AxcEasyUAClient := TAxcEasyUAClient.Create(self);
AxcEasyUAClient.OnEventNotification:=OnEvent;
res:=AxcEasyUAClient.OleServer.SubscribeEvent(servername,'ns=16;s=DiagnosisLogbook', 1000);
 
procedure TForm1.OnEvent(Sender: TObject; sender1: OleVariant; eventArgs: _EasyUAEventNotificationEventArgs);
var
  UAEventData:_UAEventData;
begin
  if assigned(eventArgs.Exception) then
    exit;
  //
  try
    memo1.Lines.Add(EventArgs.ToString);
    memo1.Lines.Add(EventArgs.DisplayString);
    memo1.Lines.Add(EventArgs.ErrorMessage);
    memo1.Lines.Add(inttostr(EventArgs.Diagnostics.Count));
    UAEventData :=EventArgs.EventData;
    if assigned(UAEventData) then // never happens, why
      memo1.Lines.Add(UAEventData.ToString);
  except
  end;
end;

type
  TClientEventHandlers2 = class
    procedure OnEventNotification(
      ASender: TObject;
      sender: OleVariant;
      const eventArgs: _EasyUAEventNotificationEventArgs);
  end;
 
procedure TClientEventHandlers2.OnEventNotification(
  ASender: TObject;
  sender: OleVariant;
  const eventArgs: _EasyUAEventNotificationEventArgs);
begin
  // Display the event
  WriteLn(eventArgs.ToString);
end;
 
class procedure SubscribeEvent.Main;
var
  Client: TEasyUAClient;
  ClientEventHandlers2: TClientEventHandlers2;
begin
  // Instantiate the client object and hook events
  Client := TEasyUAClient.Create(nil);
  ClientEventHandlers2 := TClientEventHandlers2.Create;
  Client.OnEventNotification := ClientEventHandlers2.OnEventNotification;
 
  WriteLn('Subscribing...');
  Client.SubscribeEvent(
    'opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer',
    'nsu=http://opcfoundation.org/UA/;i=2253',  // UAObjectIds.Server
    1000);
 
  WriteLn('Processing event notifications for 30 seconds...');
  PumpSleep(30*1000);
 
  //WriteLn('Unsubscribing...');
  Client.UnsubscribeAllMonitoredItems;
 
  WriteLn('Waiting for 5 seconds...');
  PumpSleep(5*1000);
end;

        class SelectClauses
        {
            public static void Main()
            {
                // Instantiate the client object and hook events
                var easyUAClient = new EasyUAClient();
                easyUAClient.EventNotification += easyUAClient_EventNotification;
 
                Console.WriteLine("Subscribing...");
                easyUAClient.SubscribeEvent(
                    "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer",
                    UAObjectIds.Server,
                    1000,
                    new UAAttributeFieldCollection
                    {
                        // Select specific fields using standard operand symbols
                        UABaseEventObject.Operands.NodeId,
                        UABaseEventObject.Operands.SourceNode,
                        UABaseEventObject.Operands.SourceName,
                        UABaseEventObject.Operands.Time,
 
                        // Select specific fields using an event type ID and a simple relative path
                        UAFilterElements.SimpleAttribute(UAObjectTypeIds.BaseEventType, "/Message"),
                        UAFilterElements.SimpleAttribute(UAObjectTypeIds.BaseEventType, "/Severity"),
                    });
 
                Console.WriteLine("Processing event notifications for 30 seconds...");
                System.Threading.Thread.Sleep(30 * 1000);
 
                Console.WriteLine("Unsubscribing...");
                easyUAClient.UnsubscribeAllMonitoredItems();
 
                Console.WriteLine("Waiting for 5 seconds...");
                System.Threading.Thread.Sleep(5 * 1000);
            }
 
            static void easyUAClient_EventNotification(object sender, EasyUAEventNotificationEventArgs e)
            {
                Console.WriteLine();
 
                // Display the event
                if (e.EventData == null)
                {
                    Console.WriteLine(e);
                    return;
                }
                Console.WriteLine("All fields:");
                foreach (KeyValuePair<UAAttributeField, ValueResult> pair in e.EventData.FieldResults)
                {
                    UAAttributeField attributeField = pair.Key;
                    ValueResult valueResult = pair.Value;
                    Console.WriteLine("  {0} -> {1}", attributeField, valueResult);
                }
                // Extracting a specific field using a standard operand symbol
                Console.WriteLine("Source name: {0}", 
                    e.EventData.FieldResults[UABaseEventObject.Operands.SourceName]);
                // Extracting a specific field using an event type ID and a simple relative path
                Console.WriteLine("Message: {0}", 
                    e.EventData.FieldResults[UAFilterElements.SimpleAttribute(UAObjectTypeIds.BaseEventType, "/Message")]);
            }
        }

        class WhereClause
        {
            public static void Main()
            {
                // Instantiate the client object and hook events
                var easyUAClient = new EasyUAClient();
                easyUAClient.EventNotification += easyUAClient_EventNotification;
 
                Console.WriteLine("Subscribing...");
                easyUAClient.SubscribeEvent(
                    "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer",
                    UAObjectIds.Server,
                    1000,
                    new UAEventFilterBuilder(
                        // Either the severity is >= 500, or the event comes from a specified source node
                        UAFilterElements.Or(
                            UAFilterElements.GreaterThanOrEqual(UABaseEventObject.Operands.Severity, 500),
                            UAFilterElements.Equals(
                                UABaseEventObject.Operands.SourceNode, 
                                new UANodeId("nsu=http://opcfoundation.org/Quickstarts/AlarmCondition;ns=2;s=1:Metals/SouthMotor"))),
                        UABaseEventObject.AllFields));
 
                Console.WriteLine("Processing event notifications for 30 seconds...");
                System.Threading.Thread.Sleep(30 * 1000);
 
                Console.WriteLine("Unsubscribing...");
                easyUAClient.UnsubscribeAllMonitoredItems();
 
                Console.WriteLine("Waiting for 5 seconds...");
                System.Threading.Thread.Sleep(5 * 1000);
            }
 
            static void easyUAClient_EventNotification(object sender, EasyUAEventNotificationEventArgs e)
            {
                // Display the event
                Console.WriteLine(e);
            }
        }