Why is my C# array of objects fully populated when some of them should be null?

Hi All

Aplogies if this is more a c# query, but I can't find any details generally so far.

I have a 2D map that represents legal positions for creatures and players in the world. The world is 3d but movement is tile based. I have a serializable class for each tile and a 1d array I treat as 2d via a GetTile() method. Some of my tiles are not accessible and so I wanted to set the array location to null, but it doesn't appear to work - when I inspect the array on load, each index contains a tile class, although where the tiles should be null they are only partially constructed?

Any help greatly apprechiated!

[Edit] Thanks for all the help so far. Here's the code with the bodies edited out

 [System.Serializable]
 public class BVMapTile
 {  // [EDIT] clearly a tile isn't empty but the contents probably don't tell you much
 }
 
 [System.Serializable]
 public class BVMap2D : MonoBehaviour
 {   // map data
     public int MaxX = 0;
     public int MaxZ = 0;
     public BVMapTile[] Tiles = null; // array is single but treated like 2D
 
     // gets a tile
     public BVMapTile GetTile(int x, int z)
     {  // return the tile specified
        return Tiles[x * MaxZ + z];
     }
     
     public void SetTile(int x, int z, BVMapTile tile)
     {  // set the tile
        Tiles[x * MaxZ + z] = tile;
     }
 }
 
 [CustomEditor(typeof(BVMap2D))]
 public class BVMap2DEditor : Editor
 {
     static bool m_render_boxes = true;
     
     void OnSceneGUI()
     {  // [EDIT] I'm drawing some handles here
     }
     
     [DrawGizmo(GizmoType.NotSelected)]
     static void RenderLevelHullGizmo(GameObject obj, GizmoType type)
     {  // if the selection is same we might care
        if(!Selection.Contains(obj)) return;
         
        // [EDIT] I'm drawing some gizmos here, I look for the component type on the GameObject and bail if its not there
     }
     
     Vector3 m_move_height = new Vector3(0, 1, 0);   // if we collide at this height we cannot pass between squares
     Vector3 m_sight_height = new Vector3(0, 1.5f, 0);  // if we collide at this height we cannot see between squares
     
     // map of calculated grounds positions
     Dictionary<BVMapTile, Vector3> m_calculated_ground_positions = new Dictionary<BVMapTile, Vector3>();
     
     public override void OnInspectorGUI()
     {  // get the map
         BVMap2D map = target as BVMap2D;
         Transform t = map.transform;
         
         // build map button
         if(GUILayout.Button("Build Map"))
         {  // warning!
            // clear map of ground positions
            m_calculated_ground_positions.Clear();
             
            // calculate the size of the map, from the handles in the scene
            Vector3 size = map.UpperBounds;
            size -= map.LowerBounds;
            int max_x = (int) ((size.x + 0.2f) / BVMap2DConstants.TileSize);
            int max_z = (int) ((size.z + 0.2f) / BVMap2DConstants.TileSize);
             
            // create a new map!
            map.Tiles = new BVMapTile[max_x * max_z];
            map.MaxX = max_x;
            map.MaxZ = max_z;
             
            // [EDIT]
            // *** The Relevant Collision Models are parsed to decide whether the tile position is accessible. ***
             
            // the final pass will decides whether the tile is closed
            for(int x=0; x<max_x; ++x)
            {  // for each z tile
               for(int z=0; z<max_z; ++z)
               {  // get  the tile we are on
                  BVMapTile tile = map.GetTile(x, z);
                  tile.DetermineClosed();
                     
                  // if the tile has an entry, set the ground position
                  tile.HaveGroundPosition = tile.HaveGroundPosition || m_calculated_ground_positions.TryGetValue(tile, out tile.GroundPosition);
                  if(!tile.HaveGroundPosition || !tile.TileOpen)
                  {  // this sets the tile in the array to null
                     map.SetTile(x,z, null);
                  }
               }
            }
         }
         
         if(GUI.changed)
             EditorUtility.SetDirty(target);
     }
 }

Apologies if the code is a bit odd looking - I have trouble pasting code into Unity Answers. Hopefully I didn't edit away too much.

Some points to note:

• I am using a public 1d array to benefit from Unity's serialisation (2d arrays don't get serialised)

• It seems I may not want to benefit from Unity's in built serialisation given answers to date...

• The tiles are serializable classes

• I'm setting the contents of the array in a custom editor which boils collision models within an array defined by two handles down to a 2D grid.

This looks like so in the editor for anyone who might be interested:

I'll respond to comments below, but it looks like the Unity default serialisation is getting in my way a little - how can I work around this?

Thanks Ian H