ni.comni.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)

ni.comni.com

OutlineOutline

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.comni.com

What is ActiveX all about?What is ActiveX all about?

Demonstrations• Document objects• Automation• Controls• Containers

Demonstrations• Document objects• Automation• Controls• Containers

ni.comni.com

What is ActiveX?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.comni.com

Motivation for COM/ActiveXMotivation 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.comni.com

What About DLLs?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.comni.com

What is 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.comni.com

COM ServersCOM 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.comni.com

Object HierarchyObject Hierarchy

Top Level Objects

(Creatable)

Lower Level Objects

(Non-Creatable)

ni.comni.com

COM ObjectsCOM 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

ObjectInterface2

Interface1

Interface3

ni.comni.com

COM InterfacesCOM 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.comni.com

Interface BenefitsInterface 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.comni.com

Sample InterfacesSample Interfaces

IAnimal• Eat• Sleep• Walk

IDog : IAnimal• Bark• Fetch• ChaseCat

IAnimal• Eat• Sleep• Walk

IDog : IAnimal• Bark• Fetch• ChaseCat

IGuard• SoundAlarm• AttackBadGuy

IGuard• SoundAlarm• AttackBadGuy

ni.comni.com

Sample ObjectSample Object

Guard Dog ObjectIAnimal

IDog

IGuard

ni.comni.com

IUnknown InterfaceIUnknown 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.comni.com

IUnknown InterfaceIUnknown 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.comni.com

Registration of ServersRegistration 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.GuardDogCLSID

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.GuardDogCLSID

Default = “{E312522E-A7B7-11D1-A52E-0000F8751BA7}”

ni.comni.com

Event InterfacesEvent 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.comni.com

Example Event InterfaceExample Event Interface

IDogEvents• AmHungry• WantAttention• NeedToGoOutside

IDogEvents• AmHungry• WantAttention• NeedToGoOutside

ni.comni.com

IDispatch InterfaceIDispatch 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.comni.com

IDispatch InterfaceIDispatch 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.comni.com

COM/ActiveX ProgrammingCOM/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.comni.com

ActiveX and NI ProductsActiveX 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.comni.com

COM/ActiveX ResourcesCOM/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