Specifying maxlength for multiline textbox

Question

I m trying to use asp    lt asp TextBox ID  txtInput  runat  server  TextMode  MultiLine  gt  lt  asp TextBox gt    I want a way to specify the maxlength property  but apparently there s no way possible for a multiline textbox  I ve been trying to use some JavaScript for the onkeypress event    onkeypress  return textboxMultilineMaxNumber this maxlength    function textboxMultilineMaxNumber txt  maxLen        try           if  txt value length  gt   maxLen - 1   return false        catch  e          return true      While working fine the problem with this JavaScript function is that after writing characters it doesn t allow you to delete and substitute any of them  that behavior is not desired   Have you got any idea what could I possibly change in the above code to avoid that or any other ways to get round it

User · Answer

Nearly all modern browsers now support the use of the maxlength attribute for textarea elements.(https://caniuse.com/#feat=maxlength)

To include the maxlength attribute on a multiline TextBox, you can simply modify the Attributes collection in the code behind like so:

txtTextBox.Attributes["maxlength"] = "100";

If you don't want to have to use the code behind to specify that, you can just create a custom control that derives from TextBox:

public class Textarea : TextBox
{
    public override TextBoxMode TextMode
    {
        get { return TextBoxMode.MultiLine; }
        set { }
    }

    protected override void OnPreRender(EventArgs e)
    {
        if (TextMode == TextBoxMode.MultiLine && MaxLength != 0)
        {
            Attributes["maxlength"] = MaxLength.ToString();
        }

        base.OnPreRender(e);
    }
}

User · Answer

This snippet worked in my case  I was searching for the solution and thought to write this so that it may help any future reader    ASP   lt asp TextBox ID  tbName  runat  server  MaxLength  250  TextMode  MultiLine  onkeyUp  return CheckMaxCount this event 250    gt  lt  asp TextBox gt    Java Script  function CheckMaxCount txtBox e  maxLength        if txtBox                  if txtBox value length  gt  maxLength                        txtBox value   txtBox value substring 0  maxLength                     if  checkSpecialKeys e                         return   txtBox value length  lt   maxLength                     function checkSpecialKeys e        if e keyCode   8  amp  amp  e keyCode  46  amp  amp  e keyCode  37  amp  amp  e keyCode  38  amp  amp  e keyCode  39  amp  amp  e keyCode  40          return false      else         return true       Ra  l Roa Answer did worked for me in case of copy paste  while this does

User · Answer

you can specify the max length for the multiline textbox in pageLoad Javascript Event  function pageLoad                             id   txtInput     attr  maxlength   10                            I have set the max length property of txtInput multiline textbox to 10 characters in pageLoad   Javascript function

User · Answer

I tried different approaches but every one had some weak points  i e  with cut and paste or browser compatibility   This is the solution I m using right now   function multilineTextBoxKeyUp textBox  e  maxLength        if   checkSpecialKeys e             var length   parseInt maxLength           if  textBox value length  gt  length                textBox value   textBox value substring 0  maxLength                      function multilineTextBoxKeyDown textBox  e  maxLength        var selectedText   document selection createRange   text      if   checkSpecialKeys e   amp  amp   e ctrlKey  amp  amp  selectedText length    0            var length   parseInt maxLength           if  textBox value length  gt  length - 1                if  e preventDefault                    e preventDefault                              else                   e returnValue   false                                   function checkSpecialKeys e        if  e keyCode    8  amp  amp  e keyCode    9  amp  amp  e keyCode    33  amp  amp  e keyCode    34  amp  amp  e keyCode    35  amp  amp  e keyCode    36  amp  amp  e keyCode    37  amp  amp  e keyCode    38  amp  amp  e keyCode    39  amp  amp  e keyCode    40            return false        else           return true            In this case  I m calling multilineTextBoxKeyUp on key up and multilineTextBoxKeyDown on key down   myTextBox Attributes Add  onkeyDown    multilineTextBoxKeyDown this  event       maxLength           myTextBox Attributes Add  onkeyUp    multilineTextBoxKeyUp this  event       maxLength

