OPC DA (Net API) How to identify response to Subscription.Refresh(object requestHandle, out IRequest request)|Classic OPC: DA, A&E, HDA, XML-DA, etc.|Forum|OPC Foundation

Can anyone explain or provide an example for how to identify the OnDataChange() event that matches a Refresh request? In my tests, each OnDataChange event comes with a null value for the requestHandle parameter.

I'm testing with code slightly modified from the available download "opc-net-api-sample-clients-2.01.107-20180130". I've changed the Refresh request code in SubscriptionsTreeCtrl to this:

private void Refresh(Subscription subscription)
{
    refreshRequestId++;
    try
    {
        IRequest requestToken = null;
        subscription.Refresh(refreshRequestId, out requestToken);
    }
    catch (Exception e)
    {
        MessageBox.Show(e.Message);
    }
}

... where "refreshRequestId" is an integer.

I can see that the "requestToken" gets values assigned. At this point I'm not concerned about its content so it's just a local variable.

In UpdatesListViewCtrl, the event handler:

    private void OnDataChange(object subscriptionHandle, object requestHandle, ItemValueResult[] values)

gets called with data changes but but 'requestHandle' is always null and there doesn't seem to be any other way to pair the callback with a specific refresh request.

Thanks