How to select multiple cells in gridview using shift key press

As the .net default action will also update the slectedrows of your datagridview you need to have an array to reserve the old selections:


DataGridViewRow[] old;


which will be updated at CellMouseDown (before the default .net action modify your selections):


after that, you can do your changes in RowHeaderMouseClick (as RowHeaderSelect is the default datagridview selectionmode) or use CellMouseClick for FullRowSelect and reselect those old selected rows:

private void dataGridView1_RowHeaderMouseClick(object sender, DataGridViewCellMouseEventArgs e)
{
    foreach (DataGridViewRow gr in old)
    {
        if (gr == dataGridView1.CurrentRow)
        {
            gr.Selected = false;
        }
        else
        {
            gr.Selected = true;
        }
    }
}