作。

这是我的代码的主要部分：

//
//  ThirdViewController.m
//

#import "ThirdViewController.h"
#import <MapKit/MapKit.h>
#import "Parser.h"
#import <CoreLocation/CoreLocation.h>

#define kURL @"http://localhost/kmlnew_beta.kml"

@implementation ThirdViewController


- (void)viewDidLoad
{
    NSURL *url = [NSURL URLWithString:kURL];
    [self loadKml:url];
    follow = FALSE;
}

- (void)loadKml:(NSURL *)url
{
    // parse the kml

    Parser *parser = [[Parser alloc] initWithContentsOfURL:url];
    parser.rowElementName = @"Placemark";
    parser.elementNames = @[@"name", @"Snippet", @"coordinates", @"description"];
    parser.attributeNames = nil;
    [parser parse];

    // add annotations for each of the entries

    for (NSDictionary *locationDetails in parser.items)
    {
        MKPointAnnotation *annotation = [[MKPointAnnotation alloc] init];
        annotation.title = locationDetails[@"name"];
        annotation.subtitle = locationDetails[@"Snippet"];
        NSArray *coordinates = [locationDetails[@"coordinates"] componentsSeparatedByString:@","];
        annotation.coordinate = CLLocationCoordinate2DMake([coordinates[1] floatValue], [coordinates[0] floatValue]);
        [self.mapView addAnnotation:annotation];
    }

    // update the map to focus on the region that encompasses all of your annotations

    MKCoordinateRegion region;
    if ([self.mapView.annotations count] > 1)
    {
        region = [self regionForAnnotations:self.mapView.annotations];
        region = MKCoordinateRegionMake(region.center, MKCoordinateSpanMake(region.span.latitudeDelta * 1.05, region.span.longitudeDelta * 1.05));  // expand the region by 5%
    }
    else
    {
        id<MKAnnotation> annotation = self.mapView.annotations[0];
        region = MKCoordinateRegionMakeWithDistance(annotation.coordinate, 100.0, 100.0);
    }
    [self.mapView setRegion:region animated:YES];
}

- (MKCoordinateRegion)regionForAnnotations:(NSArray *)annotations {

    CLLocationDegrees minLat = 90.0;
    CLLocationDegrees maxLat = -90.0;
    CLLocationDegrees minLon = 180.0;
    CLLocationDegrees maxLon = -180.0;

    for (id <MKAnnotation> annotation in annotations) {
        if (annotation.coordinate.latitude < minLat) {
            minLat = annotation.coordinate.latitude;
        }
        if (annotation.coordinate.longitude < minLon) {
            minLon = annotation.coordinate.longitude;
        }
        if (annotation.coordinate.latitude > maxLat) {
            maxLat = annotation.coordinate.latitude;
        }
        if (annotation.coordinate.longitude > maxLon) {
            maxLon = annotation.coordinate.longitude;
        }
    }

    MKCoordinateSpan span = MKCoordinateSpanMake(maxLat - minLat, maxLon - minLon);

    CLLocationCoordinate2D center = CLLocationCoordinate2DMake((maxLat - span.latitudeDelta / 2), maxLon - span.longitudeDelta / 2);

    return MKCoordinateRegionMake(center, span);
}

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    if ([annotation isKindOfClass:[MKUserLocation class]]){
        return nil;
    }
    else{
    MKPinAnnotationView *annotationView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"loc"];
    annotationView.canShowCallout = YES;


//    annotationView.rightCalloutAccessoryView = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
    UIButton *detailButton = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
    //NSInteger annotationValue = [self.annotations indexOfObject:annotation];

    [detailButton addTarget:self action:@selector(showDetailView:) forControlEvents:UIControlEventTouchUpInside];
    annotationView.rightCalloutAccessoryView=detailButton;
    annotationView.enabled = YES;
//    return annotationView;
    return annotationView;
    }
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)PosBtn:(id)sender
{
    [self locate];
}

- (void)locate
{

    [_mapView setCenterCoordinate:_mapView.userLocation.coordinate];
    MKCoordinateRegion region;
    region.center.latitude = _mapView.userLocation.coordinate.latitude;
    region.center.longitude = _mapView.userLocation.coordinate.longitude;
    region.span.latitudeDelta = 0.02;
    region.span.longitudeDelta = 0.02;
    region = [_mapView regionThatFits:region];
    [_mapView setRegion:region animated:TRUE];

    NSLog(@"Tracking");

}

如果有更好的代码建议，我很高兴收到这个

我有什么：

它有点人满为患，但确切地说明了我拥有的东西。 rightCalloutAccessoryView遗失了。有什么想法吗？

最好的问候CTS

编辑：有时我会收到此错误，但我不知道它的意思和不起作用：

 <GEOTileSource: 0x847fdc0>: Error downloading tiles Server Error: Error Domain=GEOErrorDomain Code=-204 "The operation couldn’t be completed. (GEOErrorDomain error -204.)" UserInfo=0x1f12ae70 {UnderlyingErrors=(
    "Error Domain=GEOErrorDomain Code=-204 \"The operation couldn\U2019t be completed. (GEOErrorDomain error -204.)\""
)}