For easy comprehension, there is just one communication object that you need to start with, for each OPC specification:

• For OPC Data Access, it is the EasyDAClient object.
• For OPC Alarms and Events, it is the EasyAEClient object.
• For OPC Unified Architecture (Client-Server), it is the EasyUAClient object.
• For OPC UA PubSub, it is the EasyUASubscriber object.

You achieve all OPC communication tasks by calling methods on one of these objects. The remainder of this paragraph describes the use of EasyDAClient object; the steps for EasyAEClient or EasyUAClient object are similar.

In order to be able to use one of these objects, you need to instantiate it first.

In OPC Data Client “Classic” and OPC Data Client-UA, there are two methods that you can use:

• Write the code that creates a new instance of the object, using an operator such as New (Visual Basic), new (Visual C#) or gcnew (Visual C++).
• Drag the component from the Toolbox to the designer surface. This works because they are derived from System.ComponentModel.Component (but is not limited to be used as a “full” component only). You can use this approach in Windows Forms applications, in Console applications and some other types of applications if you first add a designable component to your application. The designer creates code that instantiates the component, assigns a reference to it to a field in the parent component, and sets its properties as necessary. You can then use designer’s features such as the Properties grid to manipulate the component.

Note: In addition, there is a static Create() method on each EasyXXClient or EasyXXSubscriber class. This methods works the same as parameter-less constructor. For example (in C#), EasyUAClient.Create() is the same as new EasyUAClient().

For OPC Data Client-COM and OPC Data Client-UA for COM, the following table contains information needed to instantiate the objects.

Class Name	CLSID	ProgID
EasyAEClient	3643545B-221F-4960-BF47-8A4DDEC81A67	OpcLabs.EasyOpc.AlarmsAndEvents.EasyAEClient
EasyDAClient	6B0B5307-BCB6-4953-A832-BFCF952F7561	OpcLabs.EasyOpc.DataAccess.EasyDAClient
EasyUAClient	54AFB0EA-9809-4D1D-AFBE-0EC164C59A45	OpcLabs.EasyOpc.UA.EasyUAClient
EasyUASubscriber	EDC1F10E-3FC6-4604-9BC6-4FFF579D271A	OpcLabs.EasyOpc.UA.PubSub.EasyUASubscriber

As described in the “Naming Conventions”, in OPC Data Client-COM, all objects have ProgIDs that are identical to their qualified type names in .NET. For example, the ProgID of the main EasyUAClient is therefore “OpcLabs.EasyOpc.UA.EasyOpcUA”.

For COM development, CLSIDs of all objects and IIDs of all interfaces can also be found in the Reference documentation (look for the GuidAttribute on the classes and interfaces).