如何在当前位置附近加载引脚并在缩小 Xamarin.Forms.Maps 时加载更多

Question

I'm trying to show pins on the map but only the ones that can fit the screen around your current location depending on the zoom level I've set on when the map appears, because I have 10's of pins and when I open the map it loads every pin and takes a long time to load.

Any idea on how to do it?

Method to load pins:

    async Task ExecuteLoadPinsCommand()
    {
        IsBusy = true;

        try
        {
            Map.Pins.Clear();
            Map.MapElements.Clear();
            Map.CustomPins.Clear();
            var contents = await placeRepository.GetAllPlacesWithoutRelatedDataAsync();

            if (contents == null || contents.Count < 1)
            {
                await App.Current.MainPage.DisplayAlert("No places found", "No places have been found for that category, please try again later", "Ok");
                await ExecuteLoadPinsCommand();
            }

            if (contents != null)
            {
                places.Clear();
                var customPins = this.Map.CustomPins;
                places = contents;
                foreach (var item in places)
                {
                    CustomPin devicePin = new CustomPin
                    {
                        Type = PinType.Place,
                        PlaceId = item.PlaceId.ToString(),
                        Position = new Position(item.Latitude, item.Longitude),
                        Label = $"{item.Name}",
                        Address = $"{item.Name}"
                    };

                    Map.CustomPins.Add(devicePin);
                    Map.Pins.Add(devicePin);
                }
            }
        }
        catch (Exception ex)
        {
            Debug.WriteLine(ex);
        }
        finally
        {
            IsBusy = false;
        }
    }

CustomMapRenderer:

    protected override MarkerOptions CreateMarker(Pin pin)
    {
        CustomPin pin = (CustomPin)pin;
        var thePlace = Task.Run(async () => await placeRepository.GetPlaceByIdWithMoodAndEventsAsync(Guid.Parse(pin.PlaceId)));
        var place = thePlace.ConfigureAwait(true)
                            .GetAwaiter()
                            .GetResult();

        var marker = new MarkerOptions();

        marker.SetPosition(new LatLng(place.Position.Latitude, place.Position.Longitude));
        if (place.Category == "" && place.SomethingCount == 0)
        {
            marker.SetIcon(BitmapDescriptorFactory.FromResource(Resource.Drawable.icon));
        }
        //else if ...

        return marker;

    }

Answer 1

Try this approach. Create the map WITH its pins, BEFORE displaying it.

using Xamarin.Forms;
using Xamarin.Forms.Maps;

namespace XFSOAnswers
{
    // Based on https://github.com/xamarin/xamarin-forms-samples/blob/main/WorkingWithMaps/WorkingWithMaps/WorkingWithMaps/PinPageCode.cs
    public class PinPageCode : ContentPage
    {
        public PinPageCode()
        {
            Title = "Pins demo";

            Position position = new Position(36.9628066, -122.0194722);
            MapSpan mapSpan = new MapSpan(position, 0.01, 0.01);

            Map map = new Map(mapSpan);

            Pin pin = new Pin
            {
                Label = "Santa Cruz",
                Address = "The city with a boardwalk",
                Type = PinType.Place,
                Position = position
            };
            map.Pins.Add(pin);
            // ... more pins.

            Content = new StackLayout
            {
                Margin = new Thickness(10),
                Children =
                {
                    map
                }
            };
        }
    }
}