Question

I want to only allow the user to enter 0..9, “.” and backspace in my DGV. I thought the KeyDown event might be the ticket, with something like this:

private void dataGridViewPlatypi_KeyDown(object sender, KeyEventArgs args)
{
    args.Handled = !args.KeyCode.Equals(Keys.Decimal); // etc. - add other allowed vals
    if (args.Handled)
    {
        args.SuppressKeyPress = true;
    }
}

…but that doesn’t work/has no effect.

I researched and found this: DataGridView keydown event not working in C#

…which led me to creating a custom DGV class with this:

protected override bool ProcessCmdKey(ref System.Windows.Forms.Message msg, System.Windows.Forms.Keys keyData)
{
    if ((!keyData.Equals(Keys.Decimal)) &&
        (!keyData.Equals(Keys.???))) // etc.
    {
        //suppress the key somehow
    }
    return base.ProcessCmdKey(msg, keyData); // <-- should this be in an "else" block?
}

…but as you can tell from the “???” and the “somehow” comment, I don’t know how to test for the other keys I want to allow (0..9 and backspace)

UPDATE

With able assistance from two respondents, it’s now working just great:

I started off with Hans Passant’s code here to create a custom DGV-derived control to solve the moveable final row problem:

removing the empty gray space in datagrid in c#

…and then added code based on LarsTech’s to filter out unwanted entries in the DGV.

To be precise, this is the exact logic I used to override ProcessCmdKey():

protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
    if (char.IsNumber(Convert.ToChar(keyData)) || 
        char.IsControl(Convert.ToChar(keyData)) || 
        (keyData >= Keys.NumPad0 && keyData <= Keys.NumPad9) ||
        (keyData == Keys.Space) ||
        (keyData == Keys.Back) ||
        (keyData == Keys.Decimal))
    {
        return false;
    }
    return true;
}

Answer 1

Handling the keys of a text input control is almost never 100%. You might want to investigate using a MaskedTextBox control in the DataGridView in this Code Project.

For the override, this code will get you close:

protected override bool ProcessCmdKey(ref Message msg, Keys keyData) {
  if (
    (keyData >= Keys.D0 && keyData <= Keys.D9) ||
    (keyData >= Keys.NumPad0 && keyData <= Keys.NumPad9) ||
    (keyData == Keys.Decimal | keyData == Keys.OemPeriod) ||
    (keyData == Keys.Back | keyData == Keys.Delete) ||
    (keyData == Keys.Left | keyData == Keys.Up | keyData == Keys.Right | keyData == Keys.Down) ||
    (keyData == Keys.Tab | keyData == Keys.Home | keyData == Keys.End | keyData == Keys.Enter)
    ) {
    return false;
  }

  return true;
}