Why is Windows 10 making this code give an InvalidCastException

Question

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VS2010

The following code snippet works absolutely great when run on Windows 7 professional BUT throws an Invalid Cast Exception when run on Windows 10.
Any idea what Microsoft have changed and what I need to do to get it working on Win10?
It's a friend of mine running it on a Win10 pc & I don't have it on my pc :-)

Many thanks,
Tim

************** Exception Text **************

System.InvalidCastException: Conversion from string "£0.00" to type 'Decimal' is not valid.
   at Microsoft.VisualBasic.CompilerServices.Conversions.ToDecimal(String Value, NumberFormatInfo NumberFormat)
   at Microsoft.VisualBasic.CompilerServices.Conversions.ToDecimal(String Value)
   at GtracsX4.gtac1b.tBox_Validating(Object sender, CancelEventArgs e)

The Code

VB

Private Sub tBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles _
      amtInp.Validating, DescInp.Validating, RefInp.Validating
    Dim mtb As String = sender.tag : Dim mtbx As TextBox = sender : Dim ta As Decimal
    If mtb = "dec" Then
        If (String.IsNullOrEmpty(mtbx.Text)) Then mtbx.Text = "0"
        If IsNumeric(mtbx.Text) = False Then
            msgM = "Only NUMBERS allowed.  Please re-enter"
            msg = New gtzMess(1, "", msgM, "OK", "", "", "S")   '   flags = ISQW
            msg.ShowDialog()
            mtbx.Text = 0
            e.Cancel = True
            Exit Sub
        End If
        ta = CDec(mtbx.Text)
        mtbx.Text = "£" & ta.ToString("N2")
        If mtbx.Name = "amtInp" Then tAmt.Text = CDec(mtbx.Text)
    End If
End Sub

Posted 7-Sep-15 7:50am

Member 11890082

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Comments

Michael_Davies 7-Sep-15 14:45pm

Off the question topic...Why copy the sender.tag to a new variable when all you do is test it = "dec"? Save time and stack just test sender.tag.

Second, why not use the KeyPress event and block non number keys so you never have to verify anything other than empty.

Simple example:

Public Const DecimalStrings As String = ".0123456789" + ChrW(8)

Private Sub DecimalKeyPress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles yourtextbox.KeyPress
'
' Ignore non-numeric keys, allow 0-9 and decimal stop
'
If DecimalStrings.IndexOf(e.KeyChar) = -1 Then
e.Handled = True
ElseIf e.KeyChar = "." Then
'
' If there already is a decimal stop in the box ignore duplicates
'
If CType(sender, TextBox).Text.IndexOf(".") <> -1 Then
e.Handled = True
End If
End If

If e.KeyChar = ChrW(13) Then
Me.SelectNextControl(sender, True, True, True, True)
End If

etc.

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OriginalGriff · Answer 1 · 2015-09-07T08:08:00

Why are you doing that?
Look at your code:

VB

ta = CDec(mtbx.Text)
mtbx.Text = "£" & ta.ToString("N2")
If mtbx.Name = "amtInp" Then tAmt.Text = CDec(mtbx.Text)

VB

ta = CDec(mtbx.Text)

Take a Textbox value, and convert it to a Decimal. This is a poor idea: you should be using Decimal.TryParse and reporting problems to the user.

VB

mtbx.Text = "£" & ta.ToString("N2")

Having converted it to a decimal value, you immediately convert it back to a tring, and tack a currency symbol on the front.

VB

If mtbx.Name = "amtInp" Then tAmt.Text = CDec(mtbx.Text)

You then convert that back to a decimal (which will throw away the currency, if it doesn't cause it to fail, which it does) in order to convert it back into a string, to put it in a textbox.

That's...um...very odd.
Use TryParse to convert it (with reporting), and look at what you are trying to store where - you should need at most two type conversions: one to a dec, and one to a string. And that's only because your specify a format for the string value!
And your problem will go away at the same time.

Sergey Alexandrovich Kryukov · Answer 2 · 2015-09-07T08:15:00

It is not related to Windows version, it's related to the different default culture set up in two different cases you described. Your code should either be culture-neutral, or you have to force certain fixed culture in the application itself, which is a per-thread option:
https://msdn.microsoft.com/en-us/library/system.threading.thread.currentculture(v=vs.110).aspx[^],
https://msdn.microsoft.com/en-us/library/system.threading.thread.currentuiculture(v=vs.110).aspx[^].

—SA

Why is Windows 10 making this code give an InvalidCastException

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