Xamarin表单-使用自定义地图渲染器的地图上的多个多边形

Question

我已经遵循了 Xamarin表单教程，该教程使用自定义地图渲染器突出显示地图上的区域。本教程介绍了如何在Xamarin Forms中向地图添加一个多边形，但没有说明如何扩展代码以在地图上允许多个多边形。

如何调整此实现以在iOS的地图上允许多个多边形？这是我的iOS代码：

[assembly: ExportRenderer(typeof(CustomMap), typeof(CustomMapRenderer))]
namespace MapOverlay.iOS
{
    public class CustomMapRenderer : MapRenderer
    {
        MKPolygonRenderer polygonRenderer;

        protected override void OnElementChanged(ElementChangedEventArgs<View> e)
        {
            base.OnElementChanged(e);

            if (e.OldElement != null) {
                var nativeMap = Control as MKMapView;
                if (nativeMap != null) {
                    nativeMap.RemoveOverlays(nativeMap.Overlays);
                    nativeMap.OverlayRenderer = null;
                    polygonRenderer = null;
                }
            }

            if (e.NewElement != null) {
                var formsMap = (CustomMap)e.NewElement;
                var nativeMap = Control as MKMapView;

                nativeMap.OverlayRenderer = GetOverlayRenderer;

                CLLocationCoordinate2D[] coords = new CLLocationCoordinate2D[formsMap.ShapeCoordinates.Count];

                int index = 0;
                foreach (var position in formsMap.ShapeCoordinates)
                {
                    coords[index] = new CLLocationCoordinate2D(position.Latitude, position.Longitude);
                    index++;
                }

                var blockOverlay = MKPolygon.FromCoordinates(coords);
                nativeMap.AddOverlay(blockOverlay);
            }
        }




 MKOverlayRenderer GetOverlayRenderer(MKMapView mapView, IMKOverlay overlayWrapper)
      {
          if (polygonRenderer == null && !Equals(overlayWrapper, null)) {
              var overlay = Runtime.GetNSObject(overlayWrapper.Handle) as IMKOverlay;
              polygonRenderer = new MKPolygonRenderer(overlay as MKPolygon) {
                  FillColor = UIColor.Red,
                  StrokeColor = UIColor.Blue,
                  Alpha = 0.4f,
                  LineWidth = 9
              };
          }
          return polygonRenderer;
      }

    }
}

Answer 1

您的代码有两个问题：

1. 第一个问题在您的if (e.NewElement != null){...}代码中。如果要具有多个多边形，formsMap.ShapeCoordinates则应为一种List<List<Position>>。因此它可以具有多个面的坐标组。如您的代码所示，它使用List<Position>。而且您的代码nativeMap.AddOverlay(blockOverlay);仅触发一次，这只会在地图中添加一个叠加层。

2. 更改if (polygonRenderer == null && !Equals(overlayWrapper, null))中GetOverlayRenderer来if (!Equals(overlayWrapper, null))。否则，每次地图添加叠加层并触发方法时，它将返回first polygonRenderer。

这是我的代码，例如：

1. PCL 中MainPage.xaml中的代码：

   <ContentPage.Content>
       <local:CustomMap x:Name="customMap" MapType="Street" WidthRequest="{x:Static local:App.ScreenWidth}" HeightRequest="{x:Static local:App.ScreenHeight}" />
   </ContentPage.Content>
   

2. 我在PCL的MainPage.xaml.cs中添加了两个多边形的位置列表：

   List<Position> pos = new List<Position> { new Position(39.939889, 116.423493), new Position(39.930622, 116.423924), new Position(39.930733,116.441135), new Position(39.939944, 116.44056) };
   List<Position> posi = new List<Position> { new Position(39.934633, 116.399921), new Position(39.929709, 116.400208), new Position(39.929792, 116.405994), new Position(39.934689,116.405526) };
   customMap.ShapeCoordinates.Add(pos);
   customMap.ShapeCoordinates.Add(posi);
   customMap.MoveToRegion(MapSpan.FromCenterAndRadius(new Position(39.934689, 116.405526), Distance.FromMiles(1.5)));
   

3. PCL 中CustomMap.cs中的代码：

   public class CustomMap : Map
   {
       public List<List<Position>> ShapeCoordinates { get; set; }
   
       public CustomMap()
       {
           ShapeCoordinates = new List<List<Position>>();
       }
   }
   

4. iOS平台中CustomMapRenderer.cs中的代码：

   class CustomMapRenderer : MapRenderer
   {
       MKPolygonRenderer polygonRenderer;
   
       protected override void OnElementChanged(ElementChangedEventArgs<View> e)
       {
           base.OnElementChanged(e);
   
           if (e.OldElement != null)
           {
               var nativeMap = Control as MKMapView;
               if (nativeMap != null)
               {
                   nativeMap.RemoveOverlays(nativeMap.Overlays);
                   nativeMap.OverlayRenderer = null;
                   polygonRenderer = null;
               }
           }
   
           if (e.NewElement != null)
           {
               var formsMap = (CustomMap)e.NewElement;
               var nativeMap = Control as MKMapView;
               nativeMap.OverlayRenderer = GetOverlayRenderer;
   
               foreach (List<Position> positionList in formsMap.ShapeCoordinates)
               {
   
                   CLLocationCoordinate2D[] coords = new CLLocationCoordinate2D[positionList.Count];
   
                   int index = 0;
                   foreach (var position in positionList)
                   {
                       coords[index] = new CLLocationCoordinate2D(position.Latitude, position.Longitude);
                       Console.WriteLine(position.Latitude +" : "+ position.Longitude);
   
                       index++;
                   }
   
   
   
                   var blockOverlay = MKPolygon.FromCoordinates(coords);
                   nativeMap.AddOverlay(blockOverlay);
   
               }
           }
       }
   
   
   
       MKOverlayRenderer GetOverlayRenderer(MKMapView mapView, IMKOverlay overlayWrapper)
       {
           if (!Equals(overlayWrapper, null))
           {         
               var overlay = Runtime.GetNSObject(overlayWrapper.Handle) as IMKOverlay;
               polygonRenderer = new MKPolygonRenderer(overlay as MKPolygon)
               {
                   FillColor = UIColor.Red,
                   StrokeColor = UIColor.Blue,
                   Alpha = 0.4f,
                   LineWidth = 9
   
               };
           }
           return polygonRenderer;
       }
   }
   

它是这样的：