[Fix] Don't ignore application resource invalidations (#9527)

* [Fix] Don't ignore application resource invalidations

* Fix ignoring legitimate ResourceChange operations

* Removing the IsIndividualAddOperationCheck

Author: dipeshmsft

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Application.cs

@@ -1734,12 +1734,17 @@ internal void InvalidateResourceReferences(ResourcesChangeInfo info)
         {
             _resourcesInitialized = true;
 
-            if(!ThemeManager.IgnoreAppResourcesChange)
-            {
-                if(ThemeManager.SyncThemeModeAndResources())
-                {
-                    return;
-                }
+            // Sync needs to be performed only under the following conditions:
+            //  - the resource change event raised is due to a collection change
+            //      i.e. it is not a IsIndividualResourceAddOperation
+            //  - the event is not raised due to the change in Application.ThemeMode
+            //      i.e. SkipAppThemeModeSyncing is set to true
+            //  - if application's ThemeMode and Resources sync is enabled.
+            //      i.e. IsAppThemeModeSyncEnabled is set to true
+            if (!ThemeManager.SkipAppThemeModeSyncing 
+                    && ThemeManager.IsAppThemeModeSyncEnabled)
+            {
+                ThemeManager.SyncThemeMode();
             }
 
             // Invalidate ResourceReference properties on all the windows.

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/ThemeManager.cs

@@ -18,7 +18,7 @@ internal static void OnSystemThemeChanged()
     {
         if (IsFluentThemeEnabled)
         {
-            IgnoreAppResourcesChange = true;
+            SkipAppThemeModeSyncing = true;
 
             try
             {
@@ -51,7 +51,7 @@ internal static void OnSystemThemeChanged()
             }
             finally
             {
-                IgnoreAppResourcesChange = false;
+                SkipAppThemeModeSyncing = false;
             }
 
         }
@@ -76,7 +76,7 @@ internal static void OnSystemThemeChanged()
 
     internal static void OnApplicationThemeChanged(ThemeMode oldThemeMode, ThemeMode newThemeMode)
     {
-        IgnoreAppResourcesChange = true;
+        SkipAppThemeModeSyncing = true;
 
         try
         {
@@ -107,7 +107,7 @@ internal static void OnApplicationThemeChanged(ThemeMode oldThemeMode, ThemeMode
         }
         finally
         {
-            IgnoreAppResourcesChange = false;
+            SkipAppThemeModeSyncing = false;
         }
     }
 
@@ -125,12 +125,9 @@ internal static void OnWindowThemeChanged(Window window, ThemeMode oldThemeMode,
         ApplyFluentOnWindow(window);
     }
 
-    internal static bool SyncThemeModeAndResources()
+    internal static bool SyncThemeMode()
     {
-        if (DeferSyncingThemeModeAndResources)
-            return true;
-
-        ThemeMode themeMode = GetThemeModeFromResourceDictionary(Application.Current.Resources);
+       ThemeMode themeMode = GetThemeModeFromResourceDictionary(Application.Current.Resources);
 
         if (Application.Current.ThemeMode != themeMode)
         {
@@ -140,9 +137,11 @@ internal static bool SyncThemeModeAndResources()
         return false;
     }
 
-    internal static void SyncDeferredThemeModeAndResources()
+    internal static void SyncThemeModeAndResources()
     {
-        if (Application.Current == null)
+        // Since, this is called from window there is a possiblity that the application
+        // instance is null. Hence, we need to check for null.
+        if(Application.Current == null) 
             return;
 
         ThemeMode themeMode = Application.Current.ThemeMode;
@@ -317,7 +316,7 @@ private static void ApplyStyleOnWindow(Window window, bool useLightColors)
 
     #region Internal Properties
 
-    internal static bool DeferSyncingThemeModeAndResources { get; set; } = true;
+    internal static bool IsAppThemeModeSyncEnabled { get; set; } = false;
 
     internal static bool IsFluentThemeEnabled
     {
@@ -331,7 +330,7 @@ internal static bool IsFluentThemeEnabled
 
     internal static bool DeferredAppThemeLoading { get; set; } = false;
 
-    internal static bool IgnoreAppResourcesChange { get; set; } = false;
+    internal static bool SkipAppThemeModeSyncing { get; set; } = false;
 
     internal static double DefaultFluentThemeFontSize => 14;
 

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Window.cs

@@ -2558,10 +2558,10 @@ internal void CreateSourceWindow(bool duringShow)
 
             if (Standard.Utility.IsOSWindows10OrNewer)
             {
-                if(ThemeManager.DeferSyncingThemeModeAndResources)
+                if(!ThemeManager.IsAppThemeModeSyncEnabled)
                 {
-                    ThemeManager.DeferSyncingThemeModeAndResources = false;
-                    ThemeManager.SyncDeferredThemeModeAndResources();
+                    ThemeManager.SyncThemeModeAndResources();
+                    ThemeManager.IsAppThemeModeSyncEnabled = true;
                 }
 
                 if(ThemeManager.IsFluentThemeEnabled)