validating negative values

Question

I have a function that allows a user to enter numeric vallues and also a period for the decimal points but I also want to allow for users to enter the minus sign to allow users to enter negative values . How would I go about it.

 Public Function SingleDecimal(ByVal sender As System.Object, ByVal eChar As Char) As Boolean
        Dim chkstr As String = "0123456789."
        If chkstr.IndexOf(eChar) > -1 OrElse eChar = vbBack Then
            If eChar = "." Then

                If CType(sender, Telerik.WinControls.UI.RadTextBox).Text.IndexOf(eChar) > -1 Then
                    Return True
                Else
                    Return False
                End If

            End If

            Return False
        Else
            Return True
        End If
    End Function

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If you think it you can achieve it

Answer 1

Public Class NumericTextBox
    Inherits TextBox
    Private SpaceOK As Boolean = False

    ' Restricts the entry of characters to digits (including hex),
    ' the negative sign, the e decimal point, and editing keystrokes (backspace).
    Protected Overrides Sub OnKeyPress(ByVal e As KeyPressEventArgs)
        MyBase.OnKeyPress(e)

        Dim numberFormatInfo As System.Globalization.NumberFormatInfo = System.Globalization.CultureInfo.CurrentCulture.NumberFormat
        Dim decimalSeparator As String = numberFormatInfo.NumberDecimalSeparator
        Dim groupSeparator As String = numberFormatInfo.NumberGroupSeparator
        Dim negativeSign As String = numberFormatInfo.NegativeSign

        Dim keyInput As String = e.KeyChar.ToString()

        If [Char].IsDigit(e.KeyChar) Then
            ' Digits are OK
        ElseIf keyInput.Equals(decimalSeparator) OrElse keyInput.Equals(groupSeparator) OrElse keyInput.Equals(negativeSign) Then
            ' Decimal separator is OK
        ElseIf e.KeyChar = vbBack Then
            ' Backspace key is OK
            '    else if ((ModifierKeys & (Keys.Control | Keys.Alt)) != 0)
            '    {
            '     // Let the edit control handle control and alt key combinations
            '    }
        ElseIf Me.SpaceOK AndAlso e.KeyChar = " "c Then

        Else
            ' Swallow this invalid key and beep
            e.Handled = True
        End If

    End Sub


    Public ReadOnly Property IntValue() As Integer
        Get
            Return Int32.Parse(Me.Text)
        End Get
    End Property


    Public ReadOnly Property DecimalValue() As Decimal
        Get
            Return [Decimal].Parse(Me.Text)
        End Get
    End Property


    Public Property AllowSpace() As Boolean

        Get
            Return Me.SpaceOK
        End Get
        Set(ByVal value As Boolean)
            Me.SpaceOK = value
        End Set
    End Property
End Class

Example from: http://msdn.microsoft.com/en-us/library/ms229644%28v=vs.80%29.aspx

Answer 2

I have a function that allows a user to enter numeric vallues and also a period for the decimal points but I also want to allow for users to enter the minus sign to allow users to enter negative values . How would I go about it.

I wouldn't do it that way at all. In my opinion - of course do keep that caveat in mind - it's not worth the hassle of trying to make your control work that way and even if you do - I bet you'll miss something.

Let them type in anything they want - no matter what it is. Then use the control's .Validating event to test for it and if it fails the test, set e.Cancel to true, show them a message, and force them to go back and change it.

Again ... in my opinion.

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Please call me Frank :)

Answer 3

I have a function that allows a user to enter numeric vallues and also a period for the decimal points but I also want to allow for users to enter the minus sign to allow users to enter negative values . How would I go about it.

I wouldn't do it that way at all. In my opinion - of course do keep that caveat in mind - it's not worth the hassle of trying to make your control work that way and even if you do - I bet you'll miss something.

Let them type in anything they want - no matter what it is. Then use the control's .Validating event to test for it and if it fails the test, set e.Cancel to true, show them a message, and force them to go back and change it.

Again ... in my opinion.

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Please call me Frank :)

Task can be implemented on 100 ways...

In linked example OP can see how to implement validation using System.Globalization.NumberFormatInfo. 

Answer 4

You are already accepting "3.45.21.456" as valid input... definately not a valid single value....

I see you are using a non-standard text box so perhaps it is internally limiting the ways in which text can be entered, but typically it isn't feasible to account for all ways in which a value might be entered into a textbox.

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Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 5

Maybe OP work on some specific application like calculator.

Answer 6

Task can be implemented on 100 ways...

In linked example OP can see how to implement validation using System.Globalization.NumberFormatInfo. 

Well once again, you and I have a difference of opinion. Variety is the spice of life though, so as they say "to each their own".

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Please call me Frank :)

Answer 7

Task can be implemented on 100 ways...

In linked example OP can see how to implement validation using System.Globalization.NumberFormatInfo. 

Well once again, you and I have a difference of opinion. Variety is the spice of life though, so as they say "to each their own".

