From 137bb5538dc8cb69db9769b607b6d0a62ace13ac Mon Sep 17 00:00:00 2001
From: Kevin Petit <kevin.petit@hacksis.dev>
Date: Wed, 16 Mar 2022 20:53:54 +0100
Subject: [PATCH] Ensure that the GestureDetector is disposed

---
 .../Android/SwipeAwareContainerRenderer.cs    | 120 ++++++++++++------
 1 file changed, 82 insertions(+), 38 deletions(-)

diff --git a/src/Calendar.Plugin/Android/SwipeAwareContainerRenderer.cs b/src/Calendar.Plugin/Android/SwipeAwareContainerRenderer.cs
index 2fd385d..e035c25 100644
--- a/src/Calendar.Plugin/Android/SwipeAwareContainerRenderer.cs
+++ b/src/Calendar.Plugin/Android/SwipeAwareContainerRenderer.cs
@@ -5,74 +5,118 @@
 using Xamarin.Plugin.Calendar.Controls;
 using Xamarin.Forms;
 using Xamarin.Forms.Platform.Android;
+using View = Xamarin.Forms.View;
 
 [assembly: ExportRenderer(typeof(SwipeAwareContainer), typeof(SwipeAwareContainerRenderer))]
 namespace Xamarin.Plugin.Calendar.Android
 {
-    internal class SwipeAwareContainerRenderer : ViewRenderer, GestureDetector.IOnGestureListener
+    internal class SwipeAwareContainerRenderer : ViewRenderer
     {
         private const int SwipeDistanceThreshold = 50;
         private const int SwipeVelocityThreshold = 20;
-        private readonly GestureDetector _gestureDetector;
+        private GestureDetector _gestureDetector;
+        private GestureDetector.IOnGestureListener _gestureListener;
+        private bool _isDisposed;
 
         public SwipeAwareContainerRenderer(Context context) : base(context)
         {
-            _gestureDetector = new GestureDetector(context, this);
+        }
+
+        protected override void OnElementChanged(ElementChangedEventArgs<View> e)
+        {
+            base.OnElementChanged(e);
+
+            if (e.OldElement != null)
+            {
+                DisposeGestureDetectorAndListener();
+            }
+
+            if (e.NewElement != null)
+            {
+                _gestureListener = new InnerGestureListener(Element as SwipeAwareContainer);
+                _gestureDetector = new GestureDetector(Context, _gestureListener);
+            }
         }
 
         public override bool OnInterceptTouchEvent(MotionEvent ev)
         {
+            if (_isDisposed)
+                return false;
+
             if (Element is SwipeAwareContainer element && !element.SwipeDetectionDisabled)
-                _gestureDetector.OnTouchEvent(ev);
+                _gestureDetector?.OnTouchEvent(ev);
 
             return base.OnInterceptTouchEvent(ev);
         }
 
-        public bool OnFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)
+        protected override void Dispose(bool disposing)
         {
-            if (!(Element is SwipeAwareContainer element))
-                return false;
+            if (_isDisposed)
+                return;
 
-            float distanceX = e2.GetX() - e1.GetX();
-            float distanceY = e2.GetY() - e1.GetY();
+            _isDisposed = true;
 
-            if (Math.Abs(distanceX) > Math.Abs(distanceY))
+            if (disposing)
             {
-                if (Math.Abs(distanceX) > SwipeDistanceThreshold && Math.Abs(velocityX) > SwipeVelocityThreshold)
-                {
-                    if (distanceX > 0)
-                        element.OnSwipeRight();
-                    else
-                        element.OnSwipeLeft();
-
-                    return true;
-                }
+                DisposeGestureDetectorAndListener();
             }
-            else
-            {
-                if (Math.Abs(distanceY) > SwipeDistanceThreshold && Math.Abs(velocityY) > SwipeVelocityThreshold)
-                {
-                    if (distanceY > 0)
-                        element.OnSwipeDown();
-                    else
-                        element.OnSwipeUp();
 
-                    return true;
-                }
-            }
+            base.Dispose(disposing);
+        }
+
+        private void DisposeGestureDetectorAndListener()
+        {
+            _gestureDetector?.Dispose();
+            _gestureDetector = null;
 
-            return false;
+            _gestureListener?.Dispose();
+            _gestureListener = null;
         }
 
-        #region Unused gestures
+        private class InnerGestureListener : GestureDetector.SimpleOnGestureListener
+        {
+            private SwipeAwareContainer SwipeAwareContainer { get; }
+
+            public InnerGestureListener(SwipeAwareContainer swipeAwareContainer)
+            {
+                SwipeAwareContainer = swipeAwareContainer;
+            }
+
+            public override bool OnFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)
+            {
+                if (SwipeAwareContainer == null)
+                    return false;
+
+                float distanceX = e2.GetX() - e1.GetX();
+                float distanceY = e2.GetY() - e1.GetY();
 
-        public bool OnDown(MotionEvent e) => false;
-        public void OnLongPress(MotionEvent e) { }
-        public bool OnScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) => false;
-        public void OnShowPress(MotionEvent e) { }
-        public bool OnSingleTapUp(MotionEvent e) => false;
+                if (Math.Abs(distanceX) > Math.Abs(distanceY))
+                {
+                    if (Math.Abs(distanceX) > SwipeDistanceThreshold && Math.Abs(velocityX) > SwipeVelocityThreshold)
+                    {
+                        if (distanceX > 0)
+                            SwipeAwareContainer.OnSwipeRight();
+                        else
+                            SwipeAwareContainer.OnSwipeLeft();
 
-        #endregion
+                        return true;
+                    }
+                }
+                else
+                {
+                    if (Math.Abs(distanceY) > SwipeDistanceThreshold && Math.Abs(velocityY) > SwipeVelocityThreshold)
+                    {
+                        if (distanceY > 0)
+                            SwipeAwareContainer.OnSwipeDown();
+                        else
+                            SwipeAwareContainer.OnSwipeUp();
 
+                        return true;
+                    }
+                }
+
+                return false;
+            }
+        }
     }
 }
\ No newline at end of file