Clear event handler only if it's the current event handler value

Previously, when an event handler was reset it would unconditionally clear the event. Instead, it should check if the value that is attempted to be clear is actually the current value. If not (say, because it's stale), it's ignored. If it is, it's cleared.

Fixes #80

src/BlinForms.Framework/Controls/Button.cs

@@ -59,7 +59,7 @@ public void ApplyAttribute(ulong attributeEventHandlerId, string attributeName,
                         Text = (string)attributeValue;
                         break;
                     case "onclick":
-                        Renderer.RegisterEvent(attributeEventHandlerId, () => ClickEventHandlerId = 0);
+                        Renderer.RegisterEvent(attributeEventHandlerId, id => { if (ClickEventHandlerId == id) ClickEventHandlerId = 0; });
                         ClickEventHandlerId = attributeEventHandlerId;
                         break;
                     default:

src/BlinForms.Framework/Controls/CheckBox.cs

@@ -102,11 +102,11 @@ public void ApplyAttribute(ulong attributeEventHandlerId, string attributeName,
                         ThreeState = AttributeHelper.GetBool(attributeValue);
                         break;
                     case "oncheckedchanged":
-                        Renderer.RegisterEvent(attributeEventHandlerId, () => CheckedChangedEventHandlerId = 0);
+                        Renderer.RegisterEvent(attributeEventHandlerId, id => { if (CheckedChangedEventHandlerId == id) CheckedChangedEventHandlerId = 0; });
                         CheckedChangedEventHandlerId = attributeEventHandlerId;
                         break;
                     case "oncheckstatechanged":
-                        Renderer.RegisterEvent(attributeEventHandlerId, () => CheckStateChangedEventHandlerId = 0);
+                        Renderer.RegisterEvent(attributeEventHandlerId, id => { if (CheckStateChangedEventHandlerId == id) CheckStateChangedEventHandlerId = 0; });
                         CheckStateChangedEventHandlerId = attributeEventHandlerId;
                         break;
                     default:

src/BlinForms.Framework/Controls/TextBox.cs

@@ -96,7 +96,7 @@ public void ApplyAttribute(ulong attributeEventHandlerId, string attributeName,
                         ScrollBars = (ScrollBars)AttributeHelper.GetInt(attributeValue);
                         break;
                     case "ontextchanged":
-                        Renderer.RegisterEvent(attributeEventHandlerId, () => TextChangedEventHandlerId = 0);
+                        Renderer.RegisterEvent(attributeEventHandlerId, id => { if (TextChangedEventHandlerId == id) TextChangedEventHandlerId = 0; });
                         TextChangedEventHandlerId = attributeEventHandlerId;
                         break;
                     default:

src/Microsoft.MobileBlazorBindings.Core/NativeComponentRenderer.cs

@@ -15,7 +15,7 @@ public abstract class NativeComponentRenderer : Renderer
     {
         private readonly Dictionary<int, NativeComponentAdapter> _componentIdToAdapter = new Dictionary<int, NativeComponentAdapter>();
         private ElementManager _elementManager;
-        private readonly Dictionary<ulong, Action> _eventRegistrations = new Dictionary<ulong, Action>();
+        private readonly Dictionary<ulong, Action<ulong>> _eventRegistrations = new Dictionary<ulong, Action<ulong>>();
 
 
         public NativeComponentRenderer(IServiceProvider serviceProvider, ILoggerFactory loggerFactory)
@@ -102,7 +102,7 @@ protected override Task UpdateDisplayAsync(in RenderBatch renderBatch)
             return Task.CompletedTask;
         }
 
-        public void RegisterEvent(ulong eventHandlerId, Action unregisterCallback)
+        public void RegisterEvent(ulong eventHandlerId, Action<ulong> unregisterCallback)
         {
             if (eventHandlerId == 0)
             {
@@ -121,7 +121,7 @@ private void DisposeEvent(ulong eventHandlerId)
             {
                 throw new InvalidOperationException($"Attempting to dispose unknown event handler id '{eventHandlerId}'.");
             }
-            unregisterCallback();
+            unregisterCallback(eventHandlerId);
         }
 
         internal NativeComponentAdapter CreateAdapterForChildComponent(IElementHandler physicalParent, int componentId)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/BaseShellItemHandler.cs

