private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            if (dataGridView1.Columns[e.ColumnIndex] is DataGridViewCheckBoxColumn)
            {
                bool state = Convert.ToBoolean(((DataGridViewCheckBoxCell)dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex]).EditingCellFormattedValue);
                foreach (DataGridViewRow dgvr in dataGridView1.Rows)
                {
                    ((DataGridViewCheckBoxCell)dgvr.Cells[e.ColumnIndex]).Value = state;
                }
            }
        }