The behavior of the Response.IsClientConnected is not consistent as it depends on the way the browser behaves when its stop button is clicked. If the browser notifies the server about the stop event Response.IsClientConnected
will return false and the code inside the if (!Response.IsClientConnected)
loop will be executed. For this reason, we do not recommend using this code for checking whether the RadProgressArea's cancel button has been clicked or not.
Currently RadUpload does not provide a way to find on the server whether the progress area's cancel button has been clicked. We have entered this issue in our feature requests list for further consideration and our plans are to provide such a functionality in one of the future updates of the control.
the Telerik team