Numeric only textbox including scientific notation

Hello,

EDIT : if you want to have the final version of the custom control, go to the last post.

For one of my application, I had to restrict some textbox entry to numeric only but I accept scientific notation (so 1E5 is ok) and negative value (so the - sign is ok too) and as some of the users have a config that use coma and others that use dot as decimal separator, I dealt also with that. I wanted also that if you type any non valid key, nothing happen (in appearance ;))

I created 2 functions and worked on the textchanged event.

Function to Check that the text is a number

Code:

---

    Public Function verif_nombre(ByVal text As String) As String
        Dim count As Integer 'To count the number of E
        Dim text_verifie As String = ""
        Dim l As Integer = text.Length
      If l = 0 Then Return text_verifie ' If there is no character, do go further, it is not needed
        Dim charac As Char = text.Chars(text.Length - 1) ' get the last character typed

        If charac = CChar("-") And text.Length = 1 Then ' deal with - sign
            Return text
        End If

        If text.Contains(" ") Then ' replace space by nothing
            text = text.Replace(" ", "")
            Return text
        End If

      'Count the number of e or E in the text
      If text.Contains("e") And text.Contains("E") Then
            count = 2
      ElseIf text.Contains("e") Then
            count = text.Split(CChar("e")).Length - 1
        ElseIf text.Contains("E") Then
            count = text.Split(CChar("E")).Length - 1
        End If

      If count = 1 And (charac = CChar("E") Or charac = CChar("e")) And l > 1 Then 'Deal with the scientific notation
            text_verifie = text
        Else
            If IsNumeric(text) Then ' verify that the text is  numeric
                text_verifie = text
          Else
                text = text.Remove(l - 1) 'if not then remove last charac typed
                text_verifie = text
            End If
        End If
        Return text_verifie
    End Function

---

Manage dot and coma for the number

Code:

---

Public Function gpv(ByVal text As String) As String 'GPV : gère point-virgule = manage dot - coma ;)
                Dim nfi As NumberFormatInfo = NumberFormatInfo.CurrentInfo 'get the info on the decimal separator for the current user
        If nfi.NumberDecimalSeparator = "." Then 'if dot replace all coma by dot
            text = text.Replace(",", ".")
        Else 'if coma replace dot by coma
            text = text.Replace(".", ",")
        End If
      Return text
    End Function

---

Method to manage the TextChanged event

Code:

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Public Sub Numeric_TextBox_TextChanged(sender As Object, e As System.EventArgs)
        Dim TB As TextBox = CType(sender, TextBox)
        TB.Text = verif_nombre(gpv(TB.Text)).ToString
        TB.Select(TB.Text.Length, 0)
    End Sub

---

On the loading of the forms I handle the event for all textbox based on a tag, if the tag = num then I change the event method

Code:

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Private Sub Form_Load(sender As Object, e As System.EventArgs) Handles Me.Load
        For Each TB As TextBox In Me.Controls.OfType(Of TextBox)()
            If TB.Tag Is "num" Then
                AddHandler TB.TextChanged, AddressOf Numeric_TextBox_TextChanged
          End If
        Next
    End Sub

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I would suggest building the functionality into a custom class that inherits TextBox. You would then override the OnTextChanged method rather than handling the TextChanged event. You can then use your custom class directly on your forms instead of a regular TextBox. If you want to see an example of that, follow the CodeBank link in my signature below and check out my own Numeric Text Box thread. You might get some other ideas from that too. For one thing, it's not a great idea to use the TextChanged event for this sort of thing if you can avoid it. That event is raised after the Text property has already changed, so you then have to do bad things like change the Text again in the event handler, as you're doing. Prevention is almost always better than cure, i.e. prevent the Text changing in the first place, if the new value would be invalid.

Thank you for your comments and ideas.

I never did custom class that inherits something so time to learn.
I will have a look to you thread and see how I can improve my code.

