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<noinclude>[[Category:Ide]]</noinclude>
'''How to Import an Existing COM Component'''
=== Terminology Used in COM ===

The Component Object Model (COM) is a way for software components to communicate with each other. It is a binary standard that allows any two components to communicate regardless of what machine they are running on (as long as the machines are connected), what operating systems the machines are running (as long as they support COM), and what language the components are written in. COM provides location transparency: it does not matter whether components are in DLLs or in EXEs. COM components are binary units of code that include packaging and registration code and that create COM objects. Each COM component, in the COM programming model, is a programming structure encapsulating both data and functionality. It is defined and allocated as a single unit and the only public access to the COM data and functionality is through the programming interfaces.

Each COM is simply a program module: a DLL or an EXE file. It can contain one or more COM ''components''. (In Microsoft MSDN terminology ''components'' are ''coclasses''.) Each component knows about several interfaces. (In MSDN terminology - each component can support several interfaces.) Each component supports the default interface '''iUnknown'''. Using the '''iUnknown::queryInterface/2->''' predicate from the '''iUnknown''' interface, one can retrieve references to all interfaces known to a component. Each interface can provide several predicates (methods).

The main aim of importing a COM component into your project is using predicates defined in this COM component. Therefore, the COM package generated for an imported COM component has to provide some wrapper (glue code) to methods implemented in the COM component. That is, the generated COM package must provide declarations of correspondent interfaces, predicates, and domains.

=== How to Create a New COM Package ===

To create a COM package providing the interface (wrapper) to some COM component, you should activate the '''File | New''' IDE command. Then in the left pane of the opened '''Create Project Item''' dialog you should select '''COM Package'''. Then the dialog accepts the following shape:

[[Image:Ide_How_COMPackage.png|center|frame|Creating '''New COM Package''' Dialog]]

After you fill in all required COM package settings, you can press the '''Create''' button. Then the IDE creates the package subdirectory, the package header file (<vp>XML.ph</vp> for the above picture), and the package implementation file (<vp>XML.pack</vp> for the above picture). They appear in the project tree in the Project Window after the created package is compiled.

=== Options ===

'''Name:'''
:In the '''Name''' edit control you should type in the name (<vp>XML</vp> on the picture) of the COM package (wrapping package) being created.

'''Parent Directory'''
:In the '''Parent Directory''' you should type in or select (using the '''Browse''' button) the ''parent directory'' for the package. The package will be placed into the subdirectory of this ''parent directory''. If you specify a non-existing name, then this directory will be created. By default, '''Parent Directory''' displays the directory selected in the project tree when you activate this dialog. If this directory is one of the project subdirectories, then its path is displayed relatively to the project root directory. If '''Parent Directory''' is empty, than it is equal to the project root directory.
:In the '''Parent Directory''' the IDE creates the new subdirectory with the name correspondent to the specified package name. (It is <vp>XML</vp> for the above picture.). The package will be placed into this subdirectory.

'''Source''' Group Box

Controls in this group box are used to specify a COM module ('''DLL''' or '''EXE''') from which a component should be imported. It contains the following controls:

*'''Type Library'''
*:When this option is checked ON, then in the edit control you should specify a file that contains the ''type library'' describing the COM component.
*:Press the '''Load''' button to activate the '''Load Type Library File''' dialog using which you can find and insert the name of the type library file into the edit control.
*:<br /><u>'''Attention!'''</u> Notice that you '''HAVE to''' press the '''Load''' button to enforce the IDE to load the COM information from the specified type library even if you directly type in the type library filename into the edit control.
*:<br />If a COM client (our program importing COM server components) needs using COM server predicates, then the client application must have information about predicates in COM server components. Predicates often return values and accept parameters. The COM client requires declarations of all these predicates (and domains) in order to use them. This information can be made known in several ways. The Microsoft recommended way is to create a type library. (Remember that type libraries do not provide Prolog declarations.) Type library information can be stored in files with the following filename extensions: '''.tlb''' (type library itself), '''.olb''' (multiple type libraries or foreign object libraries), '''.dll''' (COM DLLs can embed type library resources), '''.exe''' (COM EXEs can embed type library resources), '''.ocx''' (ActiveX controls).

