Length Validation for all Multiline Textboxes on a Page

Imports Microsoft.VisualBasic
Imports System
Imports System.Data
Imports System.Configuration
Imports System.Web
Imports System.Web.Security
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls

' Created by Sina Falahati on 29.10.2006 07:39
' With thanks to:
' Abaif for his JSHelper CheckTextAreaMaxLength sample
' A. Kluge for his Textarea-Counter
' http://www.codeproject.com/KB/aspnet/MultilineLengthValidator.aspx?msg=2718271#xx2718271xx

'/ <summary>
'/ Description:
'/ If you specify TextMode="SingleLine" on a TextBox, it generates an html <input> box with a
'/ MaxLength attribute. If you specify TextMode="MultiLine", it generates an html <textarea>
'/ box ... and doesn't set the MaxLength attribute, since it's undefined for <textarea> elements.
'/ This will add a check onKeyUp for the textarea that will prevent too many
'/ characters from being entered. Set the MaxLength as normal as a property of the TextBox and then call
'/ this method to generate JavaScript to do the client-side checks.
'/
'/ How to use:
'/ For performing length validation on all multiline Text-Boxes on a page: Put "CheckAllMaxLengthsWithinParentControl(this);" inside the page's Page_Load function
'/ For performing length validation on a specific Text-Box: Put "CheckMaxLength(theTextBox);" inside the page's Page_Load function
'/ For FormViews inside ATLAS Update-Panels use FormView's OnItemCreated event with CheckAllMaxLengthsWithinParentControl((FormView)sender);
'/ </summary>
' Converted to vb.net (but no tested) by Jim Engebretson

Public Class TextAreaValidator

  Public Shared Sub CheckAllMaxLengthsWithinParentControl(ByVal oParent As System.Web.UI.Control)

	 Dim oChild As Control = Nothing
	 Dim oChildTextBox As TextBox = Nothing

	 If ((oParent Is Nothing) Or (Not oParent.HasControls())) Then
		Return
	 End If

	 Dim iItem As Integer
	 For iItem = 0 To oParent.Controls.Count - 1 Step iItem + 1
		oChild = oParent.Controls(iItem)
		If (Not oChild.Visible) Then
		   Continue For
		End If

		If (oChild.Controls.Count > 0) Then
		   CheckAllMaxLengthsWithinParentControl(oChild) ' iterate through child-controls
		   If oChild.GetType.ToString = "System.Web.UI.WebControls.TextBox" Then
			  ' If (ct = System.Web.UI.WebControls.TextBox) Then
			  oChildTextBox = CType(oChild, TextBox)
			  ' Change TextBox Properties Here
			  ' only Multiline Text-Boxes need this
			  If (oChildTextBox.TextMode = TextBoxMode.MultiLine And oChildTextBox.MaxLength <> 0) Then ' 0 == no limit
				 CheckMaxLength(oChildTextBox)
			  End If
		   End If
		End If
	 Next
  End Sub

  Public Shared Sub CheckMaxLength(ByVal textArea As System.Web.UI.WebControls.TextBox)
	 textArea.Attributes.Add("onKeyUp", _
	 "CheckMaxLength(event," & _
	 "'" & textArea.ClientID & "'," & _
	 textArea.MaxLength & ");")

	 textArea.Attributes.Add("onChange", _
	 "CheckMaxLength(event," & _
	 "'" & textArea.ClientID & "'," & _
	 textArea.MaxLength & ");")

	 RegisterCheckMaxLength(textArea.Page)
  End Sub

  Private Shared Sub RegisterCheckMaxLength(ByRef page)
	 Dim script As String = String.Empty

	 'Build the function block
	 script = "function CheckMaxLength(e, textarea_id, max) {" & vbCrLf
	 script += "var theTextArea = document.getElementById(textarea_id);" & vbCrLf
	 script += "if (!e.which) keyCode = event.keyCode; // ie5+ op5+" & vbCrLf
	 script += "else keyCode = e.which; // nn6+" & vbCrLf
	 script += "if (theTextArea.value.length>max)" & vbCrLf
	 script += "{" & vbCrLf
	 script += "theTextArea.value = theTextArea.value.substring(0,max); " & vbCrLf
	 script += "}" & vbCrLf
	 script += "};" & vbCrLf

	 'Enclose function <script> tags and register at top of page
	 'Check whether they are already registered
	 If (Not page.IsClientScriptBlockRegistered("CheckMaxLength")) Then
		'Register the script
		page.RegisterClientScriptBlock("CheckMaxLength", EncloseScriptBlock(script))
	 End If
  End Sub


  Private Shared Function EncloseScriptBlock(ByVal script) As String
	 script = "<script type='text/javascript'>" & vbCrLf & _
	 "<!--" & vbCrLf & _
	 script & vbCrLf & _
	 "// -->" & vbCrLf & _
	 "</script>"
	 Return script
  End Function

End Class