Improve the performance of merged ResourceDictionaries

src/Shared/HandyControl_Shared/Themes/SharedResourceDictionary.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Collections.Generic;
+using System.Windows;
+using HandyControl.Tools;
+
+namespace HandyControl.Themes
+{
+    public class SharedResourceDictionary : ResourceDictionary
+    {
+        public static Dictionary<Uri, ResourceDictionary> SharedDictionaries = new Dictionary<Uri, ResourceDictionary>();
+
+        private Uri _sourceUri;
+
+        public new Uri Source
+        {
+            get => DesignerHelper.IsInDesignMode ? base.Source : _sourceUri;
+            set
+            {
+                if (value == null) return;
+                if (DesignerHelper.IsInDesignMode)
+                {
+                    base.Source = value;
+                    return;
+                }
+                _sourceUri = value;
+
+                if (!SharedDictionaries.ContainsKey(value))
+                {
+                    base.Source = value;
+                    SharedDictionaries.Add(value, this);
+                }
+                else
+                {
+                    MergedDictionaries.Add(SharedDictionaries[value]);
+                }
+            }
+        }
+    }
+}