source: trunk/doc/src/qaxserver.qdoc@ 109

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/*!
    \module QAxServer
    \title QAxServer Module
    \contentspage Qt's Modules
    \previouspage QAxContainer
    \nextpage QtDBus module
    \ingroup modules

    \brief The QAxServer module is a Windows-only static library that
    you can use to turn a standard Qt binary into a COM server. 

    The QAxServer module is part of the \l ActiveQt framework. It
    consists of three classes:

    \list
    \o QAxFactory defines a factory for the creation of COM objects.
    \o QAxBindable provides an interface between the Qt widget and the 
       COM object.
    \o QAxAggregated can be subclassed to implement additional COM interfaces.
    \endlist

    Some \l{Qt Examples#ActiveQt}{example implementations} of ActiveX
    controls and COM objects are provided.

    \sa {ActiveQt Framework}

    Topics:

    \tableofcontents

    \section1 Using the Library

    To turn a standard Qt application into a COM server using the
    QAxServer library you must add \c qaxserver as a CONFIG setting
    in your \c .pro file.

    An out-of-process executable server is generated from a \c .pro
    file like this:

    \snippet doc/src/snippets/code/doc_src_qaxserver.qdoc 0

    To build an in-process server, use a \c .pro file like this:
    \snippet doc/src/snippets/code/doc_src_qaxserver.qdoc 1

    The files \c qaxserver.rc and \c qaxserver.def are part of the
    framework and can be used from their usual location (specify a
    path in the \c .pro file), or copied into the project directory.
    You can modify these files as long as it includes any file as the
    type library entry, ie. you can add version information or specify
    a different toolbox icon.

    The \c qaxserver configuration will cause the \c qmake tool to add the 
    required build steps to the build system:

    \list
    \o Link the binary against \c qaxserver.lib instead of \c qtmain.lib
    \o Call the \l idc tool to generate an IDL file for the COM server
    \o Compile the IDL into a type library using the MIDL tool (part of the
    compiler installation)
    \o Attach the resulting type library as a binary resource to the server
    binary (again using the \l idc tool)
    \o Register the server
    \endlist

    Note that the QAxServer build system is not supported on Windows 98/ME
    (attaching of resources to a binary is not possible there), but a server 
    built on Windows NT/2000/XP will work on previous Windows versions as well.

    To skip the post-processing step, also set the \c qaxserver_no_postlink
    configuration.

    Additionally you can specify a version number using the \c VERSION
    variable, e.g.

    \snippet doc/src/snippets/code/doc_src_qaxserver.qdoc 2

    The version number specified will be used as the version of the type
    library and of the server when registering.

    \section2 Out-of-Process vs. In-Process

    Whether your COM server should run as a stand-alone executable
    or as a shared library in the client process depends mainly on the
    type of COM objects you want to provide in the server. 

    An executable server has the advantage of being able to run as a
    stand-alone application, but adds considerable overhead to the
    communication between the COM client and the COM object. If the
    control has a programming error only the server process running
    the control will crash, and the client application will probably
    continue to run. Not all COM clients support executable servers.

    An in-process server is usually smaller and has faster startup
    time. The communication between client and server is done directly
    through virtual function calls and does not introduce the overhead
    required for remote procedure calls. However, if the server crashes the
    client application is likely to crash as well, and not every 
    functionality is available for in-process servers (i.e. register in
    the COM's running-object-table).

    Both server types can use Qt either as a shared library, or statically
    linked into the server binary.

    \section2 Typical Errors During the Post-Build Steps

    For the ActiveQt specific post-processing steps to work the 
    server has to meet some requirements:

    \list
    \o All controls exposed can be created with nothing but a QApplication
    instance being present
    \o The initial linking of the server includes a temporary type 
    library resource
    \o All dependencies required to run the server are in the system path 
    (or in the path used by the calling environment; note that Visual 
    Studio has its own set of environment variables listed in the
    Tools|Options|Directories dialog).
    \endlist

    If those requirements are not met one ore more of the following 
    errors are likely to occur:

    \section3 The Server Executable Crashes

    To generate the IDL the widgets exposed as ActiveX controls need to
    be instantiated (the constructor is called). At this point, nothing 
    else but a QApplication object exists. Your widget constructor must 
    not rely on any other objects to be created, e.g. it should check for
    null-pointers.

