//Trigger event when selecting a drop-down box private void cboBookTypeOne_SelectedValueChanged(object sender, EventArgs e) { //Determine if the options in the correct selection if (cboBookTypeOne.SelectedValue == null) { return; } else if (!ValidateInput.IsInteger(cboBookTypeOne.SelectedValue.ToString())) { return; } else { //Determine if there are no level two options, if any, enable, load data in the database, no, remain disabled if (objBookTypeServices.IsExistSubType(Convert.ToInt32(cboBookTypeOne.SelectedValue.ToString()))) { //Enable subclass drop-down box cboBookTypeTwo.Enabled = true; //Load LoadSubTypeInfo(Convert.ToInt32(cboBookTypeOne.SelectedValue.ToString())); } else { //Disable Subclass drop-down box cboBookTypeTwo.Enabled = false; cboBookTypeTwo.Text = "No secondary class"; } //Generate numbers lblBookId.Text = objBookServices.BuildNewBookId(Convert.ToInt32(cboBookTypeOne.SelectedValue.ToString())); } }