找不到自定义地图图钉

Question

我有一个 Xamarin Forms 地图应用程序，我正在使用适用于 Android 的此文档的自定义地图渲染器。 我成功地构建了一个引脚。 现在我想制作几个引脚，因此为了减少代码的重复性，我将我的数据（示例数据）添加到 Mydata.json 文件中并使其从中读取。然而，只有一个引脚数据有效，并且在许多情况下，应用程序仅考虑最后一个引脚数据。 这是 data.json：

[

{"Label"   :"Country1",
        "Address":"A multine paragraph",
        "Lat":"-12",
        "Lng":"14",
        "Name":"Tamarin",
         "Url": "http://xamarin.com/about/"
},


{ "Label"  :"Country2",
        "Address":"Multiline paragraph",
        "Lat":"-25", 
        "Lng":"45",
        "Name":"Camarin",
        "Url": "http://xamarin.com/about/"
},

{ "Label"  :"Country3",
         "Address":"Multiline paragraphMultiline paragraphMultiline paragraphMultiline paragraphMultiline paragraphMultiline paragraphMultiline paragraphMultiline paragraph",
         "Lat":"-5", 
         "Lng":"45",
         "Name":"Xamarin",
         "Url": "http://xamarin.com/about/"
}

]

这是我的 CustomMapRenderer：

using System;
using System.Collections.Generic;
using Android.Content;
using Android.Gms.Maps;
using Android.Gms.Maps.Model;
using Android.Widget;
using Orbage;
using Orbage.Droid;
using Xamarin.Forms;
using Xamarin.Forms.Maps;
using Xamarin.Forms.Maps.Android;

[assembly: ExportRenderer(typeof(CustomMap), typeof(CustomMapRenderer))]
namespace Orbage.Droid
{
    public class CustomMapRenderer : MapRenderer, GoogleMap.IInfoWindowAdapter
    {
        List<CustomPin> customPins;

        public CustomMapRenderer(Context context) : base(context)
        {
        }

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

            if (e.OldElement != null)
            {
                NativeMap.InfoWindowClick -= OnInfoWindowClick;
            }

            if (e.NewElement != null)
            {
                var formsMap = (CustomMap)e.NewElement;
                customPins = formsMap.CustomPins;
            }
        }

        protected override void OnMapReady(GoogleMap map)
        {
            base.OnMapReady(map);

            NativeMap.InfoWindowClick += OnInfoWindowClick;
            NativeMap.SetInfoWindowAdapter(this);
        }

        protected override MarkerOptions CreateMarker(Pin pin)
        {
            var marker = new MarkerOptions();
            marker.SetPosition(new LatLng(pin.Position.Latitude, pin.Position.Longitude));
            marker.SetTitle(pin.Label);
            marker.SetSnippet(pin.Address);
            marker.SetIcon(BitmapDescriptorFactory.FromResource(Resource.Drawable.pin));
            return marker;
        }

        void OnInfoWindowClick(object sender, GoogleMap.InfoWindowClickEventArgs e)
        {
            var customPin = GetCustomPin(e.Marker);
            if (customPin == null)
            {
                throw new Exception("Custom pin not found");
            }

            if (!string.IsNullOrWhiteSpace(customPin.Url))
            {
                var url = Android.Net.Uri.Parse(customPin.Url);
                var intent = new Intent(Intent.ActionView, url);
                intent.AddFlags(ActivityFlags.NewTask);
                Android.App.Application.Context.StartActivity(intent);
            }
        }

        public Android.Views.View GetInfoContents(Marker marker)
        {
            var inflater = Android.App.Application.Context.GetSystemService(Context.LayoutInflaterService) as Android.Views.LayoutInflater;
            if (inflater != null)
            {
                Android.Views.View view;

                var customPin = GetCustomPin(marker);
                if (customPin == null)
                {
                    throw new Exception("Custom pin not found");
                }

                if (customPin.Name.Equals("Xamarin"))
                {
                    view = inflater.Inflate(Resource.Layout.XamarinMapInfoWindow, null);
                }
                else
                {
                    view = inflater.Inflate(Resource.Layout.MapInfoWindow, null);
                }

                var infoTitle = view.FindViewById<TextView>(Resource.Id.InfoWindowTitle);
                var infoSubtitle = view.FindViewById<TextView>(Resource.Id.InfoWindowSubtitle);

                if (infoTitle != null)
                {
                    infoTitle.Text = marker.Title;
                }
                if (infoSubtitle != null)
                {
                    infoSubtitle.Text = marker.Snippet;
                }

                return view;
            }
            return null;
        }

        public Android.Views.View GetInfoWindow(Marker marker)
        {
            return null;
        }

        CustomPin GetCustomPin(Marker annotation)
        {
            var position = new Position(annotation.Position.Latitude, annotation.Position.Longitude);
            foreach (var pin in customPins)
            {
                if (pin.Position == position)
                {
                    return pin;
                }
            }
            return null;
        }
    }
}

我设置密码的位置：

using System;
using System.Collections.Generic;
using System.Text;
using Xamarin.Forms.Maps;

namespace Orbage
{
    public class CustomPin : Pin
    {
        public string Name { get; set; }
        public string Url { get; set; }
    }
}

其余代码只是 Microsoft 文档的逐步改编，但是，如果我误判了分析问题所需的代码量，请告诉我。

如您所见，从第 82 行开始，第二个异常结果为 true；即自定义引脚为空；但该引脚存在于数据文件中，并且由于某种原因无法读取它，我无法找出原因。我相信这与对象引用有关，但我找不到问题所在。 对于任何明显的原因（如果有的话），我提前表示歉意；因为我对此不太熟悉 谢谢。

Answer 1

感谢@Jason 的评论，以及来自here的这篇文章，我找到了问题所在。

customMap.CustomPins = new List<CustomPin> { pin };

这是我的 MapPage.xaml.cs 中的 foreach 内部：

foreach (var place in places)
            {
              CustomPin pin = new CustomPin
               {
                 Type = PinType.Place,
                 Position = new Position(Double.Parse(place.Lat), Double.Parse(place.Lng)),
                Label = place.Label,
                 Address = place.Address,
                 Name = place.Name,
                 Url = place.Url
             };
              customMap.CustomPins = new List<CustomPin> { pin }; //This one
              customMap.Pins.Add(pin);
              customMap.MoveToRegion(MapSpan.FromCenterAndRadius(new Position(37.79752, -122.40183), Distance.FromMiles(1.0)));

通过将其放在外面，它可以调用每个引脚。

 List<CustomPin> custompinList = new List<CustomPin>(); //Outside the foreach now
 foreach (var place in places)
 {
     CustomPin pin = new CustomPin
     {
         Type = PinType.Place,
         Position = new Position(Double.Parse(place.Lat), Double.Parse(place.Lng)),
         Label = place.Label,
         Address = place.Address,
         Name = place.Name,
         Url = place.Url
     };
     custompinList.Add(pin);
     customMap.Pins.Add(pin);
     customMap.MoveToRegion(MapSpan.FromCenterAndRadius(new Position(37.79752, -122.40183), Distance.FromMiles(1.0)));
 }

问题就解决了。