Fix serialization of ControlReference when used in prefabs

#3262

Source/Engine/Serialization/JsonConverters.cs

@@ -492,6 +492,16 @@ namespace FlaxEngine.Json
             writer.WriteValue(JsonSerializer.GetStringID(&id));
         }
 
+        /// <inheritdoc />
+        public override void WriteJsonDiff(JsonWriter writer, object value, object other, Newtonsoft.Json.JsonSerializer serializer)
+        {
+            if (value is IControlReference valueRef &&
+                other is IControlReference otherRef &&
+                JsonSerializer.SceneObjectEquals(valueRef.UIControl, otherRef.UIControl))
+                return;
+            base.WriteJsonDiff(writer, value, other, serializer);
+        }
+
         /// <inheritdoc />
         public override object ReadJson(JsonReader reader, Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)
         {
@@ -499,7 +509,7 @@ namespace FlaxEngine.Json
             if (reader.TokenType == JsonToken.String && result is IControlReference controlReference)
             {
                 JsonSerializer.ParseID((string)reader.Value, out var id);
-                controlReference.UIControl = Object.Find<UIControl>(ref id);
+                controlReference.Load(Object.Find<UIControl>(ref id));
             }
             return result;
         }

Source/Engine/Serialization/JsonSerializer.cs

@@ -228,6 +228,23 @@ namespace FlaxEngine.Json
             CacheManagedOnly.Dispose();
         }
 
+        /// <summary>
+        /// The default implementation of the values comparision function used by the serialization system.
+        /// </summary>
+        /// <param name="objA">The object a.</param>
+        /// <param name="objB">The object b.</param>
+        /// <returns>True if both objects are equal, otherwise false.</returns>
+        public static bool SceneObjectEquals(SceneObject objA, SceneObject objB)
+        {
+            if (objA == objB)
+                return true;
+            if (objA == null || objB == null)
+                return false;
+            if (objA.HasPrefabLink && objB.HasPrefabLink)
+                return objA.PrefabObjectID == objB.PrefabObjectID;
+            return false;
+        }
+
         /// <summary>
         /// The default implementation of the values comparision function used by the serialization system.
         /// </summary>