[Maps] [Android] [Regression] Registering for CameraMove events in a custom MapHandler disables Map.VisibleRegion.Center

[japarson]

Description

Create a custom map class and a handler for it, and inside that handler register for CameraMove events from the underlying GoogleMap (either via SetOnCameraMoveListener or the CameraMove event). When you do this, the Maui Map's VisibleRegion property no longer updates when you move the map. In particular, the Center property always returns the map's initial location.

Comment out the += to the CameraMove event, or the call to SetOnCameraMoveListener, and VisibleRegion.Center will update again. This is very broken, and it is a regression from Xamarin.Forms.

Steps to Reproduce

class CustomMapHandler : MapHandler
{
    protected override void ConnectHandler(Android.Gms.Maps.MapView platformView)
    {
        base.ConnectHandler(platformView);
        platformView.GetMapAsync(new CustomMapCallbackHandler(this));
    }

    internal void OnMapReady(Android.Gms.Maps.GoogleMap googleMap)
    {
        googleMap.CameraMove += this.OnCameraMoved;
    }

    void OnCameraMoved(object sender, EventArgs e)
    {
    }
}

class CustomMapCallbackHandler : Java.Lang.Object, Android.Gms.Maps.IOnMapReadyCallback
{
    readonly CustomMapHandler handler;

    public CustomMapCallbackHandler(CustomMapHandler handler)
    {
        this.handler = handler;
    }

    public void OnMapReady(Android.Gms.Maps.GoogleMap map)
    {
        this.handler.OnMapReady(map);
    }
}

Relevant Files

• src/Core/maps/src/Handlers/Map/MapHandler.cs
• src/Core/maps/src/Handlers/Map/MapHandler.Android.cs
• src/Controls/Maps/src/HandlerImpl/Map.Impl.cs
• src/Controls/Maps/src/Map.cs

Checklist

• Modify src/Core/maps/src/Handlers/Map/MapHandler.Android.cs ! No changes made Edit
• Running GitHub Actions for src/Core/maps/src/Handlers/Map/MapHandler.Android.cs ✗ Edit
• Modify src/Core/maps/src/Handlers/Map/MapHandler.cs ✓ 3d956e2 Edit
• Running GitHub Actions for src/Core/maps/src/Handlers/Map/MapHandler.cs ✓ Edit
• Modify src/Controls/Maps/src/Map.cs ! No changes made Edit
• Running GitHub Actions for src/Controls/Maps/src/Map.cs ✗ Edit

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Step 1: 🔎 Searching

I found the following snippets in your repository. I will now analyze these snippets and come up with a plan.

Some code snippets I think are relevant in decreasing order of relevance (click to expand). If some file is missing from here, you can mention the path in the ticket description.

maui/src/Core/maps/src/Handlers/Map/MapHandler.cs

Lines 1 to 55 in ab2c30a

	#if __IOS__ || MACCATALYST
	using PlatformView = Microsoft.Maui.Maps.Platform.MauiMKMapView;
	#elif MONOANDROID
	using PlatformView = Android.Gms.Maps.MapView;
	#elif WINDOWS
	using PlatformView = Microsoft.UI.Xaml.FrameworkElement;
	#elif TIZEN
	using PlatformView = Tizen.NUI.BaseComponents.View;
	#elif (NETSTANDARD || !PLATFORM) || (NET6_0 && !IOS && !ANDROID && !TIZEN)
	using PlatformView = System.Object;
	#endif
	using Microsoft.Maui.Handlers;
	namespace Microsoft.Maui.Maps.Handlers
	{
	public partial class MapHandler : IMapHandler
	{
	public static IPropertyMapper<IMap, IMapHandler> Mapper = new PropertyMapper<IMap, IMapHandler>(ViewHandler.ViewMapper)
	{
	[nameof(IMap.MapType)] = MapMapType,
	[nameof(IMap.IsShowingUser)] = MapIsShowingUser,
	[nameof(IMap.IsScrollEnabled)] = MapIsScrollEnabled,
	[nameof(IMap.IsTrafficEnabled)] = MapIsTrafficEnabled,
	[nameof(IMap.IsZoomEnabled)] = MapIsZoomEnabled,
	[nameof(IMap.Pins)] = MapPins,
	[nameof(IMap.Elements)] = MapElements,
	};
	public static CommandMapper<IMap, IMapHandler> CommandMapper = new(ViewCommandMapper)
	{
	[nameof(IMap.MoveToRegion)] = MapMoveToRegion,
	[nameof(IMapHandler.UpdateMapElement)] = MapUpdateMapElement,
	};
	public MapHandler() : base(Mapper, CommandMapper)
	{
	}
	public MapHandler(IPropertyMapper? mapper = null, CommandMapper? commandMapper = null)
	: base(mapper ?? Mapper, commandMapper ?? CommandMapper)
	{
	}
	IMap IMapHandler.VirtualView => VirtualView;
	PlatformView IMapHandler.PlatformView => PlatformView;
	public static void MapUpdateMapElement(IMapHandler handler, IMap map, object? arg)
	{
	if (arg is not MapElementHandlerUpdate args)
	return;
	handler.UpdateMapElement(args.MapElement);

