问题
I have read and saw example for COM, but I couldn't clearly get there Interface difference.
回答1:
IUnknown is the primal COM interface. It provides the basic ability to "cast" a instance of a COM object to any of it's supported interfaces (QueryInterface).
IDispatch builds on IUnknown adding the facility to discover at run-time the attributes and interfaces supported by the specified COM object. This allows for late-binding and dynamic-binding. A remedial reflection of sorts. With IDispatch, an application can discover the capability of components and invoke discovered methods (which was simplistically called automation).
See Implementing the IDispatch Interface [Automation] on MSDN (resurrected from WayBack Machine - current online version).
回答2:
IUnkown is the basic interface for all COM interfaces.
IDispatch exposes an interfacea for objects, methods and properties to programming tools and other applications that support Automation.
回答3:
The IDispatch interface inherits from the IUnknown interface. Please have a look at the below link.
IDispatch
IUnknown
来源：https://stackoverflow.com/questions/37937360/what-is-the-difference-between-idispatch-and-iunkown-in-com