@@ -12,7 +12,7 @@ public partial class BaseShellItemHandler : NavigableElementHandler
             RegisterEvent(
                 eventName: "onappearing",
                 setId: id => AppearingEventHandlerId = id,
-                clearId: () => AppearingEventHandlerId = 0);
+                clearId: id => { if (AppearingEventHandlerId == id) AppearingEventHandlerId = 0; });
             BaseShellItemControl.Appearing += (s, e) =>
             {
                 if (AppearingEventHandlerId != default)
@@ -23,7 +23,7 @@ public partial class BaseShellItemHandler : NavigableElementHandler
             RegisterEvent(
                 eventName: "ondisappearing",
                 setId: id => DisappearingEventHandlerId = id,
-                clearId: () => DisappearingEventHandlerId = 0);
+                clearId: id => { if (DisappearingEventHandlerId == id) DisappearingEventHandlerId = 0; });
             BaseShellItemControl.Disappearing += (s, e) =>
             {
                 if (DisappearingEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/ButtonHandler.cs

@@ -12,7 +12,7 @@ public partial class ButtonHandler : ViewHandler
             RegisterEvent(
                 eventName: "onclick",
                 setId: id => ClickEventHandlerId = id,
-                clearId: () => ClickEventHandlerId = 0);
+                clearId: id => { if (ClickEventHandlerId == id) ClickEventHandlerId = 0; });
             ButtonControl.Clicked += (s, e) =>
             {
                 if (ClickEventHandlerId != default)
@@ -24,7 +24,7 @@ public partial class ButtonHandler : ViewHandler
             RegisterEvent(
                 eventName: "onpress",
                 setId: id => PressEventHandlerId = id,
-                clearId: () => PressEventHandlerId = 0);
+                clearId: id => { if (PressEventHandlerId == id) PressEventHandlerId = 0; });
             ButtonControl.Pressed += (s, e) =>
             {
                 if (PressEventHandlerId != default)
@@ -36,7 +36,7 @@ public partial class ButtonHandler : ViewHandler
             RegisterEvent(
                 eventName: "onrelease",
                 setId: id => ReleaseEventHandlerId = id,
-                clearId: () => ReleaseEventHandlerId = 0);
+                clearId: id => { if (ReleaseEventHandlerId == id) ReleaseEventHandlerId = 0; });
             ButtonControl.Released += (s, e) =>
             {
                 if (ReleaseEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/CheckBoxHandler.cs

@@ -13,7 +13,7 @@ public partial class CheckBoxHandler : ViewHandler
             RegisterEvent(
                 eventName: "onischeckedchanged",
                 setId: id => IsCheckedChangedEventHandlerId = id,
-                clearId: () => IsCheckedChangedEventHandlerId = 0);
+                clearId: id => { if (IsCheckedChangedEventHandlerId == id) IsCheckedChangedEventHandlerId = 0; });
             CheckBoxControl.CheckedChanged += (s, e) =>
             {
                 if (IsCheckedChangedEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/ElementHandler.cs

@@ -16,7 +16,7 @@ public ElementHandler(NativeComponentRenderer renderer, XF.Element elementContro
             ElementControl = elementControl ?? throw new ArgumentNullException(nameof(elementControl));
         }
 
-        protected void RegisterEvent(string eventName, Action<ulong> setId, Action clearId)
+        protected void RegisterEvent(string eventName, Action<ulong> setId, Action<ulong> clearId)
         {
             RegisteredEvents[eventName] = new EventRegistration(eventName, setId, clearId);
         }

src/Microsoft.MobileBlazorBindings/Elements/Handlers/EntryHandler.cs

@@ -13,7 +13,7 @@ public partial class EntryHandler : InputViewHandler
             RegisterEvent(
                 eventName: "oncompleted",
                 setId: id => CompletedEventHandlerId = id,
-                clearId: () => CompletedEventHandlerId = 0);
+                clearId: id => { if (CompletedEventHandlerId == id) CompletedEventHandlerId = 0; });
             EntryControl.Completed += (s, e) =>
             {
                 if (CompletedEventHandlerId != default)
@@ -24,7 +24,7 @@ public partial class EntryHandler : InputViewHandler
             RegisterEvent(
                 eventName: "ontextchanged",
                 setId: id => TextChangedEventHandlerId = id,
-                clearId: () => TextChangedEventHandlerId = 0);
+                clearId: id => { if (TextChangedEventHandlerId == id) TextChangedEventHandlerId = 0; });
             EntryControl.TextChanged += (s, e) =>
             {
                 if (TextChangedEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/EventRegistration.cs

