Opc.Ua.Server.CustomNodeManager.SetMonitoringMode C# (CSharp) Method

        protected virtual ServiceResult SetMonitoringMode(
            ISystemContext context,
            IMonitoredItem monitoredItem,
            MonitoringMode monitoringMode, 
            out bool processed)
        {
            processed = false;

            // check for valid handle.
            MonitoredNode monitoredNode = monitoredItem.ManagerHandle as MonitoredNode;

            if (monitoredNode == null)
            {
                return ServiceResult.Good;
            }

            if (IsHandleInNamespace(monitoredNode.Node) == null)
            {
                return ServiceResult.Good;
            }

            // owned by this node manager.
            processed = true;

            // check for valid monitored item.
            DataChangeMonitoredItem datachangeItem = monitoredItem as DataChangeMonitoredItem;

            // update monitoring mode.
            MonitoringMode previousMode = datachangeItem.SetMonitoringMode(monitoringMode);

            // need to provide an immediate update after enabling.
            if (previousMode == MonitoringMode.Disabled && monitoringMode != MonitoringMode.Disabled)
            {
                DataValue initialValue = new DataValue();

                initialValue.Value = null;
                initialValue.ServerTimestamp = DateTime.UtcNow;
                initialValue.SourceTimestamp = DateTime.MinValue;
                initialValue.StatusCode = StatusCodes.Good;

                ServiceResult error = monitoredNode.Node.ReadAttribute(
                    context,
                    datachangeItem.AttributeId,
                    datachangeItem.IndexRange,
                    datachangeItem.DataEncoding,
                    initialValue);

                datachangeItem.QueueValue(initialValue, error);
            }
            
            // do any post processing.
            OnSetMonitoringMode(context, monitoredNode, datachangeItem, previousMode, monitoringMode);

            return ServiceResult.Good;
        }