maui/src/Core/maps/src/Handlers/Map/MapHandler.Android.cs

Lines 47 to 338 in ab2c30a

	protected override void ConnectHandler(MapView platformView)
	{
	base.ConnectHandler(platformView);
	_mapReady = new MapCallbackHandler(this);
	platformView.GetMapAsync(_mapReady);
	platformView.LayoutChange += MapViewLayoutChange;
	}
	protected override void DisconnectHandler(MapView platformView)
	{
	base.DisconnectHandler(platformView);
	platformView.LayoutChange -= MapViewLayoutChange;
	if (Map != null)
	{
	Map.SetOnCameraMoveListener(null);
	Map.MarkerClick -= OnMarkerClick;
	Map.InfoWindowClick -= OnInfoWindowClick;
	Map.MapClick -= OnMapClick;
	}
	_mapReady = null;
	}
	protected override MapView CreatePlatformView()
	{
	MapView mapView = new MapView(Context);
	mapView.OnCreate(s_bundle);
	mapView.OnResume();
	return mapView;
	}
	public static void MapMapType(IMapHandler handler, IMap map)
	{
	GoogleMap? googleMap = handler?.Map;
	googleMap?.UpdateMapType(map);
	}
	public static void MapIsShowingUser(IMapHandler handler, IMap map)
	{
	GoogleMap? googleMap = handler?.Map;
	googleMap?.UpdateIsShowingUser(map, handler?.MauiContext);
	}
	public static void MapIsScrollEnabled(IMapHandler handler, IMap map)
	{
	GoogleMap? googleMap = handler?.Map;
	googleMap?.UpdateIsScrollEnabled(map);
	}
	public static void MapIsTrafficEnabled(IMapHandler handler, IMap map)
	{
	GoogleMap? googleMap = handler?.Map;
	googleMap?.UpdateIsTrafficEnabled(map);
	}
	public static void MapIsZoomEnabled(IMapHandler handler, IMap map)
	{
	GoogleMap? googleMap = handler?.Map;
	googleMap?.UpdateIsZoomEnabled(map);
	}
	public static void MapMoveToRegion(IMapHandler handler, IMap map, object? arg)
	{
	MapSpan? newRegion = arg as MapSpan;
	if (newRegion != null)
	(handler as MapHandler)?.MoveToRegion(newRegion, true);
	}
	public void UpdateMapElement(IMapElement element)
	{
	switch (element)
	{
	case IGeoPathMapElement polyline:
	{
	if (element is IFilledMapElement polygon)
	{
	PolygonOnPropertyChanged(polyline);
	}
	else
	{
	PolylineOnPropertyChanged(polyline);
	}
	break;
	}
	case ICircleMapElement circle:
	{
	CircleOnPropertyChanged(circle);
	break;
	}
	}
	}
	void PolygonOnPropertyChanged(IGeoPathMapElement mauiPolygon)
	{
	var nativePolygon = GetNativePolygon(mauiPolygon);
	if (nativePolygon == null)
	return;
	if (mauiPolygon.Stroke is SolidPaint solidPaint)
	nativePolygon.StrokeColor = solidPaint.Color.AsColor();
	if ((mauiPolygon as IFilledMapElement)?.Fill is SolidPaint solidFillPaint)
	nativePolygon.FillColor = solidFillPaint.Color.AsColor();
	nativePolygon.StrokeWidth = (float)mauiPolygon.StrokeThickness;
	nativePolygon.Points = mauiPolygon.Select(position => new LatLng(position.Latitude, position.Longitude)).ToList();
	}
	void PolylineOnPropertyChanged(IGeoPathMapElement mauiPolyline)
	{
	var nativePolyline = GetNativePolyline(mauiPolyline);
	if (nativePolyline == null)
	return;
	if (mauiPolyline.Stroke is SolidPaint solidPaint)
	nativePolyline.Color = solidPaint.Color.AsColor();
	nativePolyline.Width = (float)mauiPolyline.StrokeThickness;
	nativePolyline.Points = mauiPolyline.Select(position => new LatLng(position.Latitude, position.Longitude)).ToList();
	}
	void CircleOnPropertyChanged(ICircleMapElement mauiCircle)
	{
	var nativeCircle = GetNativeCircle(mauiCircle);
	if (nativeCircle == null)
	return;
	if (mauiCircle.Stroke is SolidPaint solidPaint)
	nativeCircle.FillColor = solidPaint.Color.AsColor();
	if (mauiCircle.Fill is SolidPaint solidFillPaint)