@@ -7,7 +7,7 @@ namespace Microsoft.MobileBlazorBindings.Elements.Handlers
 {
     internal class EventRegistration
     {
-        public EventRegistration(string eventName, Action<ulong> setId, Action clearId)
+        public EventRegistration(string eventName, Action<ulong> setId, Action<ulong> clearId)
         {
             if (string.IsNullOrEmpty(eventName))
             {
@@ -21,6 +21,6 @@ public EventRegistration(string eventName, Action<ulong> setId, Action clearId)
 
         public string EventName { get; }
         public Action<ulong> SetId { get; }
-        public Action ClearId { get; }
+        public Action<ulong> ClearId { get; }
     }
 }

src/Microsoft.MobileBlazorBindings/Elements/Handlers/ImageButtonHandler.cs

@@ -12,7 +12,7 @@ public partial class ImageButtonHandler : ViewHandler
             RegisterEvent(
                 eventName: "onclick",
                 setId: id => ClickEventHandlerId = id,
-                clearId: () => ClickEventHandlerId = 0);
+                clearId: id => { if (ClickEventHandlerId == id) ClickEventHandlerId = 0; });
             ImageButtonControl.Clicked += (s, e) =>
             {
                 if (ClickEventHandlerId != default)
@@ -24,7 +24,7 @@ public partial class ImageButtonHandler : ViewHandler
             RegisterEvent(
                 eventName: "onpress",
                 setId: id => PressEventHandlerId = id,
-                clearId: () => PressEventHandlerId = 0);
+                clearId: id => { if (PressEventHandlerId == id) PressEventHandlerId = 0; });
             ImageButtonControl.Pressed += (s, e) =>
             {
                 if (PressEventHandlerId != default)
@@ -36,7 +36,7 @@ public partial class ImageButtonHandler : ViewHandler
             RegisterEvent(
                 eventName: "onrelease",
                 setId: id => ReleaseEventHandlerId = id,
-                clearId: () => ReleaseEventHandlerId = 0);
+                clearId: id => { if (ReleaseEventHandlerId == id) ReleaseEventHandlerId = 0; });
             ImageButtonControl.Released += (s, e) =>
             {
                 if (ReleaseEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/MenuItemHandler.cs

@@ -12,7 +12,7 @@ public partial class MenuItemHandler : BaseMenuItemHandler
             RegisterEvent(
                 eventName: "onclick",
                 setId: id => ClickEventHandlerId = id,
-                clearId: () => ClickEventHandlerId = 0);
+                clearId: id => { if (ClickEventHandlerId == id) ClickEventHandlerId = 0; });
             MenuItemControl.Clicked += (s, e) =>
             {
                 if (ClickEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/ModalContainerHandler.cs

@@ -59,7 +59,7 @@ public void ApplyAttribute(ulong attributeEventHandlerId, string attributeName,
                     }
                     break;
                 case "onclosed":
-                    Renderer.RegisterEvent(attributeEventHandlerId, () => ClosedEventHandlerId = 0);
+                    Renderer.RegisterEvent(attributeEventHandlerId, id => { if (ClosedEventHandlerId == id) ClosedEventHandlerId = 0; });
                     ClosedEventHandlerId = attributeEventHandlerId;
                     break;
                 default:

src/Microsoft.MobileBlazorBindings/Elements/Handlers/ShellHandler.cs

@@ -26,7 +26,7 @@ public partial class ShellHandler : PageHandler
             RegisterEvent(
                 eventName: "onnavigated",
                 setId: id => NavigatedEventHandlerId = id,
-                clearId: () => NavigatedEventHandlerId = 0);
+                clearId: id => { if (NavigatedEventHandlerId == id) NavigatedEventHandlerId = 0; });
             ShellControl.Navigated += (s, e) =>
             {
                 if (NavigatedEventHandlerId != default)
@@ -37,7 +37,7 @@ public partial class ShellHandler : PageHandler
             RegisterEvent(
                 eventName: "onnavigating",
                 setId: id => NavigatingEventHandlerId = id,
-                clearId: () => NavigatingEventHandlerId = 0);
+                clearId: id => { if (NavigatingEventHandlerId == id) NavigatingEventHandlerId = 0; });
             ShellControl.Navigating += (s, e) =>
             {
                 if (NavigatingEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/SliderHandler.cs

