Major refactor.

Core now formed and contains all useful utility to create custom ui with restrictions.
Many methods was extracted from different classes and moved to core.

Undo is now supported(because unity's undo bug seems to be fixed).

Example now moved into same level separate folder.

Assets/Textus/SerializeReferenceUI/Core/ManagedReferenceUtility.cs

@@ -0,0 +1,95 @@
+#if UNITY_EDITOR
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using UnityEditor;
+using UnityEngine;
+using Object = UnityEngine.Object;
+
+public static class ManagedReferenceUtility
+{
+    /// Creates instance of passed type and assigns it to managed reference
+    public static object AssignNewInstanceOfTypeToManagedReference(this SerializedProperty serializedProperty, Type type)
+    {
+        var instance = Activator.CreateInstance(type);
+        
+        serializedProperty.serializedObject.Update(); 
+        serializedProperty.managedReferenceValue = instance;
+        serializedProperty.serializedObject.ApplyModifiedProperties(); 
+        
+        return instance;
+    }
+
+    /// Sets managed reference to null
+    public static void SetManagedReferenceToNull(this SerializedProperty serializedProperty)
+    {
+        serializedProperty.serializedObject.Update();
+        serializedProperty.managedReferenceValue = null;
+        serializedProperty.serializedObject.ApplyModifiedProperties(); 
+    }
+
+    /// Collects appropriate types based on managed reference field type and filters. Filters all derive
+    public static IEnumerable<Type> GetAppropriateTypesForAssigningToManagedReference(this SerializedProperty property, List<Func<Type, bool>> filters = null)
+    {
+        var fieldType = property.GetManagedReferenceFieldType();
+        return GetAppropriateTypesForAssigningToManagedReference(fieldType, filters);
+    }
+
+    /// Filters derived types of field typ parameter and finds ones whose are compatible with managed reference and filters.
+    public static IEnumerable<Type> GetAppropriateTypesForAssigningToManagedReference(Type fieldType, List<Func<Type, bool>> filters = null)
+    {
+        var appropriateTypes = new List<Type>();
+
+        // Get and filter all appropriate types
+        var derivedTypes = TypeCache.GetTypesDerivedFrom(fieldType);
+        foreach (var type in derivedTypes)
+        {
+            // Skips unity engine Objects (because they are not serialized by SerializeReference)
+            if (type.IsSubclassOf(typeof(Object)))
+                continue;
+            // Skip abstract classes because they should not be instantiated
+            if (type.IsAbstract)
+                continue;
+            // Filter types by provided filters if there is ones
+            if (filters != null && filters.All(f => f == null || f.Invoke(type)) == false) 
+                continue;
+
+            appropriateTypes.Add(type);
+        }
+
+        return appropriateTypes;
+    }
+    
+    /// Gets real type of managed reference
+    public static Type GetManagedReferenceFieldType(this SerializedProperty property)
+    {
+        var realPropertyType = GetRealTypeFromTypename(property.managedReferenceFieldTypename);
+        if (realPropertyType != null) 
+            return realPropertyType;
+        
+        Debug.LogError($"Can not get field type of managed reference : {property.managedReferenceFieldTypename}");
+        return null;
+    }
+    
+    /// Gets real type of managed reference's field typeName
+    public static Type GetRealTypeFromTypename(string stringType)
+    {
+        var names = GetSplitNamesFromTypename(stringType);
+        var realType = Type.GetType($"{names.ClassName}, {names.AssemblyName}");
+        return realType;
+    }
+    
+    /// Get assembly and class names from typeName
+    public static (string AssemblyName, string ClassName) GetSplitNamesFromTypename(string typename)
+    {
+        if (string.IsNullOrEmpty(typename))  
+            return ("","");
+        
+        var typeSplitString = typename.Split(char.Parse(" "));
+        var typeClassName = typeSplitString[1];
+        var typeAssemblyName = typeSplitString[0];
+        return (typeAssemblyName,  typeClassName); 
+    }
+}
+#endif

Assets/Textus/SerializeReferenceUI/Core/SerializeReferenceGenericSelectionMenu.cs

@@ -9,7 +9,7 @@ using UnityEngine;
 public static class SerializeReferenceGenericSelectionMenu
 {
     /// Purpose.
-    /// This is generic selection menu.
+    /// This is generic selection menu.   
     /// Filtering. 
     /// You can add substring filter here to filter by search string.
     /// As well ass type or interface restrictions.
@@ -22,72 +22,39 @@ public static class SerializeReferenceGenericSelectionMenu
         context.ShowAsContext();
     }  
     
-    
     private static void FillContextMenu(IEnumerable<Func<Type, bool>> enumerableFilters, GenericMenu contextMenu, SerializedProperty property)
     {
         var filters = enumerableFilters.ToList();// Prevents possible multiple enumerations
         
