Custom PropertyDrawer fails because my ScriptableObject property is not initialized in time

Hi! I try to made a custom property drawer to have a 2D grid in the inspector (I need a 3D grid actually, like a voxel buffer).

I have 3 ScriptableObjects :

• Level,

• TileGrid,

• Tile,

Each level has a reference to a tilegrid. I want the grid displaying in the inspector on level '.asset' file selection, so I made a custom PropertyDrawer related to TileGrid class.

My issue is that, when my OnGUI method is executed, an error raises when the program trying to access to a serialized property of tilegrid instance: the error say that there is no tilegrid instance. In my opinion, this is because my level instance has no correct default tilegrid value (null).

I noticed that, when I select a '.asset' level file in Unity Editor, the OnGUI function is executed before the OnEnable method of TileGrid (this is where I initialize the default tilegrid value and I don't see how to do it differently). Is someone has a solution about this?

EDIT: Confusion of mine, OnEnable is called only on object load. So how to define default ScriptableObject properties values inside an other ScriptableObject ? Is it even possible ?

Tile :

  [System.Serializable]
 [CreateAssetMenu (menuName ="Gamedata/Tile")]
 public class Tile : ScriptableObject 
 {
     public string meshFile;
     public string textureFile;
 }

TileGrid :

  [System.Serializable]
     public class TileGrid : ScriptableObject
     {
     public int dimX = 4;
     public int dimY = 4;
     private int dimZ = 1;
 
     public Tile[,,] tiles;
 
     void OnEnable()
     {
         if(tiles == null)
         {
             tiles= new Tile[dimX, dimY, dimZ];
             for(int z =0; z<dimZ; z++) {
                 for(int y = 0; y<dimY; y++) {
                     for(int x = 0; x<dimX; x++) {
                         tiles[x, y, z] = ScriptableObject.CreateInstance<Tile>();
                     }
                 }
             }
         }
     }
 }

Level:

  [CreateAssetMenu(menuName = "Gamedata/Level")]
     public class Level : ScriptableObject {
     
         public TileGrid grid;
 
 void OnEnable()
 {
         if (grid == null)
             grid = ScriptableObject.CreateInstance<TileGrid>();
 }

Custom PropertyDrawer:

 [CustomPropertyDrawer(typeof(TileGrid))]
 public class TileGridProperty : PropertyDrawer
 {
     public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
     {
         EditorGUI.PrefixLabel(position, label);
 
         int dimX = property.FindPropertyRelative("dimX").intValue; // ERROR occurs
         int dimY = property.FindPropertyRelative("dimY").intValue;
         int dimZ = property.FindPropertyRelative("dimZ").intValue;
 
         position.y += 18f;
         position.width /= dimX;
         position.height /= dimY;
 
         SerializedProperty tileGrid = property.FindPropertyRelative("tileGrid");
         for(int z=0; z < dimZ; z++) {
             SerializedProperty arrayZ = tileGrid.GetArrayElementAtIndex(z);
             for(int y=0; y < dimY; y++)  {
                 SerializedProperty arrayY = arrayZ.GetArrayElementAtIndex(y);
                 for(int x=0; x < dimX; x++) {
                     SerializedProperty arrayX = arrayY.GetArrayElementAtIndex(x);
 
                     SerializedProperty tile = arrayX.GetArrayElementAtIndex(0);
                     EditorGUI.PropertyField(position, tile, GUIContent.none);
                 }
             }
         }
     }
 
     public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
     {
         return 18f;
     }
 }