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In Microsoft Windows applications programming, OLE Automation (later renamed to simply Automation [1] [2]) is an inter-process communication mechanism created by Microsoft.It is based on a subset of Component Object Model (COM) that was intended for use by scripting languages – originally Visual Basic – but now is used by several languages on Windows.
OLE 2.0 was the next evolution of OLE, sharing many of the same goals as version 1.0, but was re-implemented on top of the COM instead of using VTBLs directly. New features were OLE automation, drag-and-drop, in-place activation and structured storage.
COM is the basis for other Microsoft domain-specific component technologies including OLE, OLE Automation, ActiveX, COM+, and DCOM as well as implementations such as DirectX, Windows shell, UMDF, Windows Runtime, and Browser Helper Object. COM enables object use with only knowing its interface; not its internal implementation.
The OPC specification was based on the OLE, COM, and DCOM technologies developed by Microsoft Corporation for the Microsoft Windows operating system family. The specification defined a standard set of objects, interfaces e.g. IDL and methods for use in process control and manufacturing automation applications to facilitate interoperability.
The COM support in Microsoft Visual C++ allows developers to create a variety of COM objects, OLE Automation servers, and ActiveX controls. [1] [2] ATL includes an object wizard that sets up primary structure of the objects quickly with a minimum of hand coding. On the COM client side ATL provides smart pointers that deal with COM reference ...
IDispatch is the interface that exposes the OLE Automation protocol. [1] Extending IUnknown , it is one of the standard interfaces that can be exposed by COM objects. COM distinguishes between three interface types: custom that are VTABLE-based IUnknown interfaces, dispatch that are IDispatch interfaces supporting introspection, and dual ...
Interaction with the host application uses OLE Automation. Typically, the host application provides a type library and application programming interface (API) documentation which document how VBA programs can interact with the application. This documentation can be examined from inside the VBA development environment using its Object Browser.
The Collection class in OLE Automation can store items of different data types. Since the data type of these items cannot be known at compile time, the methods to add items to and retrieve items from a collection use variants. If in Visual Basic the For Each construct is used, the iterator variable must be of object type, or a variant.