private void btnCategoryAdd_Click(object sender, EventArgs e) { if (txtSupplierName.Text != "") { if (SupplierRepo.checkIfSupplierExists(txtSupplierName.Text)) { MessageBox.Show("Supplier already exists."); } else { double num; bool b = double.TryParse(txtContactNumber.Text, out num); if (b) { SupplierRepo.insert(Guid.NewGuid(), txtSupplierName.Text, txtAddress.Text, double.Parse(txtContactNumber.Text)); fillListView(); clearAll(); MessageBox.Show("Supplier has been added."); } else { MessageBox.Show("Invalid contact number"); } } } else { MessageBox.Show("Supplier name must not be empty"); } }