         // Adds "Make Null" menu command
-        contextMenu.AddItem(new GUIContent("Null"), false, () => MakeSerializedPropertyNull(property));
-        
-        // Find real type of managed reference
-        var realPropertyType = SerializeReferenceTypeNameUtility.GetRealTypeFromTypename(property.managedReferenceFieldTypename);
-        if (realPropertyType == null)
-        { 
-            Debug.LogError("Can not get type from");
-            return;
-        }
+        contextMenu.AddItem(new GUIContent("Null"), false, property.SetManagedReferenceToNull);
          
-        // Get and filter all appropriate types
-        var types = TypeCache.GetTypesDerivedFrom(realPropertyType);
-        foreach (var type in types)
-        { 
-            // Skips unity engine Objects (because they are not serialized by SerializeReference)
-            if(type.IsSubclassOf(typeof(UnityEngine.Object)))
-                continue;
-            // Skip abstract classes because they should not be instantiated
-            if(type.IsAbstract)    
-                continue;
-            // Filter types by provided filters if there is ones
-            if (FilterTypeByFilters(filters, type) == false) 
-                continue; 
-                
-            AddItemToContextMenu(type, contextMenu, property); 
-        } 
-    } 
-
-    private static void MakeSerializedPropertyNull(SerializedProperty serializedProperty)
-    {
-        serializedProperty.serializedObject.Update();
-        serializedProperty.managedReferenceValue = null;
-        serializedProperty.serializedObject.ApplyModifiedPropertiesWithoutUndo(); // undo is bugged for now
+        // Collects appropriate types
+        var appropriateTypes = property.GetAppropriateTypesForAssigningToManagedReference(filters);
+        
+        // Adds appropriate types to menu
+        foreach (var appropriateType in appropriateTypes)
+            AddItemToContextMenu(appropriateType, contextMenu, property); 
     }
     
     private static void AddItemToContextMenu(Type type, GenericMenu genericMenuContext, SerializedProperty property)
     {
         var assemblyName =  type.Assembly.ToString().Split('(', ',')[0];
         var entryName = type + "  ( " + assemblyName + " )";
-        genericMenuContext.AddItem(new GUIContent(entryName), false, AssignNewInstanceOfType, new AssignInstanceGenericMenuParameter(type, property));
+        genericMenuContext.AddItem(new GUIContent(entryName), false, AssignNewInstanceCommand, new GenericMenuParameterForAssignInstanceCommand(type, property));
     }
     
-    private static void AssignNewInstanceOfType(object objectGenericMenuParameter )
+    private static void AssignNewInstanceCommand(object objectGenericMenuParameter )
     {
-        var parameter = (AssignInstanceGenericMenuParameter) objectGenericMenuParameter;
+        var parameter = (GenericMenuParameterForAssignInstanceCommand) objectGenericMenuParameter;
         var type = parameter.Type;
         var property = parameter.Property;
-        var instance = Activator.CreateInstance(type); 
-        property.serializedObject.Update();
-        property.managedReferenceValue = instance;
-        property.serializedObject.ApplyModifiedPropertiesWithoutUndo(); // undo is bugged for now
-    }   
-    
-    private static  bool FilterTypeByFilters (IEnumerable<Func<Type,bool>> filters, Type type) =>
-        filters.All(f => f == null || f.Invoke(type));
+        property.AssignNewInstanceOfTypeToManagedReference(type);
+    }
 
-    
-    private readonly struct AssignInstanceGenericMenuParameter
+    private readonly struct GenericMenuParameterForAssignInstanceCommand
     {
-        public AssignInstanceGenericMenuParameter(Type type, SerializedProperty property)
+        public GenericMenuParameterForAssignInstanceCommand(Type type, SerializedProperty property)
         {
             Type = type;
             Property = property;

Assets/Textus/SerializeReferenceUI/Core/SerializeReferenceTypeNameUtility.cs

@@ -1,24 +0,0 @@
-using System;
-
-/// This utility exists, because serialize reference managed reference typename returns combined string
-/// and not data class that contains separate strings for assembly name and for class name (and possibly namespace name)
-public static class SerializeReferenceTypeNameUtility
-{
-    public static Type GetRealTypeFromTypename(string stringType)
-    {
-        var names = GetSplitNamesFromTypename(stringType);
-        var realType = Type.GetType($"{names.ClassName}, {names.AssemblyName}");
-        return realType;
-    }
-    
-    public static (string AssemblyName, string ClassName) GetSplitNamesFromTypename(string typename)
-    {
-        if (string.IsNullOrEmpty(typename))
-            return ("","");
-        
-        var typeSplitString = typename.Split(char.Parse(" "));
-        var typeClassName = typeSplitString[1];
-        var typeAssemblyName = typeSplitString[0];
-        return (typeAssemblyName,  typeClassName);
-    }  
-}

Assets/Textus/SerializeReferenceUI/Core/SerializeReferenceTypeRestrictionFilters.cs

