Fix applying new array Size when SerializedProperty was dirty

Author: arimger

Assets/Editor Toolbox/Editor/Internal/ReorderableListBase.cs

@@ -260,6 +260,25 @@ private void DoDraggingAndSelection()
             }
         }
 
+        protected bool TryGetNewValueOverride(SerializedProperty property, int index, out object newValue)
+        {
+            if (overrideNewElementCallback != null)
+            {
+                newValue = overrideNewElementCallback(index);
+                return true;
+            }
+
+            if (property.propertyType == SerializedPropertyType.ManagedReference || 
+                property.propertyType == SerializedPropertyType.Generic)
+            {
+                newValue = null;
+                return true;
+            }
+
+            newValue = default;
+            return false;
+        }
+
         protected abstract void DoListMiddle();
 
         protected abstract void DoListMiddle(Rect middleRect);
@@ -457,27 +476,24 @@ public void CutKeyboardFocus()
 
         public void AppendElement()
         {
-            var newSize = Size.intValue + 1;
-            Size.intValue = newSize;
+            var newSize = List.arraySize + 1;
+            List.arraySize = newSize;
             Index = newSize - 1;
 
             List.serializedObject.ApplyModifiedProperties();
             var property = List.GetArrayElementAtIndex(Index);
-            var fieldInfo = property.GetFieldInfo();
-            if (fieldInfo == null)
+            if (!TryGetNewValueOverride(property, Index, out var newValue))
             {
                 return;
             }
 
-            if (overrideNewElementCallback != null)
-            {
-                var newValue = overrideNewElementCallback(Index);
-                property.SetProperValue(fieldInfo, newValue, false);
-            }
-            else
+            var fieldInfo = property.GetFieldInfo();
+            if (fieldInfo == null)
             {
-                property.SetProperValue(fieldInfo, null, false);
+                return;
             }
+
+            property.SetProperValue(fieldInfo, newValue, false);
         }
 
         public void RemoveElement()
@@ -660,7 +676,7 @@ public virtual void DrawStandardHeader(Rect rect)
                 sizeValue = Mathf.Max(EditorGUI.DelayedIntField(rect, sizeValue, Style.sizePropertyStyle), 0);
                 if (EditorGUI.EndChangeCheck())
                 {
-                    property.intValue = sizeValue;
+                    List.arraySize = sizeValue;
                 }
 
                 EditorGUI.EndProperty();