Auto populate default values for unity-serialized fields

Author: vanifatovvlad

Editor/TriPropertyDefinition.cs

@@ -18,6 +18,7 @@ public class TriPropertyDefinition
         private readonly List<string> _extensionErrors = new List<string>();
         private readonly MemberInfo _memberInfo;
         private readonly List<Attribute> _attributes;
+        private readonly bool _isNonPolymorphicSerializedByUnity;
 
         private TriPropertyDefinition _arrayElementDefinitionBackingField;
 
@@ -73,6 +74,10 @@ internal TriPropertyDefinition(
             _valueGetter = valueGetter;
             _valueSetter = valueSetter;
 
+            _isNonPolymorphicSerializedByUnity = memberInfo is FieldInfo fi &&
+                                                 TriUnitySerializationUtilities.IsSerializableByUnity(fi) &&
+                                                 fi.GetCustomAttribute<SerializeReference>() == null;
+
             Order = order;
             IsReadOnly = _valueSetter == null || Attributes.TryGet(out ReadOnlyAttribute _);
 
@@ -143,7 +148,19 @@ public bool TryGetMemberInfo(out MemberInfo memberInfo)
 
         public object GetValue(TriProperty property, int targetIndex)
         {
-            return _valueGetter(property, targetIndex);
+            var value = _valueGetter(property, targetIndex);
+
+            if (value == null && _isNonPolymorphicSerializedByUnity)
+            {
+                value = TriUnitySerializationUtilities.PopulateUnityDefaultValueForType(FieldType);
+
+                if (value != null)
+                {
+                    _valueSetter?.Invoke(property, targetIndex, value);
+                }
+            }
+
+            return value;
         }
 
         public bool SetValue(TriProperty property, object value, int targetIndex, out object parentValue)

Editor/Utilities/TriUnitySerializationUtilities.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Reflection;
 using UnityEngine;
@@ -23,13 +24,13 @@ public static bool IsSerializableByUnity(FieldInfo fieldInfo)
 
             if (fieldInfo.IsPublic || fieldInfo.GetCustomAttribute<SerializeField>() != null)
             {
-                return IsTypeSerializable(fieldInfo.FieldType, allowCollections: true);
+                return IsTypeSerializable(fieldInfo.FieldType);
             }
 
             return false;
         }
 
-        private static bool IsTypeSerializable(Type type, bool allowCollections)
+        public static bool IsTypeSerializable(Type type, bool allowCollections = true)
         {
             if (type == typeof(object))
             {
@@ -97,6 +98,11 @@ private static bool IsTypeSerializable(Type type, bool allowCollections)
                 }
             }
 
+            if (typeof(IEnumerable).IsAssignableFrom(type))
+            {
+                return false;
+            }
+
             if (type.GetCustomAttribute<SerializableAttribute>() != null)
             {
                 return true;
@@ -106,5 +112,41 @@ private static bool IsTypeSerializable(Type type, bool allowCollections)
 
             return false;
         }
+
+        internal static object PopulateUnityDefaultValueForType(Type type)
+        {
+            if (type == typeof(string))
+            {
+                return string.Empty;
+            }
+
+            if (typeof(Object).IsAssignableFrom(type))
+            {
+                return null;
+            }
+
+            if (type.IsEnum)
+            {
+                var values = Enum.GetValues(type);
+                return values.Length > 0 ? values.GetValue(0) : Enum.ToObject(type, 0);
+            }
+
+            if (type.IsValueType)
+            {
+                return Activator.CreateInstance(type);
+            }
+
+            if (type.IsArray && type.GetElementType() is var elementType && elementType != null)
+            {
+                return Array.CreateInstance(elementType, 0);
+            }
+
+            if (type.GetConstructor(Type.EmptyTypes) != null)
+            {
+                return Activator.CreateInstance(type);
+            }
+
+            return null;
+        }
     }
 }