private void add_Click(object sender, EventArgs e)
 {
     ReceiptAdd receiptAdd = new ReceiptAdd();
     reset();
     receiptAdd.Show();
     this.Visible = false;
 }
 private void btnPayment_Click(object sender, EventArgs e)
 {
     ReceiptAdd receipt = new ReceiptAdd(txtContractId.Text, txtCustomerName.Text, "", txtRest.Text, "Kí hợp đồng thuê nhà");
     receipt.Show();
 }