如何在Xamarin.Forms.Maps中自定义MkMapView标注/视图

using MapKit;

public class CustomAnnotation : MKAnnotation
{
    public override string Title { get; }
    public override string Subtitle { get; }
    public override CLLocationCoordinate2D Coordinate { get; }

    public CustomAnnotation(string title, string subtitle, CLLocationCoordinate2D coordinate)
    {
        Title = title;
        Subtitle = subtitle;
        Coordinate = coordinate;
    }
}

using Xamarin.Forms.Maps.iOS;
using Xamarin.Forms.Platform.iOS;
using MapKit;
using UIKit;

[assembly: ExportRenderer(typeof(Xamarin.Forms.Maps.Map), typeof(CustomMapRenderer))]
public class CustomMapRenderer : MapRenderer
{
    protected override void OnElementChanged(ElementChangedEventArgs<View> e)
    {
        base.OnElementChanged(e);

        if (Control != null)
        {
            var nativeMap = Control as MKMapView;
            nativeMap.GetViewForAnnotation += GetViewForAnnotation;
        }
    }

    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);

        if (e.PropertyName == Xamarin.Forms.Maps.Map.MapProperty.PropertyName)
        {
            var nativeMap = Control as MKMapView;
            nativeMap.GetViewForAnnotation += GetViewForAnnotation;
        }
    }

    private MKAnnotationView GetViewForAnnotation(MKMapView mapView, IMKAnnotation annotation)
    {
        if (annotation is CustomAnnotation customAnnotation)
        {
            var annotationView = mapView.DequeueReusableAnnotation("customAnnotation") as MKPinAnnotationView;
            if (annotationView == null)
            {
                annotationView = new MKPinAnnotationView(annotation, "customAnnotation");
                annotationView.PinTintColor = UIColor.Green;
                annotationView.CanShowCallout = true;
            }
            else
            {
                annotationView.Annotation = annotation;
            }

            return annotationView;
        }

        return null;
    }
}

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:maps="clr-namespace:Xamarin.Forms.Maps;assembly=Xamarin.Forms.Maps"
             x:Class="YourNamespace.MainPage">
    <maps:Map>
        <maps:Map.MapElements>
            <maps:CustomPin Position="37,-122" Label="Custom Pin" />
        </maps:Map.MapElements>
    </maps:Map>
</ContentPage>