    To debug your server run it with -dumpidl outputfile and check where
    it crashes.

    Note that no functions of the control are called.

    \section3 The Server Executable Is Not a Valid Win32 Application

    Attaching the type library corrupted the server binary. This is a
    bug in Windows and happens only with release builds.

    The first linking step has to link a dummy type library into the
    executable that can later be replaced by idc. Add a resource file
    with a type library to your project as demonstrated in the examples.

    \section3 "Unable to locate DLL"

    The build system needs to run the server executable to generate
    the interface definition, and to register the server. If a dynamic
    link library the server links against is not in the path this
    might fail (e.g. Visual Studio calls the server using the
    enivronment settings specified in the "Directories" option). Make
    sure that all DLLs required by your server are located in a
    directory that is listed in the path as printed in the error
    message box.

    \section3 "Cannot open file ..."

    The ActiveX server could not shut down properly when the last
    client stopped using it. It usually takes about two seconds for
    the application to terminate, but you might have to use the task
    manager to kill the process (e.g. when a client doesn't release
    the controls properly).

    \section1 Implementing Controls

    To implement a COM object with Qt, create a subclass of QObject
    or any existing QObject subclass. If the class is a subclass of QWidget,
    the COM object will be an ActiveX control.

    \snippet doc/src/snippets/code/doc_src_qaxserver.qdoc 3

    The Q_OBJECT macro is required to provide the meta object information
    about the widget to the ActiveQt framework.

    \snippet doc/src/snippets/code/doc_src_qaxserver.qdoc 4

    Use the Q_CLASSINFO() macro to specify the COM identifiers for the COM
    object. \c ClassID and \c InterfaceID are required, while \c EventsID is
    only necessary when your object has signals. To generate these identifiers,
    use system tools like \c uuidgen or \c guidgen.

    You can specify additional attributes for each of your classes; see 
    \l{Class Information and Tuning} for details.

    \snippet doc/src/snippets/code/doc_src_qaxserver.qdoc 5

    Use the Q_PROPERTY() macro to declare properties for the ActiveX control.

    Declare a standard constructor taking a parent object, and functions, 
    signals and slots like for any QObject subclass.
    \footnote
    If a standard constructor is not present the compiler will issue
    an error "no overloaded function takes 2 parameters" when using
    the default factory through the QAXFACTORY_DEFAULT() macro. If you
    cannot provide a standard constructor you must implement a
    QAxFactory custom factory and call the constructor you have in
    your implementation of QAxFactory::create.
    \endfootnote

    \snippet doc/src/snippets/code/doc_src_qaxserver.qdoc 6

    The ActiveQt framework will expose properties and public slots as ActiveX 
    properties and methods, and signals as ActiveX events, and convert between
    the Qt data types and the equivalent COM data types.

    \section2 Data Types

    The Qt data types that are supported for properties are:

    \table
    \header
    \o Qt data type
    \o COM property
    \row
    \o bool
    \o VARIANT_BOOL
    \row
    \o QString
    \o BSTR
    \row
    \o int
    \o int
    \row
    \o uint
    \o unsigned int
    \row
    \o double
    \o double
    \row
    \o \l qlonglong
    \o CY
    \row
    \o \l qulonglong
    \o CY
    \row
    \o QColor
    \o OLE_COLOR
    \row
    \o QDate
    \o DATE
    \row
    \o QDateTime
    \o DATE
    \row
    \o QTime
    \o DATE
    \row
    \o QFont
    \o IFontDisp*
    \row
    \o QPixmap
    \o IPictureDisp*
    \footnote
    COM cannot marshal IPictureDisp accross process boundaries,
    so QPixmap properties cannot be called for out-of-process servers. You
    can however marshal the image data via e.g. temporary files. See the
    Microsoft 
    \link http://support.microsoft.com/default.aspx?scid=kb;[LN];Q150034 KB article 
    Q150034 \endlink for more information.
    \endfootnote
    \row
    \o QVariant
    \o VARIANT
    \row
    \o QVariantList (same as QList\<QVariant\>)
    \o SAFEARRAY(VARIANT)
    \row
    \o QStringList
    \o SAFEARRAY(BSTR)
    \row
    \o QByteArray
    \o SAFEARRAY(BYTE)
    \row
    \o QRect
    \o User defined type
    \row
    \o QSize
    \o User defined type
    \row
    \o QPoint
    \o User defined type
    \endtable

