ni.com Understanding COM/ActiveX Jeff Paulter Staff Software Engineer Thurs Aug 17 10:15-11:30 a.m., 1:45-3:00 p.m. Ash (10A) Jeff Paulter Staff Software Engineer Thurs Aug 17 10:15-11:30 a.m., 1:45-3:00 p.m. Ash (10A)

ni.com Outline  What is ActiveX?  Why use COM/ActiveX  What is COM?  What are ActiveX/COM Servers Objects Interfaces More  What is ActiveX?  Why use COM/ActiveX  What is COM?  What are ActiveX/COM Servers Objects Interfaces More

ni.com What is ActiveX all about?  Demonstrations Document objects Automation Controls Containers  Demonstrations Document objects Automation Controls Containers

ni.com What is ActiveX?  The name for technologies built on top of COM  Examples include: Document objects ActiveX controls Automation OLE for process control (OPC)  Grew out of OLE  The name for technologies built on top of COM  Examples include: Document objects ActiveX controls Automation OLE for process control (OPC)  Grew out of OLE

ni.com Motivation for COM/ActiveX  Component software development Reuse of binary software components Create and use components from various languages Update components without recompiling or breaking existing clients  Object-based model  Distributed software  Location transparency  Component software development Reuse of binary software components Create and use components from various languages Update components without recompiling or breaking existing clients  Object-based model  Distributed software  Location transparency

ni.com What About DLLs?  Calling conventions can vary  DLLs are not object based (Flat API)  Versioning can be difficult  Memory management concerns  Linkage issues  Calling conventions can vary  DLLs are not object based (Flat API)  Versioning can be difficult  Memory management concerns  Linkage issues

ni.com What is COM?  Component object model  Binary and network standard  Run-time system Calls across network Location transparency Security  Component object model  Binary and network standard  Run-time system Calls across network Location transparency Security

ni.com COM Servers  Can be DLLs or EXEs  Provide objects for clients A single server can provide implementations for more than one object The set of objects that a server provides and the relationships between them is referred to as an object hierarchy  Are activated by the COM run-time services  Can be DLLs or EXEs  Provide objects for clients A single server can provide implementations for more than one object The set of objects that a server provides and the relationships between them is referred to as an object hierarchy  Are activated by the COM run-time services

ni.com Object Hierarchy Top Level Objects (Creatable) Lower Level Objects (Non-Creatable)

ni.com COM Objects  Clients view objects as black boxes  Clients communicate with objects only through interfaces  Objects can handle more than one interface  Clients view objects as black boxes  Clients communicate with objects only through interfaces  Objects can handle more than one interface Object Interface2 Interface1 Interface3

ni.com COM Interfaces  Sets of related methods  Immutable contracts  Implementations not described NO member data (functions only)  COM defines a standard for in-memory layout of interfaces  Sets of related methods  Immutable contracts  Implementations not described NO member data (functions only)  COM defines a standard for in-memory layout of interfaces

ni.com Interface Benefits  Compiler neutral  Language neutral  Object implementations can change without affecting clients Clients never need to be recompiled  Versioning  Compiler neutral  Language neutral  Object implementations can change without affecting clients Clients never need to be recompiled  Versioning

ni.com Sample Interfaces  IAnimal Eat Sleep Walk  IDog : IAnimal Bark Fetch ChaseCat  IAnimal Eat Sleep Walk  IDog : IAnimal Bark Fetch ChaseCat  IGuard SoundAlarm AttackBadGuy

ni.com Sample Object Guard Dog Object IAnimal IDog IGuard

ni.com IUnknown Interface  Every COM interface inherits from IUnknown  IUnknown includes functionality needed by every object Provides a mechanism for clients to obtain one interface from another interface Provides object lifetime manangement  Every COM interface inherits from IUnknown  IUnknown includes functionality needed by every object Provides a mechanism for clients to obtain one interface from another interface Provides object lifetime manangement

ni.com IUnknown Interface  Mechanism to get from one interface on an object to another interface on the object HRESULT QueryInterface (REFIID riid, void **ppvObject);  Mechanism to manage object lifetimes Clients do not delete COM objects directly COM objects are responsible for deleting themselves COM objects are reference counted ULONG AddRef ( ); ULONG Release ( );  Mechanism to get from one interface on an object to another interface on the object HRESULT QueryInterface (REFIID riid, void **ppvObject);  Mechanism to manage object lifetimes Clients do not delete COM objects directly COM objects are responsible for deleting themselves COM objects are reference counted ULONG AddRef ( ); ULONG Release ( );

