Here is how:
<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="TestTime._Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
<script language="javascript">
Function SetValue()
{
document.getElementById("txtTest").value = "Test";
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:TextBox ID="txtTest" runat="server" ReadOnly="true"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="PostBack" OnClientClick="SetValue();"/>
<asp:Label ID="lblTest" runat="server"></asp:Label>
</div>
</form>
</body>
</html>
Partial Public Class _Default
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
End Sub
Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
lblTest.Text = txtTest.Text 'txtTest.Text = ""
lblTest.Text = Request(txtTest.ClientID) 'Request(txtTest.ClientID)= "Test"
End Sub
End Class
Optionally, you can use the following line to set the readonly attribute:
txtMyTextBox.Attributes.Add("readonly", "readonly")
Reference:
ReadOnly Textbox ViewState in .NET 2.0
