// This example shows how to unsubscribe from changes of just some monitored
// items.
 
{
type
  TClientEventHandlers = class
    procedure OnDataChangeNotification(
      ASender: TObject;
      sender: OleVariant;
      const eventArgs: _EasyUADataChangeNotificationEventArgs);
  end;
 
procedure TClientEventHandlers.OnDataChangeNotification(
  ASender: TObject;
  sender: OleVariant;
  const eventArgs: _EasyUADataChangeNotificationEventArgs);
begin
  // Display the data
  // Remark: Production code would check eventArgs.Exception before accessing
  // eventArgs.AttributeData.
	WriteLn(eventArgs.Arguments.NodeDescriptor.ToString, ': ',
    eventArgs.AttributeData.ToString);
end;
}
 
class procedure UnsubscribeMultipleMonitoredItems.Some;
var
  Arguments: OleVariant;
  Client: TEasyUAClient;
  ClientEventHandlers: TClientEventHandlers;
  Handle: Cardinal;
  HandleArray: OleVariant;
  HandleSafeArray: PSafeArray;
  I: Cardinal;
  MonitoredItemArguments1, MonitoredItemArguments2, MonitoredItemArguments3:
    _EasyUAMonitoredItemArguments;
  MonitoringParameters: _UAMonitoringParameters;
  SelectedHandles: OleVariant;
begin
  // Instantiate the client object and hook events
  Client := TEasyUAClient.Create(nil);
  ClientEventHandlers := TClientEventHandlers.Create;
  Client.OnDataChangeNotification := ClientEventHandlers.OnDataChangeNotification;
 
  WriteLn;
  WriteLn('Subscribing...');
  MonitoringParameters := CoUAMonitoringParameters.Create;
  MonitoringParameters.SamplingInterval := 1000;
  MonitoredItemArguments1 := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments1.EndpointDescriptor.UrlString := 'http://opcua.demo-this.com:51211/UA/SampleServer';
  MonitoredItemArguments1.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/;i=10845';
  MonitoredItemArguments1.MonitoringParameters := MonitoringParameters;
  MonitoredItemArguments2 := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments2.EndpointDescriptor.UrlString := 'http://opcua.demo-this.com:51211/UA/SampleServer';
  MonitoredItemArguments2.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/;i=10853';
  MonitoredItemArguments2.MonitoringParameters := MonitoringParameters;
  MonitoredItemArguments3 := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments3.EndpointDescriptor.UrlString := 'http://opcua.demo-this.com:51211/UA/SampleServer';
  MonitoredItemArguments3.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/;i=10855';
  MonitoredItemArguments3.MonitoringParameters := MonitoringParameters;
  Arguments := VarArrayCreate([0, 2], varVariant);
  Arguments[0] := MonitoredItemArguments1;
  Arguments[1] := MonitoredItemArguments2;
  Arguments[2] := MonitoredItemArguments3;
 
  HandleSafeArray := Client.SubscribeMultipleMonitoredItems(PSafeArray(TVarData(Arguments).VArray));
  TVarData(HandleArray).VType := varArray or varVariant;
  TVarData(HandleArray).VArray := PVarArray(HandleSafeArray);
 
  for I := VarArrayLowBound(HandleArray, 1) to VarArrayHighBound(HandleArray, 1) do
  begin
      Handle := Cardinal(HandleArray[I]);
      WriteLn('HandleArray[', I, ']: ', Handle);
  end;
 
  WriteLn;
  WriteLn('Processing monitored item changed events for 10 seconds...');
  PumpSleep(10*1000);
 
  WriteLn;
  WriteLn('Unsubscribing from 2 monitored items...');
  SelectedHandles := VarArrayCreate([0, 1], varVariant);
  // We will unsubscribe from the first and third monitored item we have
  // previously subscribed to.
  SelectedHandles[0] := HandleArray[0];
  SelectedHandles[1] := HandleArray[2];
  Client.UnsubscribeMultipleMonitoredItems(PSafeArray(TVarData(SelectedHandles).VArray));
 
  WriteLn;
  WriteLn('Processing monitored item changed events for 10 seconds...');
  PumpSleep(10*1000);
 
  WriteLn;
  WriteLn('Unsubscribing from all remaining monitored items...');
  Client.UnsubscribeAllMonitoredItems;
 
  WriteLn;
  WriteLn('Waiting for 5 seconds...');
  Sleep(5*1000);
 
  WriteLn;
  WriteLn('Finished.');
  FreeAndNil(Client);
  FreeAndNil(ClientEventHandlers);
end;