Quote:

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Prevention is almost always better than cure

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so I guess, the KeyPress or KeyDown should be better.

A question : When you create a new (user ?) control that inherits, is it possible to put it in the toolbox to be able to use it directly in the design window ? or do I have to call it through the code ?

Regards

Quote:

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Originally Posted by Delaney

so I guess, the KeyPress or KeyDown should be better.

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Generally speaking, yes. In your case though, you have the added complication of having to allow the user to enter the "E" with no guarantee that they'll enter a digit after it, so you'll need some extra validation for that.

Quote:

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Originally Posted by Delaney

A question : When you create a new (user ?) control that inherits, is it possible to put it in the toolbox to be able to use it directly in the design window ? or do I have to call it through the code ?

---

Anything that inherits Control, either directly or indirectly, is a control. A user control is actually something specific. It is a class that inherits UserControl and is used to create a group of child controls that can de used as a unit. For other controls, particularly those inheriting existing standard controls, are generally referred to as custom controls.

Any class declared in your solution that inherits Component (Control inherits Component), either directly or indirectly, will be automatically added a a special group at the top of the Toolbox and can be used in that solution. If you want a custom control available to any solution, declare it in a library project, compile that and put the DLL in an appropriate location. You can then right-click the Toolbox and select Choose Items to select that library and your control. That's how you add any new controls or components to the Toolbox.

Quote:

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Originally Posted by jmcilhinney

Generally speaking, yes. In your case though, you have the added complication of having to allow the user to enter the "E" with no guarantee that they'll enter a digit after it, so you'll need some extra validation for that.
.

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I forgot about this case (too much confidence in my users maybe...), I just tested it and get an error so I will have to correct that.

And thank you for the explanation about user and custom control. :thumb:

regards

Quote:

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Originally Posted by Delaney

too much confidence in my users maybe...

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some User's are as Bad as toothache, the love to-Copy&Paste-
so consider that also

EDIT:
here a few thoughts

Code:

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Public Class Form1

    Private Sub TextBox1_Enter(sender As Object, e As System.EventArgs) Handles TextBox1.Enter
        'to prevent Copy&Paste
        Clipboard.Clear()
    End Sub

    Private Sub TextBox1_KeyPress(sender As Object, e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
        If e.KeyChar = "."c Then
            'allow only one .
            e.Handled = (CType(sender, TextBox).Text.IndexOf("."c) <> -1)
        ElseIf e.KeyChar = "E"c Then
            'allow only one E
            e.Handled = (CType(sender, TextBox).Text.IndexOf("E"c) <> -1)
            'allow Backspace
        ElseIf e.KeyChar <> ControlChars.Back Then
            e.Handled = ("0123456789AaEe".IndexOf(e.KeyChar) = -1)  '<--allowed
        End If
    End Sub

End Class

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I haven't tried what JMC discribes in Post#2, I would need something like that
for a -Date Textbox- and a -Time Textbox- or probably combine those

Here is my update,

I created a custom textbox on the advice of jmcilhinney. That helped me a lot, thanks John. I will be able to put that very easily in all my applications.

I still use the TextChanged event which allows to use copy/paste and will correct it in a very drastic way.
I use also the Leave event, so I can deal with the "E" without a digit after.
I take care also of the use of minus sign as last digit (i.e "12-" recognized by Vb.net as numeric).

So I accept the following : (the number of x is not contractual, you can have more ;) but the number of y is linked to the size of a double)
xxx
xxx.xx or xxx,xx depending of user setting
-xxx
-xxx.xx or -xxx,xxx depending of user setting
xxeyy or xxEyy
xxe-yy or xxE-yy
or any combination of above (no, you can't have xxeEYY )
You cannot leave the textbox if it ends by "e" or "E" (122E for example).

It has been written in VB.net 2010 because I will use it mainly for my work as I have VB 2010 on my office desktop computer.

The files :
Attachment 177417 : the custom control
Attachment 177419 : Example

Regards

Cyril