How to get 'the lost' monitored Item values (queued up) for a Subscription, when a broken connection between client and server is restored??|OPC UA Standard|Forum|OPC Foundation

Hi,

A question.

I am building a OPC UA Client. I am able to create a subscription containing some Monitoreditems.

On the OPC UA server these monitored items change value constantly.

I want to disconnect the client and wait for a while. Then I reconnect having my subscriptions back, but I also want all the monitored Item values queued up during the disconnect.

I am setting a queuesize:

monitoredItem.QueueSize = 100;

How to capture the content of the queue after a disconnect/connection error???

Should the ‘lost values’ be “new MonitoredItem_Notification” automatically when I reconnect?

Should the SubscriptionId be the same as before the connection was broken?

Should the sessionId be the same or will a new SessionId let med keep the existing subscriptions?

Many questions 🙂 

if (node.Displayname == “The node I want to monitor”)
{
MonitoredItem mon = CreateMonitoredItem((NodeId)node.reference.NodeId, node.Displayname);
m_subscription.AddItem(mon);
m_subscription.ApplyChanges();
subscribedClientNodes.Add(node);
}

————

private MonitoredItem CreateMonitoredItem(NodeId nodeId, string displayName)
{
if (m_subscription == null)
{

m_subscription = new Subscription(m_session.DefaultSubscription);

m_subscription.PublishingEnabled = true;
m_subscription.PublishingInterval = 3000;//1000;
m_subscription.KeepAliveCount = 10;
m_subscription.LifetimeCount = 10;
m_subscription.MaxNotificationsPerPublish = 1000;
m_subscription.Priority = 100;
bool cache = m_subscription.DisableMonitoredItemCache;

m_session.AddSubscription(m_subscription);

m_subscription.Create();
}

// add the new monitored item.
MonitoredItem monitoredItem = new MonitoredItem(m_subscription.DefaultItem);
//Each time a monitored item is sampled, the server evaluates the sample using a filter defined for each monitoreditem.
//The server uses the filter to determine if the sample should be reported. The type of filter is dependent on the type of item.
//DataChangeFilter for Variable, Eventfilter when monitoring Events. etc
//MonitoringFilter f = new MonitoringFilter();
//DataChangeFilter f = new DataChangeFilter();
//f.DeadbandValue

monitoredItem.StartNodeId = nodeId;
monitoredItem.AttributeId = Attributes.Value;
monitoredItem.DisplayName = displayName;
//Disabled, Sampling, (Report (includes sampling))
monitoredItem.MonitoringMode = MonitoringMode.Reporting;
//How often the Client wish to check for new values on the server. Must be 0 if item is an event.
//If a negative number the SamplingInterval is set equal to the PublishingInterval (inherited)
//The Subscriptions KeepAliveCount should always be longer than the SamplingInterval/PublishingInterval
monitoredItem.SamplingInterval = 500;
//Number of samples stored on the server between each reporting
monitoredItem.QueueSize = 100;
monitoredItem.DiscardOldest = true;//Discard oldest values when full
monitoredItem.CacheQueueSize = 100;

monitoredItem.Notification += m_MonitoredItem_Notification;

if (ServiceResult.IsBad(monitoredItem.Status.Error))
{
return null;
}

return monitoredItem;
}

——

private void MonitoredItem_Notification(MonitoredItem monitoredItem, MonitoredItemNotificationEventArgs e)
{
if (this.InvokeRequired)
{
this.BeginInvoke(new MonitoredItemNotificationEventHandler(MonitoredItem_Notification), monitoredItem, e);
return;
}

try
{
if (m_session == null)
{
return;
}

MonitoredItemNotification notification = e.NotificationValue as MonitoredItemNotification;

if (notification == null)
{
return;
}

foreach(MonitoredItem mon in monitoredItem.Subscription.MonitoredItems)
{
MonitoredItemNotification v = mon.LastValue as MonitoredItemNotification;
richTextBox1.AppendText(“
Iteration: ” + mon.DisplayName + ” value: ” + v.Value.Value + “sTime: “+v.Value.SourceTimestamp+” status: ” + mon.Status.QueueSize.ToString());
}
string sess = m_session.SessionId.Identifier.ToString();
string s = string.Format(“
MonitoredItem: {0}\t Value: {1}\t Status: {2}\t SourceTimeStamp: {3}”, monitoredItem.DisplayName, (notification.Value.WrappedValue.ToString().Length == 1) ? notification.Value.WrappedValue.ToString() + ” ” : notification.Value.WrappedValue.ToString(), notification.Value.StatusCode.ToString(), notification.Value.SourceTimestamp.ToLocalTime().ToString(“HH:mm:ss.fff”));
richTextBox1.AppendText(s + “
SessionId: ” + sess);
}
catch (Exception exception)
{
ClientUtils.HandleException(this.Text, exception);
}
}