Fix an issue that ThemeHelper isn't enabled after reloading.

source/MetroRadiance/UI/Controls/ThemeHelper.cs

@@ -10,7 +10,10 @@ namespace MetroRadiance.UI.Controls
 	public static class ThemeHelper
 	{
 		private static readonly Dictionary<FrameworkElement, IDisposable> registeredElements = new Dictionary<FrameworkElement, IDisposable>();
-
+
+		private static void AddResources(FrameworkElement element)
+			=> registeredElements[element] = ThemeService.Current.Register(element.Resources);
+
 		private static void RemoveResources(FrameworkElement element)
 		{
 			IDisposable disposable;
@@ -58,8 +61,7 @@ private static void HasThemeResourcesChangedCallback(DependencyObject d, Depende
 				else if (!oldValue && newValue)
 				{
 					// false -> true
-					registeredElements[element] = ThemeService.Current.Register(element.Resources);
-					element.Unloaded += ElementUnloadedCallback;
+					FrameworkElementLoadedWeakEventManager.AddHandler(element, ElementLoadedCallback);
 				}
 			};
 
@@ -79,6 +81,13 @@ private static void HasThemeResourcesChangedCallback(DependencyObject d, Depende
 			}
 		}
 
+		private static void ElementLoadedCallback(object sender, RoutedEventArgs e)
+		{
+			var element = (FrameworkElement)sender;
+			AddResources(element);
+			element.Unloaded += ElementUnloadedCallback;
+		}
+
 		private static void ElementUnloadedCallback(object sender, RoutedEventArgs e)
 		{
 			var element = (FrameworkElement)sender;
@@ -87,5 +96,70 @@ private static void ElementUnloadedCallback(object sender, RoutedEventArgs e)
 		}
 
 		#endregion
+
+		private sealed class FrameworkElementLoadedWeakEventManager : WeakEventManager
+		{
+			/// <summary>
+			/// Add a handler for the given source's event.
+			/// </summary>
+			public static void AddHandler(FrameworkElement source, EventHandler<RoutedEventArgs> handler)
+			{
+				if (source == null) throw new ArgumentNullException(nameof(source));
+				if (handler == null) throw new ArgumentNullException(nameof(handler));
+
+				CurrentManager.ProtectedAddHandler(source, handler);
+			}
+
+			/// <summary>
+			/// Remove a handler for the given source's event.
+			/// </summary>
+			public static void RemoveHandler(FrameworkElement source, EventHandler<RoutedEventArgs> handler)
+			{
+				if (source == null) throw new ArgumentNullException(nameof(source));
+				if (handler == null) throw new ArgumentNullException(nameof(handler));
+
+				CurrentManager.ProtectedRemoveHandler(source, handler);
+			}
+
+			private static FrameworkElementLoadedWeakEventManager CurrentManager
+			{
+				get
+				{
+					var managerType = typeof(FrameworkElementLoadedWeakEventManager);
+					var manager = (FrameworkElementLoadedWeakEventManager)GetCurrentManager(managerType);
+					if (manager == null)
+					{
+						manager = new FrameworkElementLoadedWeakEventManager();
+						SetCurrentManager(managerType, manager);
+					}
+					return manager;
+				}
+			}
+
+			private FrameworkElementLoadedWeakEventManager()
+			{ }
+
+			protected override ListenerList NewListenerList()
+			{
+				return new ListenerList<RoutedEventArgs>();
+			}
+
+			protected override void StartListening(object source)
+			{
+				var element = (FrameworkElement)source;
+				element.Loaded += this.OnElementLoaded;
+			}
+
+			protected override void StopListening(object source)
+			{
+				var element = (FrameworkElement)source;
+				element.Loaded -= this.OnElementLoaded;
+			}
+
+			private void OnElementLoaded(object sender, RoutedEventArgs e)
+			{
+				this.DeliverEvent(sender, e);
+			}
+		}
 	}
 }