Hi @Babloo18v,
try below code.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default3.aspx.cs" Inherits="Default3" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList ID="ddltype" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddltype_SelectedIndexChanged">
<asp:ListItem Text="Select type" Value=""></asp:ListItem>
<asp:ListItem Text="Default" Value="0"></asp:ListItem>
<asp:ListItem Text="Conditionall" Value="1"></asp:ListItem>
</asp:DropDownList>
<asp:TextBox ID="txttype" runat="server" Text="Default" Enabled="false"></asp:TextBox>
</div>
</form>
</body>
</html>
using System;
public partial class Default3 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void ddltype_SelectedIndexChanged(object sender, EventArgs e)
{
if (ddltype.SelectedValue == "")
{
Response.Write("<script>alert('Please Select Type!');</script>");
}
else if (ddltype.SelectedValue == "0")
{
txttype.Enabled = false;
txttype.Text = "Default";
}
else if (ddltype.SelectedValue == "1")
{
txttype.Enabled = true;
txttype.Text = "";
txttype.Focus();
}
}
}