*'''TypeLib ID'''
*:When this option is checked ON, then in the edit control you should specify the '''TypeLib ID''' of the ''type library'' for the COM component that you wish to import. The '''TypeLib ID''' is a universally unique identifier (UUID) under which the type library is registered in the Windows system registry. (See '''CLSID''' for more information.) The '''TypeLib ID''' should be specified as a string of hexadecimal numbers with the following format:
*: <vipbnf>{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}</vipbnf>
*:Then you '''MUST''' press the '''Load''' button to enforce the IDE to load COM information from the type library registered with this '''TypeLib ID'''.
*:In the system registry database you can find all registered '''TypeLib ID'''s under:
*:'''<vipbnf>HKEY_CLASSES_ROOT\TypeLib = {TypeLib ID}</vipbnf>'''

*'''CLSID'''
*:When this option is checked ON, then in the edit control you should specify the '''CLSID''' of the COM component that you wish to import. The '''CLSID''' should be specified as a string of hexadecimal numbers with the following format:
*:<vipbnf>{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}</vipbnf>
*:Then you '''MUST''' press the '''Load''' button to enforce the IDE to load COM information from the COM module that embeds the COM component with the specified '''CLSID'''.
*:<br />'''Note.''' Really a COM module can embed several COM components. If you wish to import one of these COM components, then you can specify a CLSID registered to any COM component in this COM module. (Later you will be able to specify the required COM component (or interface) in the list box in the  '''Import''' group box.)
*:<br />In MSDN terminology, '''CLSID''' is a class identifier. In the Visual Prolog PFC terminology (see the COM package description in the PFC) '''CLSID''' is a COM component identifier.
*:'''CLSID''' is a universally unique identifier (UUID) that identifies the type of a COM component. Each COM component has its '''CLSID''' in the Windows system registry database so that it can be loaded and used by other applications. For example, a spreadsheet can create worksheet components, chart components, and macrosheet components. Each of these components has its own '''CLSID''' that uniquely identifies this component to the system. That is, if your COM module (COM server or COM container) allows linking to its embedded components, then you need to register the special '''CLSID''' for each COM component embedded into the COM module.
*:The '''CLSID''' is stored in the Windows registry database under the following registry key:
*:'''<vipbnf>HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID = {CLSID}</vipbnf>'''
*:The '''CLSID''' is a 128-bit number (in the hexadecimal format) within a pair of curly braces. Typically, '''CLSID'''s (and other UUID values) are represented as strings of hexadecimal numbers with the following format:
*:<vipbnf>{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}</vipbnf>
*:For example,
*:<vipbnf>{4208fb66-e22a-11d1-a7d7-00a0c982c00d}</vipbnf>
*:You can use the '''UUIDGEN.exe''' tool to create a new UUID.
*:When you find a '''CLSID''' you can find the associated '''PROGID''' under the following registry sub-key:
*:'''<vipbnf>HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{CLSID}\ProgID = <programatic identifier></vipbnf>'''
*:See the '''PROGID''' options description below.
*:<br />'''Universally unique identifier (UUID)'''
*:<br />The universally unique identifier (UUID) is also known as the globally unique identifier (GUID). The UUID, or GUID, is a unique, 128-bit value used to identify objects. Objects can be OLE servers, interfaces, client objects, etc. Beginning from this moment objects will be identified with UUIDs.

*'''PROGID'''
*:When this option is checked ON. In the edit control you should specify the '''PROGID''' of the COM module from which you wish to import the COM component. The '''PROGID''' should be specified as a string of the following format:
*:'''<Program>.<Component>.<Version>'''
*:<br />Words are separated by dots as in <vp>Word.Document.6</vp>. (Blank spaces cannot be used.)
*:Then you '''MUST''' press the '''Load''' button to enforce the IDE to load COM information from the COM module registered with this '''PROGID'''.
*:'''PROGID'''s are versioned programmatic identifiers. '''PROGID'''s present human-readable versions of class identifiers ('''CLSID''') used to identify COM components. '''PROGID''' is a registry entry that can be associated with '''CLSID'''. Like '''CLSID''', '''PROGID''' identifies a COM component but with less precision because it is not guaranteed to be globally unique. The ''<vp>Version</vp>'' portion is optional but strongly recommended. Using ''<vp>Version</vp>'', even if there is only one version of the '''PROGID''', helps to avoid conflicts. It enables different versions of a component coexist without overwriting '''PROGID'''s. If you do not specify a version for a '''PROGID''', the default ''<vp>Version</vp>'' <vp>= 1</vp>.
*:How to find '''PROGID''' entries in the registry is described in the '''CLSID'''.

*'''IID'''
*:When this option is checked ON, then in the edit control you should specify the '''IID''' of the COM component interface that you wish to import.
*:'''IID''' is a universally unique identifier (UUID) that uniquely identifies a particular COM interface. '''IID''' should be specified as a string of hexadecimal numbers with the following format:
*:<vipbnf>{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}</vipbnf>
*:Then you '''MUST''' press the '''Load''' button to enforce the IDE to load COM information from the COM module that embeds the interface with the specified '''IID'''.
*:Really you can specify an '''IID''' registered to any interface embedded into the same COM module that embeds the interface you wish to import. (Later you will be able to specify the required COM component (or interface) in the list box in the '''Import''' group box.)
*:In the system registry database you can find all registered '''IID'''s under:
*:'''<vipbnf>HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface</vipbnf>'''
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