changing the current cell selection of datagridview to row select

i have a windows form in which we have a datagridview. the property of that is cell select. and i have a contextmenustrip in which there is a menu named select all when select all is clicked it should change the property of datagridview **of the selected cell** to the full row select and the selection should be on the same row which i have clicked. the problem is when i click on a cell the default property is cell select and when i click on select all of the context menustrip the selected cell is not selected and i have to reselect that row i want that when the form opens and when i click on particular cell and when i click on select all of the contextmenustrip is clicked then the same row should be selected on which i have clicked the cell previously
this is my code

private void selectAllToolStripMenuItem_Click(object sender, EventArgs e)
   {

       dataGridView1.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
   }

Tags: C#