Question

I have an array of classes (Voxel) in a class. I use the following methods to add to and remove from the array. A memento pattern is used to store the action for each method so it can be undone/redone at any point.

    public void AddVoxel(int x, int y, int z)
    {
        int index = z * width * height + y * width + x;

        frames[currentFrame].Voxels[index] = new Voxel();

        // Undo/Redo history
        undoRedoHistories[currentFrame].Do(new AddMemento(index));
    }

    public void RemoveVoxel(int x, int y, int z)
    {
        int index = z * width * height + y * width + x;

        // Undo/Redo history
        undoRedoHistories[currentFrame].Do(new RemoveMemento(index, frames[currentFrame].Voxels[index]));

        frames[currentFrame].Voxels[index] = null;      // Does not update 'voxelSelected' reference
    }

In a separate class I wish to have a reference to a particular voxel in the array of voxels held by the above class.

private Voxel voxelSelected = null;

As a reference type I would like this value to automatically know when the part of the array it “points” to holds a voxel or is null. This is important when using an undo command because a voxel can be removed from the array and become null, or vice versa.

To get a voxel from the array I use the following method.

public Voxel GetVoxel(int x, int y, int z)
{
    return frames[currentFrame].Voxels[z * width * height + y * width + x];
}

I then set the reference to the voxel as follows.

public void SetVoxelSelected(ref Voxel voxel)
{
    voxelSelected = voxel;
}

    voxelMeshEditor.AddVoxel(0, 0, 0);

    var voxel = voxelMeshEditor.GetVoxel(0, 0, 0);  // Copies rather than references?

    SetVoxelSelected(ref voxel);

    Console.WriteLine(voxelSelected == null); // False

    voxelMeshEditor.RemoveVoxel(0, 0, 0);

    Console.WriteLine(voxelSelected == null); // False (Incorrect intended behaviour)

How can I correctly reference a voxel in the array so the voxelSelected value automatically updates when the array updates.

Answer 1

How can I correctly reference a voxel in the array so the voxelSelected value automatically updates when the array updates.

Don’t store a Voxel, but store the coordinates you need to get the voxel.

Instead of

Voxel voxelSelected;
public void SetVoxelSelected(ref Voxel voxel) { voxelSelected = voxel; }

have

int selectedX, selectedY, selectedZ
public void SetVoxelSelected (int x, int y, int z) { selectedX = x; ... }
public Voxel GetVoxelSelected() { return voxelMeshEditor.GetVoxel(x, y, z) }

giving

SetVoxelSelected(0, 0, 0);                     //Set selected
Console.WriteLine(GetVoxelSelected() == null); // False, CORRECT !
voxelMeshEditor.RemoveVoxel(0, 0, 0);          //REMOVE
Console.WriteLine(GetVoxelSelected() == null); // True