	nativeCircle.FillColor = solidFillPaint.Color.AsColor();
	nativeCircle.Center = new LatLng(mauiCircle.Center.Latitude, mauiCircle.Center.Longitude);
	nativeCircle.Radius = mauiCircle.Radius.Meters;
	nativeCircle.StrokeWidth = (float)mauiCircle.StrokeThickness;
	}
	protected APolyline? GetNativePolyline(IGeoPathMapElement polyline)
	{
	APolyline? targetPolyline = null;
	if (_polylines != null && polyline.MapElementId is string)
	{
	for (int i = 0; i < _polylines.Count; i++)
	{
	var native = _polylines[i];
	if (native.Id == (string)polyline.MapElementId)
	{
	targetPolyline = native;
	break;
	}
	}
	}
	return targetPolyline;
	}
	protected ACircle? GetNativeCircle(ICircleMapElement circle)
	{
	ACircle? targetCircle = null;
	if (_circles != null && circle.MapElementId is string)
	{
	for (int i = 0; i < _circles.Count; i++)
	{
	var native = _circles[i];
	if (native.Id == (string)circle.MapElementId)
	{
	targetCircle = native;
	break;
	}
	}
	}
	return targetCircle;
	}
	protected APolygon? GetNativePolygon(IGeoPathMapElement polygon)
	{
	APolygon? targetPolygon = null;
	if (_polygons != null && polygon.MapElementId is string)
	{
	for (int i = 0; i < _polygons.Count; i++)
	{
	var native = _polygons[i];
	if (native.Id == (string)polygon.MapElementId)
	{
	targetPolygon = native;
	break;
	}
	}
	}
	return targetPolygon;
	}
	public static void MapPins(IMapHandler handler, IMap map)
	{
	if (handler is MapHandler mapHandler)
	{
	if (mapHandler._markers != null)
	{
	for (int i = 0; i < mapHandler._markers.Count; i++)
	mapHandler._markers[i].Remove();
	mapHandler._markers = null;
	}
	mapHandler.AddPins((IList)map.Pins);
	}
	}
	public static void MapElements(IMapHandler handler, IMap map)
	{
	(handler as MapHandler)?.ClearMapElements();
	(handler as MapHandler)?.AddMapElements((IList)map.Elements);
	}
	internal void OnMapReady(GoogleMap map)
	{
	if (map == null)
	{
	return;
	}
	Map = map;
	map.SetOnCameraMoveListener(_mapReady);
	map.MarkerClick += OnMarkerClick;
	map.InfoWindowClick += OnInfoWindowClick;
	map.MapClick += OnMapClick;
	if (VirtualView != null)
	{
	map.UpdateMapType(VirtualView);
	map.UpdateIsShowingUser(VirtualView, MauiContext);
	map.UpdateIsScrollEnabled(VirtualView);
	map.UpdateIsTrafficEnabled(VirtualView);
	map.UpdateIsZoomEnabled(VirtualView);
	}
	InitialUpdate();
	}
	internal void UpdateVisibleRegion(LatLng pos)
	{
	if (Map == null)
	return;
	Projection projection = Map.Projection;
	int width = PlatformView.Width;
	int height = PlatformView.Height;
	LatLng ul = projection.FromScreenLocation(new global::Android.Graphics.Point(0, 0));
	LatLng ur = projection.FromScreenLocation(new global::Android.Graphics.Point(width, 0));
	LatLng ll = projection.FromScreenLocation(new global::Android.Graphics.Point(0, height));
	LatLng lr = projection.FromScreenLocation(new global::Android.Graphics.Point(width, height));
	double dlat = Math.Max(Math.Abs(ul.Latitude - lr.Latitude), Math.Abs(ur.Latitude - ll.Latitude));
	double dlong = Math.Max(Math.Abs(ul.Longitude - lr.Longitude), Math.Abs(ur.Longitude - ll.Longitude));
	VirtualView.VisibleRegion = new MapSpan(new Devices.Sensors.Location(pos.Latitude, pos.Longitude), dlat, dlong);
	}
	void MapViewLayoutChange(object? sender, Android.Views.View.LayoutChangeEventArgs e)
	{
	InitialUpdate();
	}
	void InitialUpdate()
	{
	if (Map == null)
	return;
	if (_init && _lastMoveToRegion != null)
	{
	MoveToRegion(_lastMoveToRegion, false);
	if (_pins != null)
	AddPins(_pins);
	if (_elements != null)
	AddMapElements(_elements);
	_init = false;
	}

