MKAnnotation显示问题

MKMapView 中有一个标志针
点击标记针时可以看见标题和副标题，怎么样不需要点击标记让标题自动显示。
代码如下：

 self.mapView = [[[MKMapView alloc]init] autorelease];
    mapView.frame = self.view.bounds;
    mapView.delegate = self;
    [self.view addSubview:mapView];

    location = CLLocationCoordinate2DMake(lattitude, longitude);
    MKCoordinateRegion region = self.mapView.region;
    region.center = location;
    region.span.longitudeDelta = kSpan;
    region.span.latitudeDelta = kSpan;
    [self.mapView setRegion:region animated:YES];

    CustomMapAnnotation *newAnnotation = [[CustomMapAnnotation alloc] init];
    newAnnotation.title = @"Title";
    newAnnotation.subtitle = @"Subtitle";
    newAnnotation.accessibilityTraits = UIAccessibilityTraitButton;
    newAnnotation.coordinate = location;
    annotation = newAnnotation;
    [mapView addAnnotation:annotation];
    [newAnnotation release];

- (MKAnnotationView *) mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>) annotationDel
{
    MKPinAnnotationView *pinView = nil;

    static NSString *defaultPinID = @"mapPin";

    pinView = (MKPinAnnotationView *)[self.mapView dequeueReusableAnnotationViewWithIdentifier:defaultPinID];

    if (pinView == nil)
        pinView = [[[MKPinAnnotationView alloc] initWithAnnotation:annotationDel reuseIdentifier:defaultPinID] autorelease];

    pinView.pinColor = MKPinAnnotationColorRed;
    pinView.canShowCallout = YES;
    pinView.animatesDrop = YES;
    [pinView setSelected:YES];

    UIButton* rightButton = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
    [rightButton addTarget:self action:@selector(detailButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
    pinView.rightCalloutAccessoryView = rightButton;

    return pinView;

}

使用MKMapView的selectAnnotation:animated 方法

[mapView selectAnnotation:YorAnnotation animated:YES];