@@ -1,4 +1,4 @@
-using System;
+    using System;
 using System.Linq;
 
 public static class SerializeReferenceTypeRestrictionFilters

Assets/Textus/SerializeReferenceUI/DefaultAttributes/SerializeReferenceButtonAttribute/SerializeReferenceButtonAttributeDrawer.cs

@@ -20,7 +20,7 @@ public class SerializeReferenceButtonAttributeDrawer : PropertyDrawer
         var labelPosition = new Rect(position.x, position.y, position.width, EditorGUIUtility.singleLineHeight);
         EditorGUI.LabelField(labelPosition, label);    
          
-        var typeRestrictions = SerializedReferenceUIBuiltInTypeRestrictions.GetAllBuiltInTypeRestrictions(fieldInfo);
+        var typeRestrictions = SerializedReferenceUIDefaultTypeRestrictions.GetAllBuiltInTypeRestrictions(fieldInfo);
         property.DrawSelectionButtonForManagedReference(position, typeRestrictions);
         
         EditorGUI.PropertyField(position, property, GUIContent.none, true);

Assets/Textus/SerializeReferenceUI/DefaultAttributes/SerializeReferenceMenuAttribute/SerializeReferenceMenuAttributeDrawer.cs

@@ -15,7 +15,7 @@ public class SerializeReferenceMenuAttributeDrawer : PropertyDrawer
     {
         EditorGUI.BeginProperty(position, label, property);
         
-        var typeRestrictions = SerializedReferenceUIBuiltInTypeRestrictions.GetAllBuiltInTypeRestrictions(fieldInfo);
+        var typeRestrictions = SerializedReferenceUIDefaultTypeRestrictions.GetAllBuiltInTypeRestrictions(fieldInfo);
         property.ShowContextMenuForManagedReferenceOnMouseMiddleButton(position, typeRestrictions);
         
         EditorGUI.PropertyField(position, property, true);

Assets/Textus/SerializeReferenceUI/DefaultAttributes/SerializeReferenceUIRestrictionExcludeTypes.meta

@@ -0,0 +1,8 @@
+fileFormatVersion: 2
+guid: 3fbe55d72b5fd59459fdb52e0f301ea1
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Textus/SerializeReferenceUI/DefaultAttributes/SerializeReferenceUIRestrictionIncludeTypes.meta

@@ -0,0 +1,8 @@
+fileFormatVersion: 2
+guid: c0c77910f7962a14cb85132596cb8d24
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Textus/SerializeReferenceUI/DefaultAttributes/SerializedReferenceUIDefaultTypeRestrictions.cs

@@ -2,7 +2,7 @@
 using System.Collections.Generic;
 using System.Reflection;
 
-public static class SerializedReferenceUIBuiltInTypeRestrictions
+public static class SerializedReferenceUIDefaultTypeRestrictions
 {
     public static IEnumerable<Func<Type, bool>> GetAllBuiltInTypeRestrictions(FieldInfo fieldInfo)
     {

Assets/Textus/SerializeReferenceUI/DefaultUI/SerializeReferenceInspectorButton.cs

@@ -31,7 +31,7 @@ public static class SerializeReferenceInspectorButton
         GUI.backgroundColor = backgroundColor; 
          
         
-        var names = SerializeReferenceTypeNameUtility.GetSplitNamesFromTypename(property.managedReferenceFullTypename);
+        var names = ManagedReferenceUtility.GetSplitNamesFromTypename(property.managedReferenceFullTypename);
         var className = string.IsNullOrEmpty(names.ClassName) ? "Null (Assign)" : names.ClassName;
         var assemblyName = names.AssemblyName;
         if (GUI.Button(buttonPosition, new GUIContent(className, className + "  ( "+ assemblyName +" )" )))

Assets/Textus/SerializeReferenceUIExample/ExampleOfUsageFromDifferentAssembly/TestingAnimalWorldExample/Scenes/SerializeRefereneceUIExampleScene.unity

@@ -171,19 +171,17 @@ MonoBehaviour:
   references:
     version: 1
     00000000:
-      type: {class: GreenApe, ns: , asm: SerializedReferenceExample}
+      type: {class: GoldenApe, ns: , asm: SerializedReferenceExample}
       data:
-        age: 0
-        food: {fileID: 0}
-        numberOfBones: 0
-        Tag: 
+        age: 1231
+        food: {fileID: 1131539293}
+        numberOfBones: 33
+        Tag: dd
     00000001:
-      type: {class: RedCat, ns: , asm: SerializedReferenceExample}
+      type: {class: AnimalChild, ns: , asm: AmimalWorld}
       data:
-        age: 0
+        age: 3213
         food: {fileID: 0}
-        numberOfBones: 0
-        Tag: 
     00000002:
       type: {class: , ns: , asm: }
     00000003: