wxWidgets/interface/dataobj.h

/////////////////////////////////////////////////////////////////////////////
// Name:        dataobj.h
// Purpose:     documentation for wxCustomDataObject class
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

/**
    @class wxCustomDataObject
    @wxheader{dataobj.h}

    wxCustomDataObject is a specialization of
    wxDataObjectSimple for some
    application-specific data in arbitrary (either custom or one of the standard
    ones). The only restriction is that it is supposed that this data can be
    copied bitwise (i.e. with @c memcpy()), so it would be a bad idea to make
    it contain a C++ object (though C struct is fine).

    By default, wxCustomDataObject stores the data inside in a buffer. To put the
    data into the buffer you may use either
    wxCustomDataObject::SetData or
    wxCustomDataObject::TakeData depending on whether you want
    the object to make a copy of data or not.

    If you already store the data in another place, it may be more convenient and
    efficient to provide the data on-demand which is possible too if you override
    the virtual functions mentioned below.

    @library{wxcore}
    @category{dnd}

    @seealso
    wxDataObject
*/
class wxCustomDataObject : public wxDataObjectSimple
{
public:
    /**
        The constructor accepts a @a format argument which specifies the (single)
        format supported by this object. If it isn't set here,
        wxDataObjectSimple::SetFormat should be used.
    */
    wxCustomDataObject(const wxDataFormat& format = wxFormatInvalid);

    /**
        The destructor will free the data hold by the object. Notice that although it
        calls a virtual Free() function, the base
        class version will always be called (C++ doesn't allow calling virtual
        functions from constructors or destructors), so if you override @c Free(), you
        should override the destructor in your class as well (which would probably
        just call the derived class' version of @c Free()).
    */
    ~wxCustomDataObject();

    /**
        This function is called to allocate @a size bytes of memory from SetData().
        The default version just uses the operator new.
    */
    virtual void* Alloc(size_t size);

    /**
        This function is called when the data is freed, you may override it to anything
        you want (or may be nothing at all). The default version calls operator
        delete[] on the data.
    */
    virtual void Free();

    /**
        Returns a pointer to the data.
    */
    virtual void* GetData() const;

    /**
        Returns the data size in bytes.
    */
    virtual size_t GetSize() const;

    /**
        Set the data. The data object will make an internal copy.
    */
    virtual void SetData(size_t size, const void data);

    /**
        Like SetData(), but doesn't copy the data -
        instead the object takes ownership of the pointer.
        @b wxPython note: This method expects a string in wxPython.  You can pass
        nearly any object by pickling it first.
    */
    virtual void TakeData(size_t size, const void data);
};


/**
    @class wxDataObjectComposite
    @wxheader{dataobj.h}

    wxDataObjectComposite is the simplest
    wxDataObject derivation which may be used to support
    multiple formats. It contains several
    wxDataObjectSimple objects and supports any
    format supported by at least one of them. Only one of these data objects is
    @e preferred (the first one if not explicitly changed by using the second
    parameter of wxDataObjectComposite::Add) and its format determines
    the preferred format of the composite data object as well.

    See wxDataObject documentation for the reasons why you
    might prefer to use wxDataObject directly instead of wxDataObjectComposite for
    efficiency reasons.

    @library{wxcore}
    @category{FIXME}

    @seealso
    @ref overview_wxdndoverview "Clipboard and drag and drop overview",
    wxDataObject, wxDataObjectSimple, wxFileDataObject, wxTextDataObject, wxBitmapDataObject
*/
class wxDataObjectComposite : public wxDataObject
{
public:
    /**
        The default constructor.
    */
    wxDataObjectComposite();

    /**
        Adds the @a dataObject to the list of supported objects and it becomes the
        preferred object if @a preferred is @true.
    */
    void Add(wxDataObjectSimple dataObject, bool preferred = false);

    /**
        Report the format passed to the SetData method.  This should be the
        format of the data object within the composite that recieved data from
        the clipboard or the DnD operation.  You can use this method to find
        out what kind of data object was recieved.
    */
    wxDataFormat GetReceivedFormat() const;
};


/**
    @class wxDataObjectSimple
    @wxheader{dataobj.h}

    This is the simplest possible implementation of the
    wxDataObject class. The data object of (a class derived
    from) this class only supports one format, so the number of virtual functions
    to be implemented is reduced.

    Notice that this is still an abstract base class and cannot be used but should
    be derived from.

    @b wxPython note: If you wish to create a derived wxDataObjectSimple class in
    wxPython you should derive the class from wxPyDataObjectSimple
    in order to get Python-aware capabilities for the various virtual
    methods.

    @b wxPerl note: In wxPerl, you need to derive your data object class
    from Wx::PlDataObjectSimple.

