VB Entering a Non_Numeric value crashes the program - vba

Question

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Public Class Form1
Private Sub BtnCalculateRevenue_Click(sender As Object, e As EventArgs) Handles BtnCalculateRevenue.Click
Dim intvalue As Integer = CInt(TxtInputClassA.Text)
Dim intvalue2 As Integer = CInt(TxtInputClassB.Text)
Dim intvalue3 As Integer = CInt(TxtinputClassC.Text)
Dim total As Double
Try
LblStatus.Text = String.Empty
LblClassAResult.Text = (intvalue * 15).ToString("c")
LblClassBResult.Text = (intvalue2 * 12).ToString("c")
LblClassCResult.Text = (intvalue3 * 9).ToString("c")
total = CDbl((intvalue * 15) + (intvalue2 * 12) + (intvalue3 * 9))
LblTotal.Text = total.ToString("c")
Catch
LblStatus.Text = "Please Enter a Number"
End Try
End Sub
Private Sub BtnExit_Click(sender As Object, e As EventArgs) Handles BtnExit.Click
Me.Close()
End Sub
Private Sub BtnClear_Click(sender As Object, e As EventArgs) Handles BtnClear.Click
TxtInputClassA.Clear()
TxtInputClassB.Clear()
TxtinputClassC.Clear()
LblClassAResult.Text = String.Empty
LblClassBResult.Text = String.Empty
LblClassCResult.Text = String.Empty
LblTotal.Text = String.Empty
End Sub
End Class
VB Entering a Non_Numeric value crashes the program

Answer 1

Validation is built right into Windows Forms so you should make use of it. If you want to force the user to enter numbers in each of three TextBoxes then you can do this:
Private Sub TextBoxes_Validating(sender As Object, e As ComponentModel.CancelEventArgs) Handles TextBox3.Validating, TextBox2.Validating, TextBox1.Validating
Dim tb = DirectCast(sender, TextBox)
If Not Integer.TryParse(tb.Text, Nothing) Then
'Select all the invalid text and highlight it.
tb.SelectAll()
tb.HideSelection = False
MessageBox.Show("Please enter a whole number",
"Invalid Input",
MessageBoxButtons.OK,
MessageBoxIcon.Exclamation)
'Remove highlight when TextBox is not focused.
tb.HideSelection = True
'Don't let the control lose focus while data is invalid.
e.Cancel = True
End If
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If ValidateChildren() Then
'All data is valid so proceed.
Dim n1 = CInt(TextBox1.Text)
Dim n2 = CInt(TextBox2.Text)
Dim n3 = CInt(TextBox3.Text)
'...
End If
End Sub
The ValidateChildren method will raise the Validating event for every control on the form and return False if any fail validation, i.e. e.Cancel is set to True in any event handlers, so that ensures that even controls that never received focus will be validated before the data is used.

Answer 2

Its bombing out on your cast "CInt(*value*)" so you can fix the code a couple ways. You can move your try above the casts like...
Try
Dim intvalue As Integer = CInt(TxtInputClassA.Text)
Dim intvalue2 As Integer = CInt(TxtInputClassB.Text)
Dim intvalue3 As Integer = CInt(TxtinputClassC.Text)
Dim total As Double
LblStatus.Text = String.Empty
You can do a data validation on your inputs and exit if they aren't all numeric (put this above your Dim intvalue code)
For Each value As String In {TxtInputClassA.Text, TxtInputClassA.Text, TxtInputClassA.Text}
If Not IsNumeric(TxtInputClassA.Text) Then
LblStatus.Text = "Please Enter a Number"
Exit Sub
End If
Next
Instead of casting as an int, use the tryparse method on Int32...
Dim intvalue As Integer
If Not Int32.TryParse(TxtInputClassA.Text, intvalue) Then
Exit Sub
End If
Or you could intercept the keypresses on each text box so that only numbers can be entered
Private Sub TxtInputClassA_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TxtInputClassA.KeyPress
If Not Char.IsDigit(e.KeyChar) Then
e.Handled = True
End If
End Sub
You can make that routine universal and append the event handler for all three text boxes like...
Private Sub EnforceOnlyNumericKeyPresses(sender As Object, e As KeyPressEventArgs) Handles TxtInputClassA.KeyPress, TxtInputClassB.KeyPress, TxtInputClassC.KeyPress
If Not Char.IsDigit(e.KeyChar) Then
e.Handled = True
End If
End Sub
Choose your favorite or do all of them, lots of choices.

Answer 3

Replace your textboxes with NumericUpDown controls and retrieve their .Value for your calculation. NUDs don't allow non numeric input and can have a fixed number of decimal places which may also be useful in a financial context