ICallbackEventHandler GetCallbackTarget ()
{
string callbackTarget = _requestValueCollection [CallbackSourceID];
if (callbackTarget == null || callbackTarget.Length == 0)
throw new HttpException ("Callback target not provided.");
Control targetControl = FindControl (callbackTarget, true);
ICallbackEventHandler target = targetControl as ICallbackEventHandler;
if (target == null)
throw new HttpException (string.Format ("Invalid callback target '{0}'.", callbackTarget));
return target;
}