更新MKAnnotationview的UILabel-Subview

Question

我有一个带有集群注释的MapView（ADMapCluster）。 I want to show the amount of elements in the Cluster，因此我将一个UILabel添加到MKAnnotationView 作为子视图。

  

我的问题是当我在缩放后重复使用MKAnnotationView时   UILabel不会更新文本。

- (MKAnnotationView *)mapView:(ADClusterMapView *)mapView viewForClusterAnnotation:(id<MKAnnotation>)annotation {
if ([annotation isKindOfClass:[MKUserLocation class]])
    return nil;

MKAnnotationView * pinView = (MKAnnotationView *)[mapView dequeueReusableAnnotationViewWithIdentifier:@"ADMapCluster"];
if (!pinView) {
    pinView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"ADMapCluster"];
    pinView.image = [UIImage imageNamed:@"map-markers"];
    UILabel *countLabel = [[UILabel alloc] initWithFrame:CGRectMake(2, 5, 25, 20)];
    countLabel.textAlignment = NSTextAlignmentCenter;
    [countLabel setTag:2];
    countLabel.text = [NSString stringWithFormat:@"%d",[[(ADClusterAnnotation*)pinView.annotation originalAnnotations] count] ];
    countLabel.font = [UIFont fontWithName:@"Avenir-Book" size:10];
    [pinView addSubview:countLabel];

}
else {
    pinView.annotation = annotation;
    [((UILabel*)[pinView viewWithTag:2]) setText:[NSString stringWithFormat:@"%d",[[(ADClusterAnnotation*)pinView.annotation originalAnnotations] count] ]];
    [((UILabel*)[pinView viewWithTag:2]) setNeedsDisplay];
}
return pinView;

}

知道我做错了什么以及为什么标签没有更新？