{"category": "Unity Engine/Editor/Extensions", "keywords": "Unity, Editor, UI, Odin, Foldout, Collapse, List, Element"} Odin extension for foldout elements in list.

OdinFoldoutableListElement.cs

// Odin extension for foldout elements in list.
// Example:
//   [Serializable]
//   public class MyData1 : IFoldoutableInList
//   {
//       // members...
//   }
//   [Serializable]
//   public class MyData2 : IForceFoldoutableInList
//   {
//       // members...
//   }
//   public class Test : MonoBehaviour
//   {
//       [ElementFoldoutable]
//       public List<MyData1> dataList1 = new List<MyData1>();
//       public List<MyData2> dataList2 = new List<MyData2>();
//   }

using System;
using System.Collections;
using System.Diagnostics;
using Sirenix.OdinInspector.Editor;
using UnityEditor;
using UnityEngine;

// Put the following classes to the Runtime folder
public interface IFoldoutableInList { } // Work with ElementFoldoutableAttribute
public interface IForceFoldoutableInList : IFoldoutableInList { } // No need to use ElementFoldoutableAttribute
[Conditional("UNITY_EDITOR")]
public class ElementFoldoutableAttribute : Attribute { } // Work with IFoldoutableInList

// Put the following class to the Editor folder
public class FoldoutableListElementDrawer : OdinValueDrawer<IFoldoutableInList> // use OdinValueDrawer<object> for all types
{
    protected override void DrawPropertyLayout(GUIContent label)
    {
        if (!(Property.Parent.ValueEntry.WeakSmartValue is IList))
        {
            CallNextDrawer(label);
            return;
        }

        string propertyLabel = null;
        foreach (InspectorProperty child in Property.Children)
        {
            if (child.Info.TypeOfValue == typeof(string))
            {
                string childValue = child.ValueEntry.WeakSmartValue?.ToString();
                if (!string.IsNullOrEmpty(childValue))
                {
                    propertyLabel = childValue;
                }
                break;
            }
        }
        propertyLabel ??= $"Element {Property.Index}";

        Property.State.Expanded = EditorGUILayout.Foldout(Property.State.Expanded, propertyLabel);
        if (!Property.State.Expanded)
        {
            return;
        }

        using (new EditorGUI.IndentLevelScope())
        {
            CallNextDrawer(label);
        }
    }

    protected override bool CanDrawValueProperty(InspectorProperty property)
    {
        if (typeof(IForceFoldoutableInList).IsAssignableFrom(property.Info.TypeOfValue))
        {
            return true && base.CanDrawValueProperty(property);
        }

        foreach (Attribute attribute in property.Attributes)
        {
            if (attribute is ElementFoldoutableAttribute)
            {
                return true && base.CanDrawValueProperty(property);
            }
        }

        return false;
    }
}

There is a simpler way to achieve foldoutable list elements:

• Add Sirenix.OdinInspector.ListDrawerSettingsAttribute to the list and assign values to the ShowIndexLabel and ListElementLabelName parameters.
• Make sure there is a field or property in the type of the list element with a name matching the value assigned to the ListElementLabelName parameter (in this example, the name is "_comment").