DataGridView CheckBox events

Question

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?

Answer 1

You can use the CellValidating event and the e.FormattedValue will have the changed value. If you perform some check, and dont want the value to update, set e.Cancel to true.

Here is the example from the FormattedValue page:

private void dataGridView1_CellValidating(object sender,
    DataGridViewCellValidatingEventArgs e)
{
    dataGridView1.Rows[e.RowIndex].ErrorText = "";
    int newInteger;

    // Don't try to validate the 'new row' until finished 
    // editing since there
    // is not any point in validating its initial value.
    if (dataGridView1.Rows[e.RowIndex].IsNewRow) { return; }
    if (!int.TryParse(e.FormattedValue.ToString(),
        out newInteger) || newInteger < 0)
    {
        e.Cancel = true;
        dataGridView1.Rows[e.RowIndex].ErrorText = "the value must be a non-negative integer";
    }
}

Answer 2

Ultimately, it was the CurrentCellDirtyStateChanged event that does it, but you need to do it in the right way. And the right way is MSDN's, though it doesn't make sense at first glance.

A fragment from above, and what I ultimately did is below:

    // 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;
    }
}

void dgvSysGrid_CurrentCellDirtyStateChanged(object sender, EventArgs e)
{
    if (dgvSysGrid.IsCurrentCellDirty)
    {
        dgvSysGrid.CommitEdit(DataGridViewDataErrorContexts.Commit);
    }
}

Basically, all that's happening is the CurrentCellDirtyStateChanged event triggers the CellValueChanged event, and that's it. If you just attach the CellValueChanged event, then it only triggers AFTER you have left the cell. I don't know why exactly (considering it's a checkbox, isn't it "done" immediately?), but that's what happens. And the code as above works, in that the check box changes go in RIGHT away when clicking it. So it works.