How to limit the number of characters allowed in a textbox?

MaxLength does not apply to ASP.NET to Textboxes with TextMode="MultiLine". An easy way to do this and keep your MultiLine mark up would be to add:

onkeypress="return this.value.length<=10" 

with 10 being the limit. Like so:

<asp:TextBox ID="txtBodySMS" runat="server" Rows="10" onkeypress="return this.value.length<=10" TextMode="MultiLine" Width="100%"></asp:TextBox> 

EDIT Option One (Server side) The above example has some issues pointed out over the years. The underlying problem is a multi-line textBox is rendered as a text-area and MaxLength is removed. We can also fix in the C# or VB asp.net code behind of the page by forcing the re-attachment of MaxLength instead of attaching onkeypress.

 protected void Page_Load(object sender, EventArgs e) { txtBodySMS.Attributes.Add("maxlength", "10"); } 

EDIT Option Two (Client side): Here's a simple jquery solution. Include the following script in your head instead of attaching onkeypress or editing the server side code.

 $(document).ready(function () { $(".MultiLineLimit").on('change keydown paste input', function () { this.value = (this.value.length <= 10 ? this.value : this.value.substring(0, 10)); }); }); 

Now just add the MultiLineLimitclass to any of your <asp:TextBox> textbox of TextMode="MultiLine".

<asp:TextBox ID="txtBodySMS" CssClass="MultiLineLimit" runat="server" Rows="10" TextMode="MultiLine" Width="100%"></asp:TextBox> 

Remember in either scenario client side validation can be removed. If your storing this in a database it should always be validated server side as well.

Maximum character length Validation (Maximum 8 characters allowed)

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> <asp:RegularExpressionValidator Display = "Dynamic" ControlToValidate = "TextBox1" ID="RegularExpressionValidator1" ValidationExpression = "^[\s\S]{0,8}$" runat="server" ErrorMessage="Maximum 8 characters allowed."></asp:RegularExpressionValidator> 

Minimum character length Validation (Minimum 8 characters required)

<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox> <asp:RegularExpressionValidator Display = "Dynamic" ControlToValidate = "TextBox2" ID="RegularExpressionValidator2" ValidationExpression = "^[\s\S]{8,}$" runat="server" ErrorMessage="Minimum 8 characters required."></asp:RegularExpressionValidator> 

Minimum and Maximum character length Validation (Minimum 5 and Maximum 8 characters required)

<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox> <asp:RegularExpressionValidator Display = "Dynamic" ControlToValidate = "TextBox3" ID="RegularExpressionValidator3" ValidationExpression = "^[\s\S]{5,8}$" runat="server" ErrorMessage="Minimum 5 and Maximum 8 characters required."></asp:RegularExpressionValidator> 

MaxLength="Int32"

<asp:TextBox ID="txtBodySMS" runat="server" Rows="10" MaxLength="220" TextMode="MultiLine" Width="100%"></asp:TextBox> 

AFAIK maxlength has never worked in conjunction with the "multiline" mode. Therefore I would suggest some client-side js/jquery and server-side to get around the problem.

Just type below two line in .cs page load

textbox1.Attributes.Remove("MaxLength"); textbox1.Attributes.Add("MaxLength", "30"); 

Hope it will help !

<asp:TextBox ID="txtBodySMS" runat="server" Rows="10" MaxLength="220" TextMode="MultiLine" Width="100%"> </asp:TextBox> 

Set the MaxLength attribute to the number of characters.

You are looking for MaxLength: Look here

Have you tried setting the MaxLength Property on the TextBox? for Reference

Add an extender of type FliterTextBoxExtender for your text box
it should appear like that

<asp:TextBox ID="TxtCellular" runat="server"></asp:TextBox> <asp:FilteredTextBoxExtender ID="TxtCellular_FilteredTextBoxExtender" runat="server" Enabled="True" TargetControlID="TxtCellular" FilterType="Numbers"> </asp:FilteredTextBoxExtender> 

It is important to note that using MaxLength alone (with no other properties to add, just like the other answers) works ONLY for projects in .NET Framework 4.5 and above.

I'm using 4.5, and it worked for my project

<asp:TextBox ID="txtSample" MaxLength="3" runat="server"/> 

TextBox.MaxLength Property (MSDN Documentation)

It seems to be a curious oversight in the design of ASP.NET (leaving aside the anomaly with textareas) that you can set the MaxLength property of a textbox but there seems to be no way provided to enforce this limit server-side without explicitly adding a validator. That's a nuisance if you have lots of fields and just want to be sure that no-one is subventing the limits of the form by injecting their own POST data. So I wrote this, which seems to do the trick - obviously you might not want to force Response.End

Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load Dim colControls As Collection = New Collection getControlList(colControls, Me) For Each ctlNextPlease As Control In colControls If TypeOf (ctlNextPlease) Is TextBox Then Dim ctlTextBox As TextBox = ctlNextPlease If Len(Request(ctlTextBox.ID)) > ctlTextBox.MaxLength Then Response.Write("The value <i>" & Request(ctlTextBox.ID) & "</i> submitted for <b>" & ctlTextBox.ID & "</b> exceeds the permitted maximum length (" & ctlTextBox.MaxLength & ") for that value") Response.End() End If End If Next ... End Sub Public Shared Sub getControlList(ByRef colControls As Collection, ByVal rootControl As Control) colControls.Add(rootControl) If rootControl.Controls.Count > 0 Then For Each controlToSearch As Control In rootControl.Controls getControlList(colControls, controlToSearch) Next End If End Sub