selectAnnotation不显示标注

title

subtitle

@interface MyAnnotation : NSObject <MKAnnotation> {
    NSString *title;
    NSString *subtitle;
}

@property (nonatomic, copy) NSString *title;
@property (nonatomic, copy) NSString *subtitle;

@end

#import \"MyAnnotation.h\"

@implementation MyAnnotation

@synthesize title, subtitle;

@end

MyAnnotation *foo = [[MyAnnotation alloc] init];
foo.title = @\"I am Foo\";
foo.subtitle = \"I am jus\' a subtitle\";

-(MKAnnotationView *)mapView:(MKMapView *)_mapView viewForAnnotation:(id<MKAnnotation>)annotation
{
    static NSString *AnnotationViewIdentifier = @\"AnnotationViewIdentifier\";

    MKPinAnnotationView *annotationView = (MKPinAnnotationView *)[_mapView  dequeueReusableAnnotationViewWithIdentifier:AnnotationViewIdentifier];
    if (annotationView == nil) 
    {
       annotationView = [[[MKPinAnnotationView alloc]initWithAnnotation:annotation reuseIdentifier:AnnotationViewIdentifier]autorelease];
    }

    annotationView.canShowCallout = YES;

    return annotationView;
}