Question

How do I force only a single checkbox to be checked in a column of a Datagridview?

Answer 1

You will have to subscribe for the CellValueChanged event of the grid and depending on the check state of the current cell, loop the DataGridView and set true/false as Value for the other cells.

void grd_CellValueChanged(object sender, DataGridViewCellEventArgs e)
{
      if ((sender as DataGridView).CurrentCell is DataGridViewCheckBoxCell)
      {
           if (Convert.ToBoolean(((sender as DataGridView).CurrentCell as DataGridViewCheckBoxCell).Value))
           {
                   // Maybe have a method which does the
                    //loop and set value except for the current cell
            }
        }
}