I'm making a DataGridView with a series of Checkboxes in it with the same labels horizontally and vertically. Any labels that are the same, the checkboxes will be inactive, and I only want one of the two "checks" for each combination to be valid. The following screenshot shows what I have:

Anything that's checked on the lower half, I want UN-checked on the upper. So if [quux, spam] (or [7, 8] for zero-based co-ordinates) is checked, I want [spam, quux] ([8, 7]) un-checked. What I have so far is the following:

    dgvSysGrid.RowHeadersWidthSizeMode = DataGridViewRowHeadersWidthSizeMode.AutoSizeToAllHeaders;
    dgvSysGrid.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;
    string[] allsysNames = { "heya", "there", "lots", "of", "names", "foo", "bar", "quux", "spam", "eggs", "bacon" };

    // Add a column for each entry, and a row for each entry, and mark the "diagonals" as readonly
    for (int i = 0; i < allsysNames.Length; i++)
    {
        dgvSysGrid.Columns.Add(new DataGridViewCheckBoxColumn(false));
        dgvSysGrid.Columns[i].HeaderText = allsysNames[i];
        dgvSysGrid.Rows.Add();
        dgvSysGrid.Rows[i].HeaderCell.Value = allsysNames[i];
        // Mark all of the "diagonals" as unable to change
        DataGridViewCell curDiagonal = dgvSysGrid[i, i];
        curDiagonal.ReadOnly = true;
        curDiagonal.Style.BackColor = Color.Black;
        curDiagonal.Style.ForeColor = Color.Black;
    }

    // Hook up the event handler so that we can change the "corresponding" checkboxes as needed
    //dgvSysGrid.CurrentCellDirtyStateChanged += new EventHandler(dgvSysGrid_CurrentCellDirtyStateChanged);
    dgvSysGrid.CellValueChanged += new DataGridViewCellEventHandler(dgvSysGrid_CellValueChanged);

}

void dgvSysGrid_CellValueChanged(object sender, DataGridViewCellEventArgs e)
{
    Point cur = new Point(e.ColumnIndex, e.RowIndex);

    // Change the diagonal checkbox to the opposite state
    DataGridViewCheckBoxCell curCell = (DataGridViewCheckBoxCell)dgvSysGrid[cur.X, cur.Y];
    DataGridViewCheckBoxCell diagCell = (DataGridViewCheckBoxCell)dgvSysGrid[cur.Y, cur.X];
    if ((bool)(curCell.Value) == true)
    {
        diagCell.Value = false;
    }
    else
    {
        diagCell.Value = true;
    }
}

/// <summary>
/// Change the corresponding checkbox to the opposite state of the current one
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
void dgvSysGrid_CurrentCellDirtyStateChanged(object sender, EventArgs e)
{
    Point cur = dgvSysGrid.CurrentCellAddress;

    // Change the diagonal checkbox to the opposite state
    DataGridViewCheckBoxCell curCell = (DataGridViewCheckBoxCell)dgvSysGrid[cur.X, cur.Y];
    DataGridViewCheckBoxCell diagCell = (DataGridViewCheckBoxCell)dgvSysGrid[cur.Y, cur.X];
    if ((bool)(curCell.Value) == true)
    {
        diagCell.Value = false;
    }
    else
    {
        diagCell.Value = true;
    }
} 

The problem comes is that the cell value changed always seems to be "one behind" where you actually click if I use the CellValueChanged event, and I'm not sure how to get the current cell if I'm in the "dirty" state as curCell comes in as a null (suggesting the current cell address is wrong somehow, but I didn't try and get that value out) meaning that path isn't working at all.

Basically, how do I get the "right" address with the right boolean value so that my flipping algorithm will work?