Refactor WeakReferenceList/CopyOnWriteList as type-safe generic collections

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/PresentationSource.cs

@@ -449,7 +449,7 @@ protected void RootChanged(Visual oldRoot, Visual newRoot)
             // To fire PresentationSourceChanged when the RootVisual changes;
             // rather than simulate a "parent" pointer change, we just walk the
             // collection of all nodes that need the event.
-            foreach (DependencyObject element in _watchers)
+            foreach (DependencyObject element in s_watchers)
             {
                 // We only need to update those elements that are in the
                 // same context as this presentation source.
@@ -475,15 +475,15 @@ protected void RootChanged(Visual oldRoot, Visual newRoot)
         /// </summary>
         protected void AddSource()
         {
-            _sources.Add(this);
+            s_sources.Add(this);
         }
 
         /// <summary>
         ///     Called by derived classes to indicate that they no longer need to be tracked.
         /// </summary>
         protected void RemoveSource()
         {
-            _sources.Remove(this);
+            s_sources.Remove(this);
         }
 
         /// <summary>
@@ -613,17 +613,14 @@ internal static bool IsUnderSamePresentationSource(params ReadOnlySpan<Dependenc
         ///   over a ReadOnly SnapShot of the List of sources.  The Enumerator
         ///   skips over the any dead weak references in the list.
         /// </summary>
-        internal static WeakReferenceList CriticalCurrentSources
+        internal static WeakReferenceList<PresentationSource> CriticalCurrentSources
         {
-            get
-            {
-                return _sources;
-            }
+            get => s_sources;
         }
 
         private static void AddElementToWatchList(DependencyObject element)
         {
-            if(_watchers.Add(element))
+            if (s_watchers.Add(element))
             {
                 element.SetValue(CachedSourceProperty, PresentationSource.FindSource(element));
                 element.SetValue(GetsSourceChangedEventProperty, true);
@@ -633,7 +630,7 @@ private static void AddElementToWatchList(DependencyObject element)
 
         private static void RemoveElementFromWatchList(DependencyObject element)
         {
-            if(_watchers.Remove(element))
+            if (s_watchers.Remove(element))
             {
                 element.ClearValue(CachedSourceProperty);
                 element.ClearValue(GetsSourceChangedEventProperty);
@@ -741,11 +738,11 @@ private static readonly DependencyProperty CachedSourceProperty
         private static readonly object _globalLock = new object();
 
         // An array of weak-references to sources that we know about.
-        private static WeakReferenceList _sources = new WeakReferenceList(_globalLock);
+        private static readonly WeakReferenceList<PresentationSource> s_sources = new(_globalLock);
 
         // An array of weak-references to elements that need to know
         // about source changes.
-        private static WeakReferenceList _watchers = new WeakReferenceList(_globalLock);
+        private static readonly WeakReferenceList<DependencyObject> s_watchers = new(_globalLock);
 
         #endregion
     }

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Diagnostics/ResourceDictionaryDiagnostics.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 //
@@ -51,7 +51,7 @@ public static IEnumerable<ResourceDictionaryInfo> ThemedResourceDictionaries
             {
                 if (!IsEnabled)
                 {
-                    return ResourceDictionaryDiagnostics.EmptyResourceDictionaryInfos;
+                    return ReadOnlyCollection<ResourceDictionaryInfo>.Empty;
                 }
 
                 return SystemResources.ThemedResourceDictionaries;
@@ -69,7 +69,7 @@ public static IEnumerable<ResourceDictionaryInfo> GenericResourceDictionaries
             {
                 if (!IsEnabled)
                 {
-                    return ResourceDictionaryDiagnostics.EmptyResourceDictionaryInfos;
+                    return ReadOnlyCollection<ResourceDictionaryInfo>.Empty;
                 }
 
                 return SystemResources.GenericResourceDictionaries;
@@ -276,47 +276,38 @@ private static IReadOnlyCollection<ResourceDictionary> EmptyResourceDictionaries
 
         public static IEnumerable<FrameworkElement> GetFrameworkElementOwners(ResourceDictionary dictionary)
         {
-            return GetOwners<FrameworkElement>(dictionary.FrameworkElementOwners, EmptyFrameworkElementList);
+            return GetOwners(dictionary.FrameworkElementOwners);
         }
 
         public static IEnumerable<FrameworkContentElement> GetFrameworkContentElementOwners(ResourceDictionary dictionary)
         {
-            return GetOwners<FrameworkContentElement>(dictionary.FrameworkContentElementOwners, EmptyFrameworkContentElementList);
+            return GetOwners(dictionary.FrameworkContentElementOwners);
         }
 
         public static IEnumerable<Application> GetApplicationOwners(ResourceDictionary dictionary)
         {
-            return GetOwners<Application>(dictionary.ApplicationOwners, EmptyApplicationList);
+            return GetOwners(dictionary.ApplicationOwners);
         }
 
-        private static IEnumerable<T> GetOwners<T>(WeakReferenceList list, IEnumerable<T> emptyList)
+        private static IEnumerable<T> GetOwners<T>(WeakReferenceList<T> list)
             where T : DispatcherObject
         {
             if (!IsEnabled || list == null || list.Count == 0)
             {
-                return emptyList;
+                return Array.Empty<T>();
             }
 
-            List<T> result = new List<T>(list.Count);
-            foreach (Object o in list)
+            // Copy list manually as it doesn't implement ICollection<T>
+            List<T> owners = new List<T>(list.Count);
+            foreach (T item in list)
             {
-                T owner = o as T;
-                if (owner != null)
-                {
-                    result.Add(owner);
-                }
+                owners.Add(item);
             }
 
-            return result.AsReadOnly();
+            // Create a read-only copy of the list
+            return owners.AsReadOnly();
         }
 
-        private static IReadOnlyCollection<FrameworkElement> EmptyFrameworkElementList
-            => Array.Empty<FrameworkElement>();
-        private static IReadOnlyCollection<FrameworkContentElement> EmptyFrameworkContentElementList
-            => Array.Empty<FrameworkContentElement>();
-        private static IReadOnlyCollection<Application> EmptyApplicationList
-            => Array.Empty<Application>();
-
         #endregion
 
         #region Notify when static resource references are resolved
@@ -548,7 +539,5 @@ internal class LookupResult
 
         internal static bool IsEnabled { get; private set; }
 
-        private static readonly ReadOnlyCollection<ResourceDictionaryInfo> EmptyResourceDictionaryInfos
-            = new List<ResourceDictionaryInfo>().AsReadOnly();
     }
 }