source: trunk/doc/src/frameworks-technologies/activeqt-server.qdoc@ 846

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/*!
    \page activeqt-server.html
    \title Building ActiveX servers in Qt
    \ingroup qt-activex

    \brief A Windows-only static library for turning a 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{ActiveQt Examples}{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

    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