    @library{wxcore}
    @category{FIXME}

    @seealso
    @ref overview_wxdndoverview "Clipboard and drag and drop overview", @ref
    overview_samplednd "DnD sample", wxFileDataObject, wxTextDataObject, wxBitmapDataObject
*/
class wxDataObjectSimple : public wxDataObject
{
public:
    /**
        Constructor accepts the supported format (none by default) which may also be
        set later with SetFormat().
    */
    wxDataObjectSimple(const wxDataFormat& format = wxFormatInvalid);

    /**
        Copy the data to the buffer, return @true on success. Must be implemented in the
        derived class if the object supports rendering its data.
    */
    virtual bool GetDataHere(void buf) const;

    /**
        Gets the size of our data. Must be implemented in the derived class if the
        object supports rendering its data.
    */
    virtual size_t GetDataSize() const;

    /**
        Returns the (one and only one) format supported by this object. It is supposed
        that the format is supported in both directions.
    */
    const wxDataFormat GetFormat() const;

    /**
        Copy the data from the buffer, return @true on success. Must be implemented in
        the derived class if the object supports setting its data.
        @b wxPython note: When implementing this method in wxPython, the data comes
        as a single string parameter rather than the two shown here.
    */
    virtual bool SetData(size_t len, const void buf);

    /**
        Sets the supported format.
    */
    void SetFormat(const wxDataFormat& format);
};


/**
    @class wxBitmapDataObject
    @wxheader{dataobj.h}

    wxBitmapDataObject is a specialization of wxDataObject for bitmap data. It can
    be used without change to paste data into the
    wxClipboard or a wxDropSource. A
    user may wish to derive a new class from this class for providing a bitmap
    on-demand in order to minimize memory consumption when offering data in several
    formats, such as a bitmap and GIF.

    @b wxPython note: If you wish to create a derived wxBitmapDataObject class in
    wxPython you should derive the class from wxPyBitmapDataObject
    in order to get Python-aware capabilities for the various virtual
    methods.

    @library{wxcore}
    @category{dnd}

    @seealso
    @ref overview_wxdndoverview "Clipboard and drag and drop overview",
    wxDataObject, wxDataObjectSimple, wxFileDataObject, wxTextDataObject, wxDataObject
*/
class wxBitmapDataObject : public wxDataObjectSimple
{
public:
    /**
        Constructor, optionally passing a bitmap (otherwise use
        SetBitmap() later).
    */
    wxBitmapDataObject(const wxBitmap& bitmap = wxNullBitmap);

    /**
        Returns the bitmap associated with the data object. You may wish to override
        this method when offering data on-demand, but this is not required by
        wxWidgets' internals. Use this method to get data in bitmap form from
        the wxClipboard.
    */
    virtual wxBitmap GetBitmap() const;

    /**
        Sets the bitmap associated with the data object. This method is called when the
        data object receives data. Usually there will be no reason to override this
        function.
    */
    virtual void SetBitmap(const wxBitmap& bitmap);
};


/**
    @class wxDataFormat
    @wxheader{dataobj.h}

    A wxDataFormat is an encapsulation of a platform-specific format handle which
    is used by the system for the clipboard and drag and drop operations. The
    applications are usually only interested in, for example, pasting data from the
    clipboard only if the data is in a format the program understands and a data
    format is something which uniquely identifies this format.

    On the system level, a data format is usually just a number (@c CLIPFORMAT
    under Windows or @c Atom under X11, for example) and the standard formats
    are, indeed, just numbers which can be implicitly converted to wxDataFormat.
    The standard formats are:



    wxDF_INVALID


    An invalid format - used as default argument for
    functions taking a wxDataFormat argument sometimes


    wxDF_TEXT


    Text format (wxString)


    wxDF_BITMAP


    A bitmap (wxBitmap)


    wxDF_METAFILE


    A metafile (wxMetafile, Windows only)


    wxDF_FILENAME


    A list of filenames


    wxDF_HTML


    An HTML string. This is only valid when passed to wxSetClipboardData
    when compiled with Visual C++ in non-Unicode mode



    As mentioned above, these standard formats may be passed to any function taking
    wxDataFormat argument because wxDataFormat has an implicit conversion from
    them (or, to be precise from the type @c wxDataFormat::NativeFormat which is
    the type used by the underlying platform for data formats).

    Aside the standard formats, the application may also use custom formats which
    are identified by their names (strings) and not numeric identifiers. Although
    internally custom format must be created (or @e registered) first, you
    shouldn't care about it because it is done automatically the first time the
    wxDataFormat object corresponding to a given format name is created. The only
    implication of this is that you should avoid having global wxDataFormat objects
    with non-default constructor because their constructors are executed before the
    program has time to perform all necessary initialisations and so an attempt to
    do clipboard format registration at this time will usually lead to a crash!

