// This example shows how to select fields for event notifications.
 
type
  TClientEventHandlers4 = class
    procedure OnEventNotification(
      Sender: TObject;
      sender0: OleVariant;
      eventArgs: _EasyUAEventNotificationEventArgs);
  end;
 
procedure TClientEventHandlers4.OnEventNotification(
  Sender: TObject;
  sender0: OleVariant;
  eventArgs: _EasyUAEventNotificationEventArgs);
 
  function ToUAAttributeField(Operand: UASimpleAttributeOperand): UAAttributeField;
  var
    AttributeField: UAAttributeField;
  begin
    AttributeField := CoUAAttributeField.Create;
    AttributeField.Operand := Operand;
    ToUAAttributeField := AttributeField;
  end;
 
  function UAFilterElements_SimpleAttribute(TypeId: UANodeId; SimpleRelativeBrowsePathString: string): UASimpleAttributeOperand;
  var
    Operand: UASimpleAttributeOperand;
    BrowsePathParser: UABrowsePathParser;
  begin
    BrowsePathParser := CoUABrowsePathParser.Create;
    Operand := CoUASimpleAttributeOperand.Create;
    Operand.TypeId.NodeId := TypeId;
    Operand.QualifiedNames := BrowsePathParser.ParseRelative(SimpleRelativeBrowsePathString).ToUAQualifiedNameCollection;
    UAFilterElements_SimpleAttribute := Operand;
  end;
 
  function ObjectTypeIds_BaseEventType: UANodeId;
  var
    NodeId: UANodeId;
  begin
    NodeId := CoUANodeId.Create;
    NodeId.StandardName := 'BaseEventType';
    ObjectTypeIds_BaseEventType := NodeId;
  end;
 
var
  Count: Cardinal;
  Element: OleVariant;
  EntryEnumerator: IEnumVariant;
  Entry: DictionaryEntry2;
  AttributeField: UAAttributeField;
  AValueResult: ValueResult;
begin
  WriteLn;
 
  // Display the event
  if eventArgs.EventData = nil then
  begin
    WriteLn(eventArgs.ToString);
    Exit;
  end;
  WriteLn('All fields:');
  EntryEnumerator := eventArgs.EventData.FieldResults.GetEnumerator;
  while EntryEnumerator.Next(1, Element, Count) = S_OK do
  begin
    Entry := IUnknown(Element) as DictionaryEntry2;
    AttributeField := IUnknown(Entry.key) as UAAttributeField;
    AValueResult := IUnknown(Entry.Value) as ValueResult;
    WriteLn('  ', AttributeField.ToString, ' -> ', AValueResult.ToString);
  end;
  // Extracting a specific field using an event type ID and a simple relative path
  WriteLn('Source name: ',
    eventArgs.EventData.FieldResults[ToUAAttributeField(UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/SourceName'))].ToString);
  WriteLn('Message: ',
    eventArgs.EventData.FieldResults[ToUAAttributeField(UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Message'))].ToString);
end;
 
class procedure SelectClauses.Main;
 
  function ToUAAttributeField(Operand: UASimpleAttributeOperand): UAAttributeField;
  var
    AttributeField: UAAttributeField;
  begin
    AttributeField := CoUAAttributeField.Create;
    AttributeField.Operand := Operand;
    ToUAAttributeField := AttributeField;
  end;
 
  function ObjectTypeIds_BaseEventType: UANodeId;
  var
    NodeId: UANodeId;
  begin
    NodeId := CoUANodeId.Create;
    NodeId.StandardName := 'BaseEventType';
    ObjectTypeIds_BaseEventType := NodeId;
  end;
 
  function UABaseEventObject_Operands_NodeId: UASimpleAttributeOperand;
  var
    Operand: UASimpleAttributeOperand;
  begin
    Operand := CoUASimpleAttributeOperand.Create;
    Operand.TypeId.NodeId.StandardName := 'BaseEventType';
    Operand.AttributeId := UAAttributeId_NodeId;
    UABaseEventObject_Operands_NodeId := Operand;
  end;
 
  function UAFilterElements_SimpleAttribute(TypeId: UANodeId; SimpleRelativeBrowsePathString: string): UASimpleAttributeOperand;
  var
    Operand: UASimpleAttributeOperand;
    BrowsePathParser: UABrowsePathParser;
  begin
    BrowsePathParser := CoUABrowsePathParser.Create;
    Operand := CoUASimpleAttributeOperand.Create;
    Operand.TypeId.NodeId := TypeId;
    Operand.QualifiedNames := BrowsePathParser.ParseRelative(SimpleRelativeBrowsePathString).ToUAQualifiedNameCollection;
    UAFilterElements_SimpleAttribute := Operand;
  end;
 
var
  Arguments: OleVariant;
  EvsClient: TEvsEasyUAClient;
  Client: EasyUAClient;
  ClientEventHandlers: TClientEventHandlers4;
  Handle: Cardinal;
  HandleArray: OleVariant;
  MonitoredItemArguments: EasyUAMonitoredItemArguments;
  MonitoringParameters: UAMonitoringParameters;
  EventFilter: UAEventFilter;
  SelectClauses: UAAttributeFieldCollection;
begin
  // Instantiate the client object and hook events
  EvsClient := TEvsEasyUAClient.Create(nil);
  Client := EvsClient.ComServer;
  ClientEventHandlers := TClientEventHandlers4.Create;
  EvsClient.OnEventNotification := @ClientEventHandlers.OnEventNotification;
 
  WriteLn('Subscribing...');
 
  SelectClauses := CoUAAttributeFieldCollection.Create;
  // Select specific fields using an event type ID and a simple relative path
  SelectClauses.Add(ToUAAttributeField(UABaseEventObject_Operands_NodeId));
  SelectClauses.Add(ToUAAttributeField(UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/SourceNode')));
  SelectClauses.Add(ToUAAttributeField(UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/SourceName')));
  SelectClauses.Add(ToUAAttributeField(UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Time')));
  SelectClauses.Add(ToUAAttributeField(UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Message')));
  SelectClauses.Add(ToUAAttributeField(UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Severity')));
 
  EventFilter := CoUAEventFilter.Create;
  EventFilter.SelectClauses := SelectClauses;
 
  MonitoringParameters := CoUAMonitoringParameters.Create;
  MonitoringParameters.SamplingInterval := 1000;
  MonitoringParameters.EventFilter := EventFilter;
  MonitoringParameters.QueueSize := 1000;
 
  MonitoredItemArguments := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments.EndpointDescriptor.UrlString := 'opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer';
  MonitoredItemArguments.NodeDescriptor.NodeId.StandardName := 'Server';
  MonitoredItemArguments.MonitoringParameters := MonitoringParameters;
  //MonitoredItemArguments.SubscriptionParameters.PublishingInterval := 0;
  MonitoredItemArguments.AttributeId := UAAttributeId_EventNotifier;
 
  Arguments := VarArrayCreate([0, 0], varVariant);
  Arguments[0] := MonitoredItemArguments;
 
  TVarData(HandleArray).VType := varArray or varVariant;
  TVarData(HandleArray).VArray := PVarArray(
    Client.SubscribeMultipleMonitoredItems(PSafeArray(TVarData(Arguments).VArray)));
 
  WriteLn('Processing event notifications for 30 seconds...');
  PumpSleep(30*1000);
 
  WriteLn('Unsubscribing...');
  Client.UnsubscribeAllMonitoredItems;
 
  WriteLn('Waiting for 5 seconds...');
  PumpSleep(5*1000);
 
  WriteLn('Done...');
end;