ni.com Registration of Servers  Servers are registered with the system HKEY_CLASSES_ROOT CLSID {E312522E-A7B7-11D1-A52E-0000F8751BA7} Default = “Guard Dog Object” InprocServer32 = "D:\Examples\AnimalLib\AnimalLib.dll" AnimalLib.GuardDog CLSID Default = “{E312522E-A7B7-11D1-A52E- 0000F8751BA7}”  Servers are registered with the system HKEY_CLASSES_ROOT CLSID {E312522E-A7B7-11D1-A52E-0000F8751BA7} Default = “Guard Dog Object” InprocServer32 = "D:\Examples\AnimalLib\AnimalLib.dll" AnimalLib.GuardDog CLSID Default = “{E312522E-A7B7-11D1-A52E- 0000F8751BA7}”

ni.com Event Interfaces  Interface provides communication from the server back to the client  Server defines an interface that it calls to notify the client that an event occurred  Client supplies server with a pointer to the interface  Client’s code is executed when the server calls methods in the event interface  Interface provides communication from the server back to the client  Server defines an interface that it calls to notify the client that an event occurred  Client supplies server with a pointer to the interface  Client’s code is executed when the server calls methods in the event interface

ni.com Example Event Interface  IDogEvents AmHungry WantAttention NeedToGoOutside  IDogEvents AmHungry WantAttention NeedToGoOutside

ni.com IDispatch Interface  Automation servers must handle IDispatch  ActiveX controls must handle IDispatch  IDispatch gives scripting clients access to COM objects Microsoft Office Internet Explorer Old versions of Visual Basic  Automation servers must handle IDispatch  ActiveX controls must handle IDispatch  IDispatch gives scripting clients access to COM objects Microsoft Office Internet Explorer Old versions of Visual Basic

ni.com IDispatch Interface  IDispatch::Invoke provides access to an entire interface through a single function  Clients use the Invoke function to call all methods Specify method by method ID Pass parameters in a single large structure  Invoke understands only Automation types Yes: int, double, enum, boolean, structures Yes: BSTR, SafeArray, Variant No: unions, C style arrays, C style strings  IDispatch::Invoke provides access to an entire interface through a single function  Clients use the Invoke function to call all methods Specify method by method ID Pass parameters in a single large structure  Invoke understands only Automation types Yes: int, double, enum, boolean, structures Yes: BSTR, SafeArray, Variant No: unions, C style arrays, C style strings

ni.com COM/ActiveX Programming  Many environments provide some tools to make writing COM servers and clients easier Wrappers for accessing COM servers Wizards to create skeleton servers or controls Tools to add interfaces, methods, properties Free implementations of some standard interfaces  Measurement Studio Visual Basic, Visual C++, LabWindows/CVI  LabVIEW™  Many environments provide some tools to make writing COM servers and clients easier Wrappers for accessing COM servers Wizards to create skeleton servers or controls Tools to add interfaces, methods, properties Free implementations of some standard interfaces  Measurement Studio Visual Basic, Visual C++, LabWindows/CVI  LabVIEW™

ni.com ActiveX and NI Products  ActiveX controls Measurement Studio  Containers LabVIEW, BridgeVIEW™  Automation servers LabVIEW, Measurement Studio, HiQ™, DataSocket™  Clients LabVIEW, BridgeVIEW, Measurement Studio, TestStand™  ActiveX controls Measurement Studio  Containers LabVIEW, BridgeVIEW™  Automation servers LabVIEW, Measurement Studio, HiQ™, DataSocket™  Clients LabVIEW, BridgeVIEW, Measurement Studio, TestStand™

ni.com COM/ActiveX Resources  Essential COM Don Box (Addison-Wesley, 1998)  Inside COM Dale Rogerson (Microsoft Press, 1997)  Various MSDN Articles  NI Product Examples  Essential COM Don Box (Addison-Wesley, 1998)  Inside COM Dale Rogerson (Microsoft Press, 1997)  Various MSDN Articles  NI Product Examples