Unity3D editor: Rendering nested elements in sidebar

Question

In Unity, one of my MonoBehaviours has a field pointing to another object (a ScriptableObject). If I double-click that field, I can see the fields of that object. How do I render those fields into the top-level MonoBehaviour's property drawer?

In picture form

What I have

(double-click the element)

What I want

I have my own [CustomEditor] component, but I can't quite get it to work right; stuff like this:

SerializedProperty activityStack = serializedObject.FindProperty("activityStack");
EditorGUILayout.PropertyField(activityStack.GetArrayElementAtIndex(0));

just renders the "Element 0 (Idle Activity)" bit and not the actual contents of the reference.

Answer 1

Because the default PropertyField for a ScriptableObject is just the one you get: A UnityEngine.Object reference field like for GameObject and Components and other assets ;)

---

Of course you can implement what you want to achieve but that's a bit more complex and not really good for maintenance and I would not recommend it.

---

I don't know your ScriptableObject so here an example

public class ExampleSO : ScriptableObject
{
    public int SomeInt;
    [SerializeField] private string _someString;
}

and your MonoBehaviour e.g.

public class Example : MonoBehaviour
{
    public List<ExampleSO> _SOList;
}

Then the editor could look like e.g.

using UnityEditor;
using UnityEngine;

// This is the namespace for the ReorderableList
using UnityEditorInternal;

[CustomEditor(typeof(Example))]
public class ExampleEditor : Editor
{
    SerializedProperty _SOList;

    Example _example;
    MonoScript _script;

    ReorderableList _list;

    private void OnEnable()
    {
        // Link up the serializedProperty
        _SOList = serializedObject.FindProperty("_SOList");

        // get the casted target instance (only needed for drawing the script field)
        _example = (Example) target;

        // get the according script instance (only needed for drawing the script field)
        _script = MonoScript.FromMonoBehaviour(_example);

        // Set up the ReorderableList
        _list = new ReorderableList(serializedObject, _SOList, true, true, true, true)
        {
            // What shall be displayed as header for the list?
            drawHeaderCallback = (Rect rect) => EditorGUI.LabelField(rect, _SOList.displayName),

            // How is each element displayed?
            drawElementCallback = (Rect rect, int index, bool isActive, bool isFocused) =>
            {
                // Get the element in the list (SerializedProperty)
                var element = _SOList.GetArrayElementAtIndex(index);

                // and draw the default object reference field
                EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width, EditorGUIUtility.singleLineHeight), element, new GUIContent("Reference"));

                // Check if an asset is referenced - if not we are done here
                if (!element.objectReferenceValue) return;

                // Otherwise get the SerializedObject for this asset
                var elementSerializedObject = new SerializedObject(element.objectReferenceValue);

                // and all the properties (SerializedProperty) of it you want to display
                var someInt = elementSerializedObject.FindProperty("SomeInt");
                var someString = elementSerializedObject.FindProperty("_someString");

                // Similar to the OnInspectorGUI first load the current values into this serializedobject
                elementSerializedObject.Update();
                {
                    // Adding some indentation just to show that the following fields are actually belonging to the referenced asset
                    EditorGUI.indentLevel++;
                    {
                        rect = EditorGUI.IndentedRect(rect);

                        // shift down the rect by one line
                        rect.y += EditorGUIUtility.singleLineHeight;

                        // Draw the field for the Int 
                        EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width, EditorGUIUtility.singleLineHeight), someInt);

                        // Shift down the rect another line
                        rect.y += EditorGUIUtility.singleLineHeight;
  
                        // Draw the string field
                        EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width, EditorGUIUtility.singleLineHeight), someString);
                    }
                    EditorGUI.indentLevel--;
                }
                // Write back the changed values and trigger the checks for logging dirty states and Undo/Redo
                elementSerializedObject.ApplyModifiedProperties();
            },

            // How much vertical space should be reserved for each element?
            elementHeightCallback = (int index) =>
            {
                // Get the elements serialized property
                var element = _SOList.GetArrayElementAtIndex(index);

                // by default we have only the asset reference -> single line
                var lines = 1;

                // if the asset is referenced adds space for the additional fields
                if (element.objectReferenceValue) lines += 2; // or how many lines you'll need

                return lines * EditorGUIUtility.singleLineHeight;
            }
        };
    }

    public override void OnInspectorGUI()
    {
        // draw th script field
        DrawScriptField();

        // Load the current values into the serializedObject
        serializedObject.Update();
        {
            // let the ReorderableList do its magic
            _list.DoLayoutList();
        }
        // Write back the changed values into the actual instance
        serializedObject.ApplyModifiedProperties();
    }

    // Just draws the usual script field at the top of the Inspector
    private void DrawScriptField()
    {
        EditorGUI.BeginDisabledGroup(true);
        {
            EditorGUILayout.ObjectField("Script", _script, typeof(Example), false);
        }
        EditorGUI.EndDisabledGroup();

        EditorGUILayout.Space();
    }
}

Which results in the following Inspector. As you can see I opened the Isnpectors of the MonoBehaviour and two instances of the ExampleSO to show how the values are taken over to the actual instances