How to tick all checkboxes

I have a gridview control on my form.Its first column is checkboxcolumn and the other one textboxcolumn.I am populating Textbox columns with some string values coming from list

like this way

for (int i = 0; i < listeList.Count; i++)
                {
                    dataGridView1.Rows.Add();
                    dataGridView1.Rows[i].Cells[1].Value = listeList[i];
                } 

What am i trying to do is to select all the checboxes in the gridview once the user click button How can I do this

Here is what I have tried

private void btnselectAll_Click(object sender, EventArgs e)
    {


        foreach (DataGridViewRow row in dataGridView1.Rows)
        {

           // row.Cells[0].Value = "true";

            //if (row.Cells[0].Value != ull)
            //{
            //    if (Convert.ToBoolean(row.Cells[0].Value))
            //    {
            //        MessageBox.Show(row.Cells[1].Value.ToString());
            //    }
            //}

        }

    }