Check All Checkbox items on DataGridView

DataGridViewCheckBoxCell chk = (DataGridViewCheckBoxCell) row.Cells[0];

instead of

DataGridViewCheckBoxCell chk = e.row.Cell(0);

*EDIT:*I think you really want to do this:

foreach (DataGridViewRow row in dataGridView1.Rows)
{
       DataGridViewCheckBoxCell chk = (DataGridViewCheckBoxCell) row.Cells[0];
       chk.Value = !(chk.Value == null ? false : (bool) chk.Value); //because chk.Value is initialy null
}

    private void setCheckBoxInDataGrid(DataGridView dgv, int pos, bool isChecked)
    {
        for (int i = 0; i < dgv.RowCount; i++)
        {
            dgv.Rows[i].DataGridView[pos, i].Value = isChecked;
        }
    }

This is how I did it