Microsoft OLE Controls

• Control architecture for OLE components, part of Win32.
• The new version of OLE Controls is called ActiveX.
• Based on COM.
• OLE Controls are reusable embeddable automated user interface components implemented with OLE. They are implemented as auto-registering DLLs, that have three entry points: to register and unregister the OLE objects implemented by the DLL, and a QueryInterface request to the "class factory", that will manufacture a new object that supports the requested COM interface, if it can.
• See also OBJECT embedding in HTML, about embeding OLE controls in web pages.
• Type Library
  • Type libraries expose the interfaces of an OLE Control to other OLE-aware applications. Each OLE control must have a type library if one or more interfaces are to be exposed.
  • There's a COM interface called ITypeLibrary, that lets you browse all the type library information embeded in type libraries, DLLs, and other code containers. It describes all the symbols defined in a DLL, and their types and function signatures. It can describe C++ classes, C structures, function defintions, the types of their arguments, as well as COM interfaces, and OLE automation interfaces.
• CConnectionPoint class
  • Connection to another object for event and property change notification.
  • Connection points support multicasting, broadcasting to multiple sinks connected to the same interface.
• Every OLE Control must have a "class factory" that creates instances of it.
• The class factory is able to enforce a license.
• Extended Controls: OLE Containers have a "pad" that goes along with contained objects, that implements container specific properties and methods, and delegates to the associated control, seamlessly merging properties of control with control-specific container properties. This is based on COM aggregation.