From 379d43d553b3578e4424df93600d9c395ae2e4e2 Mon Sep 17 00:00:00 2001
From: TheXamlGuy <dan_clark@outlook.com>
Date: Sun, 29 Sep 2024 15:01:02 +0100
Subject: [PATCH] Added an EventListenerBehaviour for listening for events
 raised from the source

---
 .../AttachedEventTriggerBehaviour.cs          |   3 +-
 Toolkit.UI.Avalonia/EventListenerBehaviour.cs | 133 ++++++++++++++++++
 .../KeyBindingTriggerBehaviour.cs             |   9 --
 3 files changed, 135 insertions(+), 10 deletions(-)
 create mode 100644 Toolkit.UI.Avalonia/EventListenerBehaviour.cs

diff --git a/Toolkit.UI.Avalonia/AttachedEventTriggerBehaviour.cs b/Toolkit.UI.Avalonia/AttachedEventTriggerBehaviour.cs
index 25cb5fd..8c6526d 100644
--- a/Toolkit.UI.Avalonia/AttachedEventTriggerBehaviour.cs
+++ b/Toolkit.UI.Avalonia/AttachedEventTriggerBehaviour.cs
@@ -4,7 +4,8 @@ using Avalonia.Xaml.Interactivity;
 
 namespace Toolkit.UI.Avalonia;
 
-public class AttachedEventTriggerBehaviour : Trigger
+public class AttachedEventTriggerBehaviour :
+    Trigger
 {
     public static readonly StyledProperty<RoutedEvent> RoutedEventProperty =
         AvaloniaProperty.Register<AttachedEventTriggerBehaviour, RoutedEvent>(nameof(RoutedEvent));
diff --git a/Toolkit.UI.Avalonia/EventListenerBehaviour.cs b/Toolkit.UI.Avalonia/EventListenerBehaviour.cs
new file mode 100644
index 0000000..83ec6f7
--- /dev/null
+++ b/Toolkit.UI.Avalonia/EventListenerBehaviour.cs
@@ -0,0 +1,133 @@
+using Avalonia;
+using Avalonia.Xaml.Interactivity;
+using System.Reactive;
+using System.Reflection;
+
+namespace Toolkit.UI.Avalonia;
+
+public class EventListenerBehaviour :
+    Trigger
+{
+    public static readonly StyledProperty<string> EventNameProperty =
+        AvaloniaProperty.Register<EventListenerBehaviour, string>(nameof(EventName));
+
+    public static readonly StyledProperty<object> SourceProperty =
+        AvaloniaProperty.Register<EventListenerBehaviour, object>(nameof(Source));
+
+    private Delegate? eventHandler;
+    private object? resolvedSource;
+
+    static EventListenerBehaviour()
+    {
+        EventNameProperty.Changed.Subscribe(new AnonymousObserver<AvaloniaPropertyChangedEventArgs<string>>(EventNamePropertyChanged));
+        SourceProperty.Changed.Subscribe(new AnonymousObserver<AvaloniaPropertyChangedEventArgs<object>>(SourcePropertyChanged));
+    }
+
+    public string EventName
+    {
+        get => GetValue(EventNameProperty);
+        set => SetValue(EventNameProperty, value);
+    }
+
+    public object Source
+    {
+        get => GetValue(SourceProperty);
+        set => SetValue(SourceProperty, value);
+    }
+
+    private static void EventNamePropertyChanged(AvaloniaPropertyChangedEventArgs<string> args)
+    {
+        if (args.Sender is EventListenerBehaviour behaviour)
+        {
+            if (args.OldValue.GetValueOrDefault() is string oldValue)
+            {
+                behaviour.UnregisterEvent(oldValue);
+            }
+
+            if (args.NewValue.GetValueOrDefault() is string newValue)
+            {
+                behaviour.RegisterEvent(newValue);
+            }
+        }
+    }
+
+    private static void SourcePropertyChanged(AvaloniaPropertyChangedEventArgs<object> args)
+    {
+        if (args.Sender is EventListenerBehaviour behaviour)
+        {
+            behaviour.SetResolvedSource(args.GetNewValue<object>());
+        }
+    }
+
+
+    private void OnEventRaised(object? sender, EventArgs args)
+    {
+        if (IsEnabled)
+        {
+            Interaction.ExecuteActions(AssociatedObject, Actions, null);
+        }
+    }
+
+    private void RegisterEvent(string eventName)
+    {
+        if (eventName is { Length: 0 })
+        {
+            return;
+        }
+
+        if (resolvedSource is null)
+        {
+            return;
+        }
+
+        Type sourceType = resolvedSource.GetType();
+        if (sourceType.GetEvent(EventName) is EventInfo eventInfo)
+        {
+            eventInfo.AddEventHandler(resolvedSource, new EventHandler(OnEventRaised));
+        }
+    }
+
+    private void SetResolvedSource(object? newSource)
+    {
+        if (resolvedSource == newSource)
+        {
+            return;
+        }
+
+        if (resolvedSource is not null)
+        {
+            UnregisterEvent(EventName);
+        }
+
+        resolvedSource = newSource;
+
+        if (resolvedSource is not null)
+        {
+            RegisterEvent(EventName);
+        }
+    }
+
+    private void UnregisterEvent(string eventName)
+    {
+        if (eventHandler is null)
+        {
+            return;
+        }
+
+        if (eventName is { Length: 0 })
+        {
+            return;
+        }
+
+        if (resolvedSource is null)
+        {
+            return;
+        }
+
+        Type sourceType = resolvedSource.GetType();
+        if (sourceType.GetEvent(EventName) is EventInfo eventInfo)
+        {
+            eventInfo.RemoveEventHandler(resolvedSource, new EventHandler(OnEventRaised));
+        }
+    }
+}
diff --git a/Toolkit.UI.Avalonia/KeyBindingTriggerBehaviour.cs b/Toolkit.UI.Avalonia/KeyBindingTriggerBehaviour.cs
index 6d506f6..ef45513 100644
--- a/Toolkit.UI.Avalonia/KeyBindingTriggerBehaviour.cs
+++ b/Toolkit.UI.Avalonia/KeyBindingTriggerBehaviour.cs
@@ -12,21 +12,12 @@ public class KeyBindingTriggerBehaviour :
     public static readonly StyledProperty<KeyGesture> GestureProperty =
         AvaloniaProperty.Register<KeyBindingTriggerBehaviour, KeyGesture>(nameof(Gesture));
 
-    public static readonly StyledProperty<bool> IsEnabledProperty =
-        AvaloniaProperty.Register<KeyBindingTriggerBehaviour, bool>(nameof(IsEnabled), true);
-
     public KeyGesture Gesture
     {
         get => GetValue(GestureProperty);
         set => SetValue(GestureProperty, value);
     }
 
-    public bool IsEnabled
-    {
-        get => GetValue(IsEnabledProperty);
-        set => SetValue(IsEnabledProperty, value);
-    }
-
     public event EventHandler? CanExecuteChanged;
 
     protected override void OnAttached()