New to Telerik UI for ASP.NET AJAX? Download free 30-day trial

Combobox Slow Callback

Imagine the following approach:

  • Combobox items are added in the Page_Load event. The items are added from a huge datasource. The code is placed in if (!Page.IsPostBack) block RadComboBox is in a callback mode - the items are also added in the ItemsRequested event of the combobox.

  • The code in the if (!Page.IsPostBack) block is executed upon each postback. This is what makes the combobox performance slow.

Telerik RadComboBox performs a "light" callback to the server - no ViewState information is sent to the server and the Page.IsPostBack property is set to False when the combobox is in a callback mode.

In addition, the Page_Load method is called before the ItemsRequested event. Therefore, all page initialization code is fired, too.To avoid re-executing of the code in the Page_Load event, you should check for both Page.IsPostBack and Page.IsCallBack:

protected void Page_Load(object sender, EventArgs e)
    if (!Page.IsPostBack && !Page.IsCallBack)
        //Initialization code 
In this article