made sure to dispose properly for both platforms (#325)

Author: haavamoa

src/DIPS.Xamarin.UI.Android/ContextMenu/ContextMenuButtonRenderer.cs

@@ -37,24 +37,26 @@ protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
         {
             base.OnElementChanged(e);
 
-            if (e.NewElement is ContextMenuButton contextMenuButton)
+            if (e.NewElement is ContextMenuButton m_contextMenuButton)
             {
-                m_contextMenuButton = contextMenuButton;
+                m_contextMenuButton = m_contextMenuButton;
                 if (Control != null)
                 {
                     {
-                        contextMenuButton.Clicked += OpenContextMenu;
+                        m_contextMenuButton.Clicked += OpenContextMenu;
                         (((Activity)Context!)).RegisterActivityLifecycleCallbacks(this);
                     }
                 }
-                else
-                {
-                    contextMenuButton.Clicked -= OpenContextMenu;
-                    (((Activity)Context!)).UnregisterActivityLifecycleCallbacks(this);
-                }
             }
         }
 
+        protected override void Dispose(bool disposing)
+        {
+            m_contextMenuButton.Clicked -= OpenContextMenu;
+            (((Activity)Context!)).UnregisterActivityLifecycleCallbacks(this);
+            base.Dispose(disposing);
+        }
+
         private void OpenContextMenu(object sender, EventArgs e)
         {
             var gravity = (m_contextMenuButton.ContextMenuHorizontalOptions == ContextMenuHorizontalOptions.Right)

src/DIPS.Xamarin.UI.iOS/ContextMenu/ContextMenuButtonRenderer.cs

@@ -19,6 +19,7 @@ namespace DIPS.Xamarin.UI.iOS.ContextMenu
     internal class ContextMenuButtonRenderer : ButtonRenderer
     {
         private ContextMenuButton m_contextMenuButton;
+        private NSObject m_didEnterBackgroundNotificationObserver;
         internal static void Initialize() { }
 
         protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
@@ -36,22 +37,21 @@ protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
                             CreateMenu(); //Create the menu the first time so it shows up the first time the user taps the button
                         Control.TouchDown += OnTouchDown;
                         Control.ShowsMenuAsPrimaryAction = true;
-                        NSNotificationCenter.DefaultCenter.AddObserver(UIApplication.DidEnterBackgroundNotification, notification =>
+                        m_didEnterBackgroundNotificationObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIApplication.DidEnterBackgroundNotification, notification =>
                         {
                             Control.Menu = null;
                             Control.Menu = CreateMenu(); //Recreate the menu to close it, and to make it possible to re-open it in one tap after it went to the background
                         });
                     }
                 }
             }
-            else
-            {
-                if (Control != null)
-                {
-                    Control.TouchDown -= OnTouchDown;
-                    NSNotificationCenter.DefaultCenter.RemoveObserver(UIApplication.DidEnterBackgroundNotification);
-                }
-            }
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+            Control.TouchDown -= OnTouchDown;
+            NSNotificationCenter.DefaultCenter.RemoveObserver(m_didEnterBackgroundNotificationObserver);
+            base.Dispose(disposing);
         }
 
         private void OnTouchDown(object sender, EventArgs e)