Question

我跟着Xamarin Tutorial Customizing a Map。我稍微改了一下，以便画一条路线。

public class CustomMap : Map
{
    public static readonly BindableProperty RouteCoordinatesProperty =
    BindableProperty.Create(nameof(RouteCoordinates), typeof(List<Position>), typeof(CustomMap), new List<Position>(), BindingMode.TwoWay);

    public List<Position> RouteCoordinates
    {
        get { return (List<Position>)GetValue(RouteCoordinatesProperty); }
        set { SetValue(RouteCoordinatesProperty, value); }
    }
}

WinPhone 8.1渲染器：

[assembly: ExportRenderer(typeof(CustomMap), typeof(CustomMapRenderer))]
namespace PROJECT.WinPhone
{
public class CustomMapRenderer : MapRenderer
{
    MapControl nativeMap;
    CustomMap formsMap;

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

        if (e.OldElement != null)
        {
            nativeMap = Control as MapControl;
        }

        if (e.NewElement != null)
        {
            formsMap = (CustomMap)e.NewElement;
            nativeMap = Control as MapControl;
            //UpdatePolyLine();

            var coordinates = new List<BasicGeoposition>();
            foreach (var position in formsMap.RouteCoordinates)
            {
                coordinates.Add(new BasicGeoposition() { Latitude = position.Latitude, Longitude = position.Longitude });
            }

            var polyline = new MapPolyline();
            polyline.StrokeColor = Windows.UI.Color.FromArgb(128, 255, 0, 0);
            polyline.StrokeThickness = 5;
            polyline.Path = new Geopath(coordinates);
            nativeMap.MapElements.Add(polyline);
        }
    }
}
}

polyline.Path = new Geopath（coordinates）; throws Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED)) 问题是我的另外两个渲染器（Android和iOS）工作..也许某些东西是不可能的，因为我使用WinPhone8.1不像教程，这是UWP

AndroidRenderer

[assembly: ExportRenderer(typeof(CustomMap), typeof(CustomMapRenderer))]
namespace PROJECT.Droid
{
public class CustomMapRenderer : MapRenderer, IOnMapReadyCallback
{
    GoogleMap map;
    Polyline polyline;

    protected override void OnElementChanged(Xamarin.Forms.Platform.Android.ElementChangedEventArgs<Xamarin.Forms.View> e)
    {
        base.OnElementChanged(e);

        if (e.OldElement != null)
        {
            // Unsubscribe
        }

        if (e.NewElement != null)
        {
            ((MapView)Control).GetMapAsync(this);
        }

        UpdatePolyLine();
    }

    protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);
        if (this.Element == null || this.Control == null)
            return;

        if (e.PropertyName == CustomMap.RouteCoordinatesProperty.PropertyName)
        {
            UpdatePolyLine();
        }
    }

    private void UpdatePolyLine()
    {
        if (map != null)
        {
            if (polyline != null)
            {
                polyline.Remove();
                polyline.Dispose();
            }
            var polylineOptions = new PolylineOptions();
            polylineOptions.InvokeColor(0x66FF0000);

            int a = 0;

            foreach (var position in ((CustomMap)this.Element).RouteCoordinates)
            {
                polylineOptions.Add(new LatLng(position.Latitude, position.Longitude));
            }

            polyline = map.AddPolyline(polylineOptions);
        }
    }

    public void OnMapReady(GoogleMap googleMap)
    {
        map = googleMap;
        UpdatePolyLine();
    }
}
}

iOSRenderer

[assembly: ExportRenderer(typeof(CustomMap), typeof(CustomMapRenderer))]
namespace PROJECT.iOS
{
public class CustomMapRenderer : MapRenderer
{
    MKMapView nativeMap;
    MKPolylineRenderer polylineRenderer;

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

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

        if (e.NewElement != null)
        {
            UpdatePolyLine();
        }
    }

    protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);
        if (this.Element == null || this.Control == null)
            return;

        if (e.PropertyName == CustomMap.RouteCoordinatesProperty.PropertyName)
        {
            UpdatePolyLine();
        }
    }

    MKOverlayRenderer GetOverlayRenderer(MKMapView mapView, IMKOverlay overlay)
    {
        if (polylineRenderer == null)
        {
            polylineRenderer = new MKPolylineRenderer(overlay as MKPolyline);
            polylineRenderer.FillColor = UIColor.Blue;
            polylineRenderer.StrokeColor = UIColor.Red;
            polylineRenderer.LineWidth = 3;
            polylineRenderer.Alpha = 0.4f;
        }
        return polylineRenderer;
    }

    private void UpdatePolyLine()
    {
        if (nativeMap != null)
        {
            var formsMap = ((CustomMap)this.Element);
            nativeMap = Control as MKMapView;

            nativeMap.OverlayRenderer = GetOverlayRenderer;

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

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

            var routeOverlay = MKPolyline.FromCoordinates(coords);
            nativeMap.AddOverlay(routeOverlay);
        }
    }
}
}

Answer 1

经过很长一段时间，我发现为什么它没有用......

如果您像我一样，如果您使用 Google Direction API 进行HttpRequest，那么结果将在{{1 }}

由于OnElementChanged()不是formsMap.RouteCoordinates但为空，因此会引发null ..

这是好的 Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED)) 用于PolyLine 使用

CustomMapRenderer

Xamarin.Forms.Maps - 灾难性故障（HRESULT异常：0x8000FFFF（E_UNEXPECTED））

1 个答案: