Create TextArea control with working Maxlength property

We have found that text area (Multiline textbox) control in asp.net doesn't support the multiline property even you define that property.

so here is the solution for this problem

Code in .net Page

protected override void OnPreRender(EventArgs e)
{

if (MaxLength > 0 && TextMode == TextBoxMode.MultiLine)
{

// Add javascript handlers for paste and keypress
Attributes.Add("onkeypress", "doKeypress(this);");
Attributes.Add("onbeforepaste", "doBeforePaste(this);");
Attributes.Add("onpaste", "doPaste(this);");

// Add attribute for access of maxlength property on client-side
Attributes.Add("maxLength", this.MaxLength.ToString());

// Register client side include - only once per page

}
}

Code in JavaScript file

// Keep user from entering more than maxLength characters
function doKeypress(control)
{

maxLength = control.attributes["maxLength"].value;

value = control.value;

if(maxLength && value.length > maxLength-1)
{

event.returnValue = false;

maxLength = parseInt(maxLength);

}
}

// Cancel default behavior
function doBeforePaste(control)
{

maxLength = control.attributes["maxLength"].value;

if(maxLength)
{

event.returnValue = false;

}
}

// Cancel default behavior and create a new paste routine
function doPaste(control)
{

maxLength = control.attributes["maxLength"].value;

value = control.value;

if(maxLength)
{

event.returnValue = false;

maxLength = parseInt(maxLength);

var oTR = control.document.selection.createRange();

var iInsertLength = maxLength - value.length + oTR.text.length;

var sData = window.clipboardData.getData("Text").substr(0,iInsertLength);

oTR.text = sData;

}
}


using this code you can even check the copy paste and restrict the number of characters

now create a custom control and then use that control

set MaxLenght property of that control and you will be able to restrict the number of characters