maui/src/Controls/Maps/src/HandlerImpl/Map.Impl.cs

Lines 1 to 38 in ab2c30a

	using System.Collections.Generic;
	using System.Linq;
	using Microsoft.Maui.Devices.Sensors;
	using Microsoft.Maui.Maps;
	namespace Microsoft.Maui.Controls.Maps
	{
	public partial class Map : IMap, IEnumerable<IMapPin>
	{
	IList<IMapElement> IMap.Elements => _mapElements.Cast<IMapElement>().ToList();
	IList<IMapPin> IMap.Pins => _pins.Cast<IMapPin>().ToList();
	void IMap.Clicked(Location location) => MapClicked?.Invoke(this, new MapClickedEventArgs(location));
	MapSpan? IMap.VisibleRegion
	{
	get
	{
	return _visibleRegion;
	}
	set
	{
	SetVisibleRegion(value);
	}
	}
	/// <summary>
	/// Raised when the handler for this map control changed.
	/// </summary>
	protected override void OnHandlerChanged()
	{
	base.OnHandlerChanged();
	//The user specified on the ctor a MapSpan we now need the handler to move to that region
	Handler?.Invoke(nameof(IMap.MoveToRegion), _lastMoveToRegion);
	}

maui/src/Controls/Maps/src/Map.cs

Lines 1 to 34 in ab2c30a

	using System;
	using System.Collections;
	using System.Collections.Generic;
	using System.Collections.ObjectModel;
	using System.Collections.Specialized;
	using System.ComponentModel;
	using System.Linq;
	using Microsoft.Maui.Controls.Internals;
	using Microsoft.Maui.Maps;
	namespace Microsoft.Maui.Controls.Maps
	{
	/// <summary>
	/// The Map control is a cross-platform view for displaying and annotating maps.
	/// </summary>
	public partial class Map : View
	{
	/// <summary>Bindable property for <see cref="MapType"/>.</summary>
	public static readonly BindableProperty MapTypeProperty = BindableProperty.Create(nameof(MapType), typeof(MapType), typeof(Map), default(MapType));
	/// <summary>Bindable property for <see cref="IsShowingUser"/>.</summary>
	public static readonly BindableProperty IsShowingUserProperty = BindableProperty.Create(nameof(IsShowingUser), typeof(bool), typeof(Map), default(bool));
	/// <summary>Bindable property for <see cref="IsTrafficEnabled"/>.</summary>
	public static readonly BindableProperty IsTrafficEnabledProperty = BindableProperty.Create(nameof(IsTrafficEnabled), typeof(bool), typeof(Map), default(bool));
	/// <summary>Bindable property for <see cref="IsScrollEnabled"/>.</summary>
	public static readonly BindableProperty IsScrollEnabledProperty = BindableProperty.Create(nameof(IsScrollEnabled), typeof(bool), typeof(Map), true);
	/// <summary>Bindable property for <see cref="IsZoomEnabled"/>.</summary>
	public static readonly BindableProperty IsZoomEnabledProperty = BindableProperty.Create(nameof(IsZoomEnabled), typeof(bool), typeof(Map), true);
	/// <summary>Bindable property for <see cref="ItemsSource"/>.</summary>
	public static readonly BindableProperty ItemsSourceProperty = BindableProperty.Create(nameof(ItemsSource), typeof(IEnumerable), typeof(Map), default(IEnumerable),