User · Answer

MaxLength is now supported as of  NET 4 7 2  so as long as you upgrade your project to  NET 4 7 2 or above  it will work automatically  You can see this in the release notes here - specifically   Enable ASP NET developers to specify MaxLength attribute for Multiline asp TextBox   449020  System Web dll  Bug

User · Answer

Things have changed in HTML5  ASPX   lt asp TextBox ID  quot txtBox quot  runat  quot server quot  maxlength  quot 2000 quot  TextMode  quot MultiLine quot  gt  lt  asp TextBox gt   C   if   IsPostBack        txtBox Attributes Add  quot maxlength quot   txtBox MaxLength ToString        Rendered HTML   lt textarea name  quot ctl00 DemoContentPlaceHolder txtBox quot  id  quot txtBox quot  maxlength  quot 2000 quot  gt  lt  textarea gt    The metadata for Attributes   Summary  Gets the collection of arbitrary attributes  for rendering only  that do not correspond to properties on the control  Returns  A System Web UI AttributeCollection of name and value pairs

User · Answer

use custom attribute maxsize  100    lt asp TextBox ID  txtAddress  runat  server   maxsize  100        Columns  17  Rows  4  TextMode  MultiLine  gt  lt  asp TextBox gt      lt script gt            textarea maxsize    each function                 this  attr  maxlength     this  attr  maxsize                this  removeAttr  maxsize                    lt  script gt    this will render like this    lt textarea name  ctl00 BodyContentPlac eHolder txtAddress  rows  4  cols  17  id  txtAddress  maxlength  100  gt  lt  textarea gt

User · Answer

Another way of fixing this for those browsers  Firefox  Chrome  Safari  that support maxlength on textareas  HTML5  without javascript is to derive a subclass of the System Web UI WebControls TextBox class and override the Render method  Then in the overridden method add the maxlength attribute before rendering as normal   protected override void Render HtmlTextWriter writer        if  this TextMode    TextBoxMode MultiLine            this MaxLength   0                writer AddAttribute HtmlTextWriterAttribute Maxlength  this MaxLength ToString                base Render writer

User · Answer

Have a look at this  The only way to solve it is by javascript as you tried    EDIT  Try changing the event to keypressup

User · Answer

try this javascript   function checkTextAreaMaxLength textBox e  length             var mLen   textBox  MaxLength            if null  mLen              mLen length           var maxLength   parseInt mLen           if  checkSpecialKeys e                      if textBox value length  gt  maxLength-1                         if window event   IE               e returnValue   false              else  Firefox                 e preventDefault                          function checkSpecialKeys e        if e keyCode   8  amp  amp  e keyCode  46  amp  amp  e keyCode  37  amp  amp  e keyCode  38  amp  amp  e keyCode  39  amp  amp  e keyCode  40          return false      else         return true      On the control invoke it like this    lt asp TextBox Rows  5  Columns  80  ID  txtCommentsForSearch  MaxLength  1999  onkeyDown  checkTextAreaMaxLength this event  1999      TextMode  multiLine  runat  server  gt   lt  asp TextBox gt    You could also just use the checkSpecialKeys function to validate the input on your javascript implementation

User · Answer

Use a regular expression validator instead  This will work on the client side using JavaScript  but also when JavaScript is disabled  as the length check will be performed on the server as well    The following example checks that the entered value is between 0 and 100 characters long    lt asp RegularExpressionValidator runat  server  ID  valInput      ControlToValidate  txtInput      ValidationExpression     s S  0 100        ErrorMessage  Please enter a maximum of 100 characters      Display  Dynamic  gt   lt  asp RegularExpressionValidator gt    There are of course more complex regexs you can use to better suit your purposes

