How to develop OPC clients in Delphi

OPC Delphi Code Samples

QuickOPC is unbelievably easy to use - here is an Object Pascal example which reads and displays OPC data from a common OPC Data Access server:

 

var
  EasyDAClient: IEasyDAClient;
begin
  { Create EasyOPC-DA component }
  EasyDAClient := CoEasyDAClient.Create;

  { Read item value and display it }
  Edit1.Text := EasyDAClient.ReadItemValue('', 'OPCLabs.KitServer.2',
    'Demo.Single', EmptyParam, EmptyParam);
end;

Do you think it can be any simpler? But the simplicity is not the only advantage; the component is also very powerful. Using complex heuristic algorithms to optimize itself on the fly, it provides the most efficient, fastest access to the OPC data.

It is also easy to communicate with an OPC Unified Architecture (OPC-UA) server:

var
  Client: TEasyUAClient;
  Value: OleVariant;
begin
  // Instantiate the client object
  Client := TEasyUAClient.Create(nil);

  Value := Client.ReadValue(
    'opc.tcp://opcua.demo-this.com:51210/UA/SampleServer',
    'nsu=http://test.org/UA/Data/;i=10853');
  WriteLn('value: ', Value);
end;

Application-side subscriptions are possible, too. The Delphi example below shows how subscribe to changes of a single item and display the value of the item with each change.

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 SubscribeDataChange.Main;
var
  Client: TEasyUAClient;
  ClientEventHandlers: TClientEventHandlers;
begin
  // Instantiate the client object and hook events
  Client := TEasyUAClient.Create(nil);
  ClientEventHandlers := TClientEventHandlers.Create;
  Client.OnDataChangeNotification := ClientEventHandlers.OnDataChangeNotification;

  WriteLn('Subscribing...');
  Client.SubscribeDataChange(
    'opc.tcp://opcua.demo-this.com:51210/UA/SampleServer',
    'nsu=http://test.org/UA/Data/;i=10853',
    1000);

  WriteLn('Processing data change events for 1 minute...');
  PumpSleep(60*1000);
end;