UpDown Web Form Code-Behind Class File
using System;
namespace ControlsBook2Web.Ch08
{
public partial class UpDown : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
timelabel.Text = DateTime.Now.ToString();
changelabel.Text = "";
}
protected void updown1_ValueChanged(object sender, System.EventArgs e)
{
changelabel.Text = " UpDown value is now " + updown1.Value + "!";
}
}
}
Client Callbacks
The normal client server interaction in ASP.NET is driven by the postback process, which shuttles
HTML form and ViewState data for processing to the server and causes the subsequent refresh
of the results in the browser once they are sent back. While making life simpler from a web development
perspective and the foundation of the ASP.NET control model, it impacts the end-user
experience in negative ways. At a minimum, the flashing of the HTML can be annoying for the
user, and the entire experience may be perceived as unresponsive if there is significant latency
observed when communicating across the network for even the smallest UI change.
Client callbacks are a feature added to the ASP.NET 2.0 release that provide a standardized
way to make requests for pieces of data or content from client-side scripts without the need to
build the underlying plumbing to make such a call or change the ASP.
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