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Please call me Frank :)

It's not difference in opinion... We don't know why OP needs validation. If OP work on some application like calculator, game etc.. than validation should be implemented in OnKeyDown event handler. If he work on some business application than validation can be implemented in OnValidating event. OP also can combine validations and show some tooltip/baloon from OnKeyDown  even handler but allow user to type anything and to show error message from OnValidating event handler.

Answer 8

It's not difference in opinion...

Everything that you said following that isn't germane. I didn't and won't say that it's not accurate but what IS germane is that clearly you feel "threatened" by someone else saying anything which in any way might make YOUR answer look incorrect.

For the record here and to put a quick end to this banter, I have NO doubts of your knowledge, skill, deftness, and ability with this; you have proven that time and time again and I have no reservations in saying that you can run circles around me.

That said, I stated what I BELIEVE TO BE ACCURATE AND CORRECT - as did you.

Now let's leave it to the OP.

Please...

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Please call me Frank :)

Answer 9

This would take care of the Keyboard

 Private Sub TextBox1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox1.KeyDown
        Dim ValidKey() As Keys = {Keys.OemMinus, Keys.OemPeriod, Keys.Decimal, Keys.Subtract}
        If Not e.KeyCode = Keys.Back Then
            If Char.IsDigit(Chr(e.KeyValue)) OrElse ValidKey.Contains(e.KeyData) Then
                Dim KV As Integer = e.KeyValue
                If e.KeyValue > 108 Then KV -= 64
                If e.KeyValue > 124 Then KV -= 80
                If (KV = 45 AndAlso TextBox1.Text = "") Then
                    Exit Sub
                ElseIf (KV = 45 AndAlso Not TextBox1.Text = "") Then
                    e.SuppressKeyPress = True
                End If
                If Not IsNumeric(TextBox1.Text & Chr(KV)) Then
                    e.SuppressKeyPress = True
                End If
            Else
                e.SuppressKeyPress = True
            End If
        End If
    End Sub

And this take care of the "Paste"

Private Sub TextBox1_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
        If Not IsNumeric(TextBox1.Text) Then TextBox1.Text = ""
    End Sub

Answer 10

Another method:

    Function TestDecimal(StrIn As String) As Boolean
        Dim DummyDec As Decimal = 0
        Return Decimal.TryParse(StrIn, DummyDec)
    End Function

Answer 11

Another method:

    Function TestDecimal(StrIn As String) As Boolean
        Dim DummyDec As Decimal = 0
        Return Decimal.TryParse(StrIn, DummyDec)
    End Function

Devon,

You're not stating where/how to use that function but that aside, do be aware that the .TryParse method will set the decimal to zero if it fails. So what if the user actually entered zero? How would you be able to know?

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Please call me Frank :)

Answer 12

Devon,

You're not stating where/how to use that function but that aside, do be aware that the .TryParse method will set the decimal to zero if it fails. So what if the user actually entered zero? How would you be able to know?

By not ignoring the function return value. :-)

However, instead of calling TestDecimal, one can simply directly call

   if decimal.tryparse(str, 0) then

   end if

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Armin

Answer 13

By not ignoring the function return value. :-)

However, instead of calling TestDecimal, one can simply directly call

   if decimal.tryparse(str, 0) then

   end if

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Armin

Right - and in the other example that I showed the OP this week, I have that (more or less) in the .Validating event.

Armin! Dang man - you've been hiding ... good to see you around again. :)

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Please call me Frank :)

Answer 14

Frank:

The return from Decimal.TryParse is Boolean

Answer 15

Frank:

The return from Decimal.TryParse is Boolean

Oh I did miss that didn't I *LOL*

That's what I've used in sample code that I used in the .Validating event that I showed earlier this week to the same OP. I use an ErrorProvider but really any means of communicating the fact that it's not acceptable (a MessageBox even, but I think that's annoying).

By putting it in the .Validating event, we have the option to "trap" the user into the control, thereby forcing them to change it. Normally I test that it's not String.Empty; if it is then it doesn't test it (but it won't accept it, it just allows the user to continue without being stuck) and I show in the EP that if they want to continue, they need to either provide a valid entry or clear it all together.

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Please call me Frank :)

Answer 16

Hello Tendemaire,

I don't see it in this thread, but Visual Basic has already long time (from VB1 to VB11) the function 

If Isnumeric(TextBox1.Text) then 

It test all possible numeric values which can exist on a system even the exponent ones.

Be aware to speak with Herfried E. Wagner that you should not rely on this for key-presses or things like that, the end user can past in values in a textbox, 

:-)

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Success
Cor

Answer 17

Armin! Dang man - you've been hiding ... good to see you around again. :)

Hi Frank,

good to see you too. :)

A while ago, it became a kind of overkill, so I (temporarily) quitted participation. Moreover, the usage of these forums is so laborious and time consuming that I didn't want to do it to me anymore. Unfortunatelly nothing changed in the meantime. :-(

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Armin

Answer 18

good to see you too. :)

A while ago, it became a kind of overkill, so I (temporarily) quitted participation. Moreover, the usage of these forums is so laborious and time consuming that I didn't want to do it to me anymore. Unfortunatelly nothing changed in the meantime. :-(

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Armin

I understand! :)

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Please call me Frank :)