Using If Staments for accepting Alphanumeric data in Textboxes only

Question

Good Afternoon Sir and Madam

Can You help me find an If statement command that only accepts Alphanumeric data in textboxes In Visual Basic 2015 Express?  Thank You.

Sincerely Yours,

James Delorn Howland Jr.

Answer 1

Can You help me find an If statement command that only accepts Alphanumeric data in textboxes In Visual Basic 2015 Express?

The usual procedure would be to iterate over the characters in the string and test for a numeric range of ASCII values.  That may fail for certain encodings.

For Each c As Char In TextBox1.Text
    If AscW(c) < 48 OrElse (AscW(c) > 57 AndAlso AscW(c) < 65) OrElse (AscW(c) > 90 AndAlso AscW(c) < 97) OrElse AscW(c) > 122 Then
        MsgBox("Invalid")
        Exit For
    End If
Next

Answer 2

For each c as Char in TextBox1.Text
   If Char.IsLetterOrDigit(c) then ........

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Lloyd Sheen

Answer 3

You can also use a Regular Expressions filter:

        Dim AlphaNumText As New System.Text.RegularExpressions.Regex("^[a-zA-Z0-9]*$")
        If Not AlphaNumText.IsMatch(AlphaNumTextBox.Text) Then
            MsgBox("Invalid alphanumeric text")
        End If

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Paul ~~~~ Microsoft MVP (Visual Basic)

Answer 4

Hello,

Another idea is to encapsulate the logic into a custom TextBox e.g.

Imports System.Text.RegularExpressions
Public Class AlphaNumericTextBox
    Inherits TextBox
    Protected Overrides Sub OnTextChanged(e As EventArgs)
        MyBase.OnTextChanged(e)
        Dim charsFromEnd = Text.Length - SelectionStart
        Text = Regex.Replace(Text, "\W", "", RegexOptions.None)
        SelectionStart = Text.Length - charsFromEnd
    End Sub
End Class

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Answer 5

Good Afternoon Sir and Madam

Can You help me find an If statement command that only accepts Alphanumeric data in textboxes In Visual Basic 2015 Express?  Thank You.

Sincerely Yours,

James Delorn Howland Jr.

This code uses some If logic to only allow Alphanumeric data to be entered into a TextBox. Pasting can not be used with the TextBox.

On the other hand Visual Studio 2015 Community edition is free and provides more capability than Express editions although I can't find a Visual Studio 2015 Express edition or Visual Basic 2015 Express edition.

Option Strict On

Public Class Form1

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.Location = New Point(CInt((Screen.PrimaryScreen.WorkingArea.Width / 2) - (Me.Width / 2)), CInt((Screen.PrimaryScreen.WorkingArea.Height / 2) - (Me.Height / 2)))
    End Sub

    Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
        If Char.IsPunctuation(e.KeyChar) Or Char.IsSymbol(e.KeyChar) Then 'Allows only Alphanumeric and some keys like delete, backspace, enter, etc in TextBox1
            e.Handled = True
        End If
    End Sub

    Private Sub TextBox1_KeyDown(sender As Object, e As KeyEventArgs) Handles TextBox1.KeyDown
        If e.Control AndAlso e.KeyCode = Keys.V Then e.SuppressKeyPress = True 'Disallows paste into TextBox1
    End Sub

End Class

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La vida loca

Answer 6

Hi James,

Thank you for posting in MSDN Forum.

If you assign true to the value of the property Handle of the event arguments, the cancellation of the event will cause unwanted to be ignored. Please check and refer the following code snippet:

Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
        Dim ch As Char = e.KeyChar
        If Not ch.IsLetter(ch) And Not ch.IsNumber(ch) Then
            ' Kill the entered character
            e.Handled = True
        End If

    End Sub

For more information you could refer that:

https://msdn.microsoft.com/en-us/library/system.char.isletter.aspx

http://msdn.microsoft.com/en-us/library/system.char.isdigit.aspx

Best Regards,

Neda Zhang

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