User · Answer

The following example in JavaScript Jquery will do that-   lt telerik RadScriptBlock ID  RadScriptBlock1  runat  server  gt   lt script type  text javascript  gt       function count text  event              var keyCode   event keyCode              THIS IS FOR CONTROL KEY          var ctrlDown   event ctrlKey            var maxlength        lt   txtMEDaiSSOWebAddress1 ClientID  gt    val   length            if  maxlength  lt  200                 event returnValue   true                      else                 if   keyCode    8      keyCode    9      keyCode    46      keyCode    33      keyCode    27      keyCode    145      keyCode    19      keyCode    34      keyCode    37      keyCode    39      keyCode    16      keyCode    18                       keyCode    38      keyCode    40      keyCode    35      keyCode    36      ctrlDown  amp  amp  keyCode    88      ctrlDown  amp  amp  keyCode    65      ctrlDown  amp  amp  keyCode    67      ctrlDown  amp  amp  keyCode    86                                          event returnValue   true                                    else                     event returnValue   false                                          function substr text                    var txtWebAdd        lt   txtMEDaiSSOWebAddress1 ClientID  gt    val              var substrWebAdd            if  txtWebAdd length  gt  200                                              substrWebAdd   txtWebAdd substring 0  200                                                        lt   txtMEDaiSSOWebAddress1 ClientID  gt    val                         lt   txtMEDaiSSOWebAddress1 ClientID  gt    val substrWebAdd

User · Answer

keep it simple   Most modern browsers support a maxlength attribute on a text area  IE included   so simply add that attribute in code-behind   No JS  no Jquery  no inheritance  custom code  no fuss  no muss   VB Net   fld description attributes  maxlength     255   C   fld description Attributes  maxlength     255

User · Answer

Here s how we did it  keeps all code in one place     lt asp TextBox ID  TextBox1  runat  server  TextMode  MultiLine   gt   lt   TextBox1 Attributes  maxlength      1000     gt    Just in case someone still using webforms in 2018

User · Answer

Use HTML textarea with runat  server  to access it in server side   This solution has less pain than using javascript or regex    lt textarea runat  server  id  txt1  maxlength  100    gt    Note  To access Text Property in server side  you should use txt1 Value instead of txt1 Text

User · Answer

Roll your own   function Count text           asp net textarea maxlength doesnt work  do it by hand     var maxlength   2000    set your value here  or add a parm and pass it in      var object   document getElementById text id     get your object     if  object value length  gt  maxlength                 object focus      set focus to prevent jumping         object value   text value substring 0  maxlength     truncate the value         object scrollTop   object scrollHeight    scroll to the end to prevent jumping         return false            return true      Call like this    lt asp TextBox ID  foo  runat  server  Rows  3  TextMode  MultiLine  onKeyUp  javascript Count this    onChange  javascript Count this     gt  lt  asp TextBox gt

User · Answer

This is the same as  KeithK s answer  but with a few more details  First  create a new control based on TextBox   using System Web UI  using System Web UI WebControls   namespace MyProject       public class LimitedMultiLineTextBox   System Web UI WebControls TextBox               protected override void Render HtmlTextWriter writer                        this TextMode   TextBoxMode MultiLine               if  this MaxLength  gt  0                                writer AddAttribute HtmlTextWriterAttribute Maxlength  this MaxLength ToString                                base Render writer                         Note that the code above always sets the textmode to multiline     In order to use this  you need to register it on the aspx page  This is required because you ll need to reference it using the TagPrefix  otherwise compilation will complain about custom generic controls     lt    Register Assembly  MyProject  Namespace  MyProject  TagPrefix  mp    gt    lt mp LimitedMultiLineTextBox runat  server  Rows  3

User · Answer

txtInput   attr  maxLength   100

User · Answer

textarea maxlength    on  keydown paste   function  evt                if    this  val   length  gt    this  prop  maxlength                      if  evt type     paste                           this  val   this  val   substr 0    this  prop  maxlength                        else                       if   8  37  38  39  40  46  indexOf evt keyCode     -1                            evt returnValue   false                          evt preventDefault

[asp.net] Specifying maxlength for multiline textbox

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