@@ -13,7 +13,7 @@ public partial class SliderHandler : ViewHandler
             RegisterEvent(
                 eventName: "ondragcompleted",
                 setId: id => DragCompletedEventHandlerId = id,
-                clearId: () => DragCompletedEventHandlerId = 0);
+                clearId: id => { if (DragCompletedEventHandlerId == id) DragCompletedEventHandlerId = 0; });
             SliderControl.DragCompleted += (s, e) =>
             {
                 if (DragCompletedEventHandlerId != default)
@@ -25,7 +25,7 @@ public partial class SliderHandler : ViewHandler
             RegisterEvent(
                 eventName: "ondragstarted",
                 setId: id => DragStartedEventHandlerId = id,
-                clearId: () => DragStartedEventHandlerId = 0);
+                clearId: id => { if (DragStartedEventHandlerId == id) DragStartedEventHandlerId = 0; });
             SliderControl.DragStarted += (s, e) =>
             {
                 if (DragStartedEventHandlerId != default)
@@ -37,7 +37,7 @@ public partial class SliderHandler : ViewHandler
             RegisterEvent(
                 eventName: "onvaluechanged",
                 setId: id => ValueChangedEventHandlerId = id,
-                clearId: () => ValueChangedEventHandlerId = 0);
+                clearId: id => { if (ValueChangedEventHandlerId == id) ValueChangedEventHandlerId = 0; });
             SliderControl.ValueChanged += (s, e) =>
             {
                 if (ValueChangedEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/StepperHandler.cs

@@ -13,7 +13,7 @@ public partial class StepperHandler : ViewHandler
             RegisterEvent(
                 eventName: "onvaluechanged",
                 setId: id => ValueChangedEventHandlerId = id,
-                clearId: () => ValueChangedEventHandlerId = 0);
+                clearId: id => { if (ValueChangedEventHandlerId == id) ValueChangedEventHandlerId = 0; });
             StepperControl.ValueChanged += (s, e) =>
             {
                 if (ValueChangedEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/SwitchHandler.cs

@@ -13,7 +13,7 @@ public partial class SwitchHandler : ViewHandler
             RegisterEvent(
                 eventName: "onistoggledchanged",
                 setId: id => IsToggledChangedEventHandlerId = id,
-                clearId: () => IsToggledChangedEventHandlerId = 0);
+                clearId: id => { if (IsToggledChangedEventHandlerId == id) IsToggledChangedEventHandlerId = 0; });
             SwitchControl.Toggled += (s, e) =>
             {
                 if (IsToggledChangedEventHandlerId != default)

src/Microsoft.MobileBlazorBindings/Elements/Handlers/VisualElementHandler.cs

@@ -12,7 +12,7 @@ public partial class VisualElementHandler : NavigableElementHandler
             RegisterEvent(
                 eventName: "onfocused",
                 setId: id => FocusedEventHandlerId = id,
-                clearId: () => FocusedEventHandlerId = 0);
+                clearId: id => { if (FocusedEventHandlerId == id) FocusedEventHandlerId = 0; });
             VisualElementControl.Focused += (s, e) =>
             {
                 if (FocusedEventHandlerId != default)
@@ -23,7 +23,7 @@ public partial class VisualElementHandler : NavigableElementHandler
             RegisterEvent(
                 eventName: "onsizechanged",
                 setId: id => SizeChangedEventHandlerId = id,
-                clearId: () => SizeChangedEventHandlerId = 0);
+                clearId: id => { if (SizeChangedEventHandlerId == id) SizeChangedEventHandlerId = 0; });
             VisualElementControl.SizeChanged += (s, e) =>
             {
                 if (SizeChangedEventHandlerId != default)
@@ -34,7 +34,7 @@ public partial class VisualElementHandler : NavigableElementHandler
             RegisterEvent(
                 eventName: "onunfocused",
                 setId: id => UnfocusedEventHandlerId = id,
-                clearId: () => UnfocusedEventHandlerId = 0);
+                clearId: id => { if (UnfocusedEventHandlerId == id) UnfocusedEventHandlerId = 0; });
             VisualElementControl.Unfocused += (s, e) =>
             {
                 if (UnfocusedEventHandlerId != default)