RadComboBox for ASP.NET

Setting default text to the combobox Send comments on this topic.
TroubleShooting > Setting default text to the combobox

Glossary Item Box

Telerik RadComboBox version 2.5.3+

You can simply set the Text property of the RadComboBox class either in the aspx combobox definition or in the codebehind, like:

ASPX Copy Code
<rad:RadComboBox
   
id="RadComboBox1"
   
runat="server"
   
AllowCustomText="True"
   
Text="Select an Item"/>

CodeBehind:

C# Copy Code
RadComboBox1.Text = "Select an Item";

Also, you should keep into account that the AllowCustomText property should be enabled. 

Telerik RadComboBox version 2.5.2

To set default text to the input field of the combobox, you can use the following approach.

Example:

ASPX Copy Code
<body onload="SetText()">
   
<form id="form1" runat="server">
       
<script language="javascript" type="text/javascript">
           
function SetText()
           {
               var combo =
<%=RadComboBox1.ClientID %>;
               combo.SetText("DefaultText");
           }
       
</script>
       
<rad:RadComboBox ID="RadComboBox1" runat="server">
       
</rad:RadComboBox>
   
</form>
</
body>

The result of the above code will be: