Default behavior of a DataGridViewComboBoxCell is that it doesn't support typing into the cell.

But you could have a request from the client who wants to have enabled typing in a Combobox cell. In order to achieve this, you need to perform two things:

- the DropDownStype property of the ComboBox editing control needs to be set to DropDown. This will enable typing in the combobox.

- ensure that the value that the user typed into the cell is added to the combo box items collection. A combo box cells value has to be in the items collection, otherwise a DataError event will be fired, so that's the reason why you need to perform this step.

You can add the value to the items collection could be done in the CellValidating event handler.

private void dataGridView1_CellValidating(object sender,
     DataGridViewCellValidatingEventArgs e)
{
    if (e.ColumnIndex == comboBoxColumn.DisplayIndex)
    {
        if (!this.comboBoxColumn.Items.Contains(e.FormattedValue))
        {
            this.comboBoxColumn.Items.Add(e.FormattedValue);
        }
    }
}
 
private void dataGridView1_EditingControlShowing(object sender,
    DataGridViewEditingControlShowingEventArgs e)
{
    if (this.dataGridView1.CurrentCellAddress.X == comboBoxColumn.DisplayIndex)
    {
        ComboBox cb = e.Control as ComboBox;
        if (cb != null)
        {
            cb.DropDownStyle = ComboBoxStyle.DropDown;
         }
    }
}