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Step 2: ⌨️ Coding

• Modify src/Core/maps/src/Handlers/Map/MapHandler.Android.cs ! No changes made Edit

Modify src/Core/maps/src/Handlers/Map/MapHandler.Android.cs with contents:
• Inside the OnMapReady method, after setting up the camera move listener, add logic to update the VisibleRegion of the IMap instance whenever the camera moves.
• To achieve this, modify the existing camera move event handler or the SetOnCameraMoveListener callback to include a call to a new method that calculates and updates the VisibleRegion based on the current camera position.
• For calculating the new VisibleRegion, use the GoogleMap's Projection to get the visible region's bounds and then update the IMap's VisibleRegion property. This might involve converting GoogleMap's LatLngBounds to the IMap's MapSpan format.
• Ensure that the update to VisibleRegion is done on the UI thread to prevent any potential threading issues.

• Running GitHub Actions for src/Core/maps/src/Handlers/Map/MapHandler.Android.cs ✗ Edit

Check src/Core/maps/src/Handlers/Map/MapHandler.Android.cs with contents:

• Modify src/Core/maps/src/Handlers/Map/MapHandler.cs ✓ 3d956e2 Edit

Modify src/Core/maps/src/Handlers/Map/MapHandler.cs with contents:
• Add a protected or public method named UpdateVisibleRegion or similar, which takes no parameters and updates the IMap's VisibleRegion property. This method will be called from the Android-specific handler as described above.
• This method should be virtual to allow overriding in platform-specific handlers if necessary.

--- 
+++ 
@@ -56,3 +56,7 @@
 		}
 	}
 }
+        protected virtual void UpdateVisibleRegion()
+        {
+            // Implement platform-specific logic to update the IMap's VisibleRegion property.
+        }

• Running GitHub Actions for src/Core/maps/src/Handlers/Map/MapHandler.cs ✓ Edit

Check src/Core/maps/src/Handlers/Map/MapHandler.cs with contents:

Ran GitHub Actions for 3d956e23ba7263651916cb0f251959b7961abc50:

• Modify src/Controls/Maps/src/Map.cs ! No changes made Edit

Modify src/Controls/Maps/src/Map.cs with contents:
• Ensure that the Map class, which implements IMap, has logic to correctly handle updates to its VisibleRegion property. This might involve raising property changed notifications if the VisibleRegion is a bindable property.
• If the VisibleRegion property does not already support property changed notifications, modify it to do so, ensuring that UI elements bound to this property are correctly updated when it changes.

• Running GitHub Actions for src/Controls/Maps/src/Map.cs ✗ Edit

Check src/Controls/Maps/src/Map.cs with contents:

---

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