Xamarin.iOS :如何在苹果地图中更改注解别针颜色

using MapKit;
using UIKit;

public class CustomAnnotationView : MKAnnotationView
{
    private UIColor pinColor;

    public UIColor PinColor
    {
        get { return pinColor; }
        set
        {
            pinColor = value;
            SetNeedsDisplay();
        }
    }

    public CustomAnnotationView(IMKAnnotation annotation, string reuseIdentifier) : base(annotation, reuseIdentifier)
    {
        pinColor = UIColor.Red; // 设置默认颜色为红色
    }

    public override void Draw(CoreGraphics.CGRect rect)
    {
        base.Draw(rect);

        // 绘制自定义的别针图标
        UIImage pinImage = UIImage.FromBundle("pin_icon.png");
        pinImage.Draw(new CoreGraphics.CGPoint(0, 0));

        // 根据颜色填充别针图标
        using (CGContext context = UIGraphics.GetCurrentContext())
        {
            context.SetFillColor(pinColor.CGColor);
            context.FillRect(rect);
        }
    }

    public override void SetSelected(bool selected, bool animated)
    {
        base.SetSelected(selected, animated);

        // 根据选中状态来更改别针颜色
        if (selected)
        {
            pinColor = UIColor.Blue;
        }
        else
        {
            pinColor = UIColor.Red;
        }

        SetNeedsDisplay();
    }
}

public class MapViewController : UIViewController
{
    private MKMapView mapView;

    public override void ViewDidLoad()
    {
        base.ViewDidLoad();

        mapView = new MKMapView(View.Bounds);
        mapView.AutoresizingMask = UIViewAutoresizing.FlexibleDimensions;
        View.AddSubview(mapView);

        // 添加自定义的注解别针
        CLLocationCoordinate2D coordinate = new CLLocationCoordinate2D(37.785834, -122.406417);
        MKPointAnnotation annotation = new MKPointAnnotation();
        annotation.Coordinate = coordinate;
        mapView.AddAnnotation(annotation);
    }

    public override MKAnnotationView GetViewForAnnotation(MKMapView mapView, IMKAnnotation annotation)
    {
        if (annotation is MKPointAnnotation)
        {
            CustomAnnotationView annotationView = mapView.DequeueReusableAnnotation("CustomAnnotation") as CustomAnnotationView;
            if (annotationView == null)
            {
                annotationView = new CustomAnnotationView(annotation, "CustomAnnotation");
            }
            else
            {
                annotationView.Annotation = annotation;
            }
            return annotationView;
        }
        return null;
    }
}