Question

The Murach's Visual Basic 2015 Book And Visual Studio

Exercise 7-2 Enhance the Invoice Total application

If you did exercise 6-1 in the last chapter, this exercise asks you to add data validation and exception handling to it.

1. Copy the Invoice Total application from your C:\VB 2015\Chapter 06 directory to your Chapter 07 directory. This should be your solution to exercise 6-1 of the last chapter.

2. If your application has both a Sub procedure and a Function procedure for setting the discount percent, delete the Sub procedure.

3. Go to the Sub procedure for setting the discount percent and comment out the Else clause. That means that a discount percent is only set for customer type codes of R and C, so assume that these are the only valid customer type codes.

4. Add data validation for the customer type entry so it has to be either R or C. To do that, write a Function procedure named IsValidCustomerType that validates the entry, displays an error message if the entry is invalid, and returns a Boolean value that indicates whether the type is valid.

5. Call the IsValidCustomerType function at the start of the btnCalculate_Click procedure, and exit from the procedure if the customer type is invalid. Then, test this change.

Public Class frmInvoiceTotal

Private Sub btnCalculate_Click(sender As Object,
e As EventArgs) Handles btnCalculate.Click

Dim subtotal As Decimal = CDec(txtSubtotal.Text)
Dim discountPercent As Decimal

Me.GetDiscountPercent(txtCustomerType.Text, subtotal, discountPercent)
Dim discountAmount As Decimal = subtotal * discountPercent
Dim invoiceTotal As Decimal = subtotal - discountAmount

txtDiscountPercent.Text = FormatPercent(discountPercent, 1)
txtDiscountAmount.Text = FormatCurrency(discountAmount)
txtTotal.Text = FormatCurrency(invoiceTotal)

txtCustomerType.Select()
End Sub

Private Sub GetDiscountPercent(customerType As String, subtotal As Decimal,
ByRef discountPercent As Decimal)
If customerType = "R" Then
If subtotal < 100 Then
discountPercent = 0
ElseIf subtotal >= 100 AndAlso subtotal < 250 Then
discountPercent = 0.1D
ElseIf subtotal >= 250 Then
discountPercent = 0.25D
End If
ElseIf customerType = "C" Then
If subtotal < 250 Then
discountPercent = 0.2D
Else
discountPercent = 0.3D
End If
Else
discountPercent = 0.4D
End If
End Sub

Private Sub btnExit_Click(sender As Object,
e As EventArgs) Handles btnExit.Click
Me.Close()
End Sub

Private Sub ClearResultBoxes(sender As Object,
e As EventArgs) _
Handles txtCustomerType.TextChanged, txtSubtotal.TextChanged
txtDiscountPercent.Text = ""
txtDiscountAmount.Text = ""
txtTotal.Text = ""
End Sub
End Class

Answer 1

Public Class Form1

Private Sub btnCalculate_Click(sender As Object,
e As EventArgs) Handles btnCalculate.Click

Dim subtotal As Decimal = CDec(txtSubtotal.Text)
Dim discountPercent As Decimal

Me.GetDiscountPercent(txtCustomerType.Text, subtotal, discountPercent)
Dim discountAmount As Decimal = subtotal * discountPercent
Dim invoiceTotal As Decimal = subtotal - discountAmount

txtDiscountPercent.Text = FormatPercent(discountPercent, 1)
txtDiscountAmount.Text = FormatCurrency(discountAmount)
txtTotal.Text = FormatCurrency(invoiceTotal)

txtCustomerType.Select()
End Sub

Private Sub GetDiscountPercent(customerType As String, subtotal As Decimal, ByRef discountPercent As Decimal)
If customerType = "R" Then
If subtotal < 100 Then
discountPercent = 0
ElseIf subtotal >= 100 AndAlso subtotal < 250 Then
discountPercent = 0.1D
ElseIf subtotal >= 250 Then
discountPercent = 0.25D
End If
ElseIf customerType = "C" Then
If subtotal < 250 Then
discountPercent = 0.2D
Else
discountPercent = 0.3D
End If
Else
discountPercent = 0.4D
End If
End Sub

Private Sub btnExit_Click(sender As Object,
e As EventArgs) Handles btnExit.Click
Me.Close()
End Sub

Private Sub ClearResultBoxes(sender As Object, e As EventArgs) Handles txtSubtotal.TextChanged
txtDiscountPercent.Text = ""
txtDiscountAmount.Text = ""
txtTotal.Text = ""
End Sub
Private Function IsValidCustomerType() _
As Boolean
If IsValidCustomerType = "R" Then
MessageBox.Show("Customer Type has to be R or C or T", "Entry Error")
txtCustomerType.Select()
Return False
Else
Return True
End If
If Not IsValidCustomerType = "C" Then
MessageBox.Show("Customer Type has to be R or C or T", "Entry Error")
txtCustomerType.Select()
Return False
Else
Return True
End If

End Function
End Class

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