PlatformTouchEffect.cs

using CoreGraphics;
using Foundation;
using Microsoft.Maui.Controls.Platform;
using OxyPlot.Maui.Skia.Effects;
using UIKit;

namespace OxyPlot.Maui.Skia.ios.Effects;

public class PlatformTouchEffect : PlatformEffect
{
    UIView view;
    TouchRecognizer touchRecognizer;

    protected override void OnAttached()
    {
        // Get the iOS UIView corresponding to the Element that the effect is attached to
        view = Control ?? Container;

        // Uncomment this line if the UIView does not have touch enabled by default
        //view.UserInteractionEnabled = true;

        // Get access to the TouchEffect class in the .NET Standard library
        var touchEffect = Element.Effects.OfType<MyTouchEffect>().FirstOrDefault();

        if (touchEffect != null && view != null)
        {
            // Create a TouchRecognizer for this UIView
            touchRecognizer = new TouchRecognizer(Element, view, touchEffect);
            view.AddGestureRecognizer(touchRecognizer);
        }
    }

    protected override void OnDetached()
    {
        if (touchRecognizer != null)
        {
            // Clean up the TouchRecognizer object
            touchRecognizer.Detach();

            // Remove the TouchRecognizer from the UIView
            view.RemoveGestureRecognizer(touchRecognizer);
        }
    }
}

class TouchRecognizer : UIGestureRecognizer
{
    Microsoft.Maui.Controls.Element element;        // Forms element for firing events
    UIView view;            // iOS UIView 
    MyTouchEffect touchPlatformEffect;

    static Dictionary<UIView, TouchRecognizer> viewDictionary = new();

    static Dictionary<long, TouchRecognizer> idToTouchDictionary = new();

    public TouchRecognizer(Microsoft.Maui.Controls.Element element, UIView view, MyTouchEffect touchPlatformEffect)
    {
        this.element = element;
        this.view = view;
        this.touchPlatformEffect = touchPlatformEffect;

        viewDictionary.Add(view, this);
    }

    public void Detach()
    {
        viewDictionary.Remove(view);
    }

    // touches = touches of interest; evt = all touches of type UITouch
    public override void TouchesBegan(NSSet touches, UIEvent evt)
    {
        base.TouchesBegan(touches, evt);

        foreach (UITouch touch in touches.Cast<UITouch>())
        {
            long id = ((IntPtr)touch.Handle).ToInt64();
            FireEvent(this, id, TouchActionType.Pressed, touch, true);

            if (!idToTouchDictionary.ContainsKey(id))
            {
                idToTouchDictionary.Add(id, this);
            }
        }
    }

    public override void TouchesMoved(NSSet touches, UIEvent evt)
    {
        base.TouchesMoved(touches, evt);

        foreach (UITouch touch in touches.Cast<UITouch>())
        {
            long id = ((IntPtr)touch.Handle).ToInt64();
            CheckForBoundaryHop(touch);
            if (idToTouchDictionary[id] != null)
            {
                FireEvent(idToTouchDictionary[id], id, TouchActionType.Moved, touch, true);
            }
        }
    }

    public override void TouchesEnded(NSSet touches, UIEvent evt)
    {
        base.TouchesEnded(touches, evt);

        foreach (UITouch touch in touches.Cast<UITouch>())
        {
            long id = ((IntPtr)touch.Handle).ToInt64();
            CheckForBoundaryHop(touch);
            if (idToTouchDictionary[id] != null)
            {
                FireEvent(idToTouchDictionary[id], id, TouchActionType.Released, touch, false);
            }

            idToTouchDictionary.Remove(id);
        }
    }

    public override void TouchesCancelled(NSSet touches, UIEvent evt)
    {
        base.TouchesCancelled(touches, evt);

        foreach (UITouch touch in touches.Cast<UITouch>())
        {
            long id = ((IntPtr)touch.Handle).ToInt64();
            idToTouchDictionary.Remove(id);
        }
    }

    void CheckForBoundaryHop(UITouch touch)
    {
        long id = ((IntPtr)touch.Handle).ToInt64();

        // TODO: Might require converting to a List for multiple hits
        TouchRecognizer recognizerHit = null;

        foreach (UIView view in viewDictionary.Keys)
        {
            CGPoint location = touch.LocationInView(view);

            if (new CGRect(new CGPoint(), view.Frame.Size).Contains(location))
            {
                recognizerHit = viewDictionary[view];
            }
        }
        if (recognizerHit != idToTouchDictionary[id])
        {
            if (idToTouchDictionary[id] != null)
            {
                FireEvent(idToTouchDictionary[id], id, TouchActionType.Pressed, touch, true);
            }
            if (recognizerHit != null)
            {
                FireEvent(recognizerHit, id, TouchActionType.Released, touch, true);
            }
            idToTouchDictionary[id] = recognizerHit;
        }
    }

    void FireEvent(TouchRecognizer recognizer, long id, TouchActionType actionType, UITouch touch, bool isInContact)
    {
        // Convert touch location to Maui Point value
        CGPoint cgPoint = touch.LocationInView(recognizer.View);
        Point xfPoint = new Point(cgPoint.X, cgPoint.Y);

        // Get the method to call for firing events
        var onTouchAction = recognizer.touchPlatformEffect.OnTouchAction;

        // Call that method
        onTouchAction(recognizer.element,
            new TouchActionEventArgs(id, actionType, new[] { xfPoint }, isInContact));
    }
}