Another way on how to restrict the textbox to accept only alpha or numeric characters

lotus18 · #1 December 6th, 2008, 10:46 AM

Hello World!

I have a sample code here written in vb .net that restricts the textbox to accept only alpha, alphanumeric or numeric characters.

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Public Enum MyOption

        Alpha = 1

        AlphaNumeric = 2

        Numeric = 3

    End Enum
 
 Public Sub SetCharacter(ByVal CharacterOption As MyOption, _

ByVal kp As KeyPressEventArgs)

        Select Case CharacterOption

            Case MyOptions.Alpha

                If Not ( _

                    kp.KeyChar Like "[A-Z]" Or _

                    kp.KeyChar Like "[a-z]" Or _

                    kp.KeyChar = vbBack Or _

                    Asc(kp.KeyChar) = 32) Then

                    kp.KeyChar = vbNullChar

                End If

            Case MyOptions.AlphaNumeric

                If Not ( _

                        kp.KeyChar Like "[A-Z]" Or _

                        kp.KeyChar Like "[a-z]" Or _

                        kp.KeyChar Like "[ñÑ]" Or _

                        kp.KeyChar Like "[0-9]" Or _

                        kp.KeyChar = vbBack Or _

                        Asc(kp.KeyChar) = 32) Then

                    kp.KeyChar = vbNullChar

                End If

            Case MyOptions.Numeric

                If Not ( _

                     kp.KeyChar Like "[0-9]" Or _

                     kp.KeyChar = vbBack Or _

                     Asc(kp.KeyChar) = 32) Then

                    kp.KeyChar = vbNullChar

                End If

        End Select
 
    End Sub

Just place the SetCharacter method to the KeyPress event of a textbox, combobox, etc.

Sample 1. A textbox that accepts only numeric characters

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 Private Sub Text1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles Text1.KeyPress

        SetCharacter(MyOption.Numeric, e)

    End Sub

As you noticed, the SetCharacter method has 2 parameters-CharacterOption and kp.

CharacterOption - Sets the MyOption value whether you want alpha, alphanumeric, or numeric
kp - Gets the current key that you have pressed.

Rey Sean
Mabuhay ang pinoy : )

Montravont · #2 December 8th, 2008, 05:50 PM

My first thought was... Why? Then I read the end of it and it changed to Oh!.

Nice, work. Personally I don't tend to need to limit things to alpha or alphanumeric, only numeric. In those cases, if that's the only thing I need to limit on keypress, I'll just write the numeric limiting code once and refer all the keypresses to that one bit of code.

This is pretty friggin nifty though.

madankarmukta · #3 December 9th, 2008, 09:06 AM

HI,

Make use of Regular Expressiona.

Thanks!

balabaster · #4 December 9th, 2008, 10:00 PM

Your code is a great idea and very useful...however, I thought it might be a bit more extensible in this format, it's also easier to write unit tests for:

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 Public Enum Options

  Alpha

  AlphaNumeric

  Numeric

End Enum
 
Function Pattern(ByVal CharOpt As Options)
 
  Dim s = String.Empty

  Select Case CharOpt

      Case Options.Alpha

          s = "A-Za-z"

      Case Options.AlphaNumeric

          s = "\w"

      Case Options.Numeric

          s = "\d"

  End Select
 
  'All my patterns allow spaces... 

  Return String.Format("[{0}\s]", s)
 
End Function
 
Public Sub AllowChars(ByVal CharOpt As Options, _

                      ByVal kp As KeyPressEventArgs)
 
  'Create list of always allowable keys

  Dim Allow As Keys() = {Keys.Delete, Keys.Back}
 
  'If not one of the allowable keys we predefined, 

  'then check the characters entered against the 

  'pattern defined for the selected pattern option, 

  'if it doesn't match, then ditch it...

  If Not Allow.Contains(AscW(kp.KeyChar)) Then

    If Not Regex.IsMatch(kp.KeyChar, Pattern(CharOpt)) Then

      kp.KeyChar = ControlChars.NullChar

    End If

  End If
 
End Sub
 
Private Sub KeyPressed(ByVal sender As Object, _

                       ByVal e As KeyPressEventArgs) _

  Handles tb1.KeyPress
 
  AllowChars(Options.Numeric, e)
 
End Sub

lotus18 · #5 December 10th, 2008, 12:31 AM

I will take your comments as complements. Anyway, thank you guys for your comments : )

To madankarmukta, I was thinking about RegularExpressions and I know this is more appropriate and more acceptable than mine LOL. I found a lot of tutorials in the net using this and as you can see in the title "Another way on how ...", so I created another way on how to handle this.

Rey Sean

Another way on how to restrict the textbox to accept only alpha or numeric characters

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