    The Qt data types that are supported for parameters in signals and
    slots are:
    \table
    \header
    \o Qt data type
    \o COM parameter
    \row
    \o bool
    \o [in] VARIANT_BOOL
    \row
    \o bool&
    \o [in, out] VARIANT_BOOL*
    \row
    \o QString, const QString&
    \o [in] BSTR
    \row
    \o QString&
    \o [in, out] BSTR*
    \row
    \o QString&
    \o [in, out] BSTR*
    \row
    \o int
    \o [in] int
    \row
    \o int&
    \o [in,out] int
    \row
    \o uint
    \o [in] unsigned int
    \row
    \o uint&
    \o [in, out] unsigned int*
    \row
    \o double
    \o [in] double
    \row
    \o double&
    \o [in, out] double*
    \row
    \o QColor, const QColor&
    \o [in] OLE_COLOR
    \row
    \o QColor&
    \o [in, out] OLE_COLOR*
    \row
    \o QDate, const QDate&
    \o [in] DATE
    \row
    \o QDate&
    \o [in, out] DATE*
    \row
    \o QDateTime, const QDateTime&
    \o [in] DATE
    \row
    \o QDateTime&
    \o [in, out] DATE*
    \row
    \o QFont, const QFont&
    \o [in] IFontDisp*
    \row
    \o QFont&
    \o [in, out] IFontDisp**
    \row
    \o QPixmap, const QPixmap&
    \o [in] IPictureDisp*
    \row
    \o QPixmap&
    \o [in, out] IPictureDisp**
    \row
    \o QList\<QVariant\>, const QList\<QVariant\>&
    \o [in] SAFEARRAY(VARIANT)
    \row
    \o QList\<QVariant\>&
    \o [in, out] SAFEARRAY(VARIANT)*
    \row
    \o QStringList, const QStringList&
    \o [in] SAFEARRAY(BSTR)
    \row
    \o QStringList&
    \o [in, out] SAFEARRAY(BSTR)*
    \row
    \o QByteArray, const QByteArray&
    \o [in] SAFEARRAY(BYTE)
    \row
    \o QByteArray&
    \o [in, out] SAFEARRAY(BYTE)*
    \row
    \o QObject*
    \o [in] IDispatch*
    \row
    \o QRect&
    \footnote
    OLE needs to marshal user defined types by reference (ByRef), and cannot 
    marshal them by value (ByVal). This is why const-references and object
    parameters are not supported for QRect, QSize and QPoint. Also note that
    servers with this datatype require Windows 98 or DCOM 1.2 to be installed.
    \endfootnote
    \o [in, out] struct QRect (user defined)
    \row
    \o QSize&
    \o [in, out] struct QSize (user defined)
    \row
    \o QPoint&
    \o [in, out] struct QPoint (user defined)
    \endtable

    Also supported are exported enums and flags (see Q_ENUMS() and
    Q_FLAGS()). The in-parameter types are also supported as
    return values.

    Properties and signals/slots that have parameters using any other
    data types are ignored by the ActiveQt framework.

    \section2 Sub-Objects

    COM objects can have multiple sub-objects that can represent a sub element
    of the COM object. A COM object representing a multi-document spread sheet 
    application can for example provide one sub-object for each spread sheet.

    Any QObject subclass can be used as the type for a sub object in ActiveX, as
    long as it is known to the QAxFactory. Then the type can be used in properties,
    or as the return type or paramter of a slot.

    \section2 Property Notification

    To make the properties bindable for the ActiveX client, use multiple
    inheritance from the QAxBindable class:

    \snippet doc/src/snippets/code/doc_src_qaxserver.qdoc 7

    When implementing the property write functions, use the
    QAxBindable class's requestPropertyChange() and propertyChanged()
    functions to allow ActiveX clients to bind to the control
    properties. 
    \footnote 
    This is not required, but gives the client more control over 
    the ActiveX control.
    \endfootnote

    \section1 Serving Controls