转自：http://bytes.com/topic/asp-net/answers/443065-textbox-value-change-select-other-item-dropdownlist
You need to add the below javascript in ur html section of the page
<script language="javascript">
function ShowValue()
{
document.Form1["textboxname"].value =
document.Form1["dropdownvalue"].value
}
</script>
and in the codebehind file add this line
Dropdowncontrol.Attributes.Add("onchange","javascr ipt:ShowValue()");
Now when you change the value in the drop down, the Textbox will be
filled without refreshing the page
http://forums.asp.net/t/1796597.aspx?How+to+select+a+value+in+dropdownlist
<head runat="server"> <script type="text/javascript"> function sethref() { var Textb = document.getElementById('<%=TextBox1.ClientID%>'); var parLab = document.getElementById('<%=Dropdown1.ClientID%>').options[document.getElementById('<%=Dropdown1.ClientID%>').selectedIndex].text; if(parLab!='--select deptname--'){ Textb.value = parLab } else{ Textb.value =''; } } </script> <title></title> </head> <body> <form id="form1" runat="server"> <div> <asp:Button ID="reload" runat="server" onclick="reload_Click"/> <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> <asp:DropDownList ID="Dropdown1" runat="server" onchange="sethref();"> <asp:ListItem>--select deptname--</asp:ListItem> <asp:ListItem>mama</asp:ListItem> <asp:ListItem>kaka</asp:ListItem> <asp:ListItem>nana</asp:ListItem> </asp:DropDownList> </div> </form> </body> </html>
http://blog.csdn.net/lvincent_china/article/details/7209517
<html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> <script type="text/javascript" src="../js/jquery-1.4.2.min.js"></script> <script type="text/javascript"> $(document).ready(function () { $('#<%=DropDownList1.ClientID %>').bind("keyup change", function () {//use bind() to attach a handler to the keyup and change events: $('#message').text(""); if ($(this).val() != "") {//Check if the selected value of the DropDownList is empty $('#message').text("Text:" + $(this).find(":selected").text() + "value:" + $(this).val()); //Retrieve the Text/Value pair and display in the div area 'message': } else { $('#message').text(""); } }) }) </script> </head> <body> <form id="form1" runat="server"> <div> <asp:DropDownList ID="DropDownList1" runat="server"> <asp:ListItem Value="" Text="please select"></asp:ListItem> <asp:ListItem Value="1" Text="Standard"></asp:ListItem> <asp:ListItem Value="2" Text="Silver"></asp:ListItem> <asp:ListItem Value="3" Text="Gold"></asp:ListItem> <asp:ListItem Value="4" Text="Premier"></asp:ListItem> </asp:DropDownList> </div> <div id="message"></div> </form> </body> </html>