    @library{wxbase}
    @category{dnd}

    @seealso
    @ref overview_wxdndoverview "Clipboard and drag and drop overview", @ref
    overview_samplednd "DnD sample", wxDataObject
*/
class wxDataFormat
{
public:
    /**
        Constructs a data format object for a custom format identified by its name
        @e format.
    */
    wxDataFormat(const wxChar format);

    /**
        Returns the name of a custom format (this function will fail for a standard
        format).
    */
    wxString GetId() const;

    /**
        Returns the platform-specific number identifying the format.
    */
    NativeFormat GetType() const;

    /**
        Sets the format to be the custom format identified by the given name.
    */
    void SetId(const wxChar format);

    /**
        Sets the format to the given value, which should be one of wxDF_XXX constants.
    */
    void SetType(NativeFormat format);

    /**
        Returns @true if the formats are different.
    */
    bool operator !=(const wxDataFormat& format) const;

    /**
        Returns @true if the formats are equal.
    */
    bool operator ==(const wxDataFormat& format) const;
};


/**
    @class wxURLDataObject
    @wxheader{dataobj.h}

    wxURLDataObject is a wxDataObject containing an URL
    and can be used e.g. when you need to put an URL on or retrieve it from the
    clipboard:

    @code
    wxTheClipboard-SetData(new wxURLDataObject(url));
    @endcode

    @library{wxcore}
    @category{dnd}

    @seealso
    @ref overview_wxdndoverview "Clipboard and drag and drop overview", wxDataObject
*/
class wxURLDataObject
{
public:
    /**
        Constructor, may be used to initialize the URL. If @a url is empty,
        SetURL() can be used later.
    */
    wxURLDataObject(const wxString& url = wxEmptyString);

    /**
        Returns the URL stored by this object, as a string.
    */
    wxString GetURL() const;

    /**
        Sets the URL stored by this object.
    */
    void SetURL(const wxString& url);
};


/**
    @class wxDataObject
    @wxheader{dataobj.h}

    A wxDataObject represents data that can be copied to or from the clipboard, or
    dragged and dropped. The important thing about wxDataObject is that this is a
    'smart' piece of data unlike 'dumb' data containers such as memory
    buffers or files. Being 'smart' here means that the data object itself should
    know what data formats it supports and how to render itself in each of
    its supported formats.

    A supported format, incidentally, is exactly the format in which the data can
    be requested from a data object or from which the data object may be set. In
    the general case, an object may support different formats on 'input' and
    'output', i.e. it may be able to render itself in a given format but not be
    created from data on this format or vice versa. wxDataObject defines an
    enumeration type

    @code
    enum Direction
    {
        Get  = 0x01,    // format is supported by GetDataHere()
        Set  = 0x02     // format is supported by SetData()
    };
    @endcode

    which distinguishes between them. See
    wxDataFormat documentation for more about formats.

    Not surprisingly, being 'smart' comes at a price of added complexity. This is
    reasonable for the situations when you really need to support multiple formats,
    but may be annoying if you only want to do something simple like cut and paste
    text.

    To provide a solution for both cases, wxWidgets has two predefined classes
    which derive from wxDataObject: wxDataObjectSimple and
    wxDataObjectComposite.
    wxDataObjectSimple is
    the simplest wxDataObject possible and only holds data in a single format (such
    as HTML or text) and wxDataObjectComposite is
    the simplest way to implement a wxDataObject that does support multiple formats
    because it achieves this by simply holding several wxDataObjectSimple objects.

    So, you have several solutions when you need a wxDataObject class (and you need
    one as soon as you want to transfer data via the clipboard or drag and drop):



    @b 1. Use one of the built-in classes


    You may use wxTextDataObject,
    wxBitmapDataObject or wxFileDataObject in the simplest cases when you only need
    to support one format and your data is either text, bitmap or list of files.


    @b 2. Use wxDataObjectSimple


    Deriving from wxDataObjectSimple is the simplest
    solution for custom data - you will only support one format and so probably
    won't be able to communicate with other programs, but data transfer will work
    in your program (or between different copies of it).


    @b 3. Use wxDataObjectComposite


    This is a simple but powerful
    solution which allows you to support any number of formats (either
    standard or custom if you combine it with the previous solution).


    @b 4. Use wxDataObject directly


    This is the solution for
    maximal flexibility and efficiency, but it is also the most difficult to
    implement.



    Please note that the easiest way to use drag and drop and the clipboard with
    multiple formats is by using wxDataObjectComposite, but it is not the most
    efficient one as each wxDataObjectSimple would contain the whole data in its
    respective formats. Now imagine that you want to paste 200 pages of text in
    your proprietary format, as well as Word, RTF, HTML, Unicode and plain text to
    the clipboard and even today's computers are in trouble. For this case, you
    will have to derive from wxDataObject directly and make it enumerate its
    formats and provide the data in the requested format on demand.

    Note that neither the GTK+ data transfer mechanisms for clipboard and
    drag and drop, nor OLE data transfer, copy any data until another application
    actually requests the data. This is in contrast to the 'feel' offered to the
    user of a program who would normally think that the data resides in the
    clipboard after having pressed 'Copy' - in reality it is only declared to be
    available.

    There are several predefined data object classes derived from
    wxDataObjectSimple: wxFileDataObject,
    wxTextDataObject,
    wxBitmapDataObject and
    wxURLDataObject
    which can be used without change.

    You may also derive your own data object classes from
    wxCustomDataObject for user-defined types. The
    format of user-defined data is given as a mime-type string literal, such as
    "application/word" or "image/png". These strings are used as they are under
    Unix (so far only GTK+) to identify a format and are translated into their
    Windows equivalent under Win32 (using the OLE IDataObject for data exchange to
    and from the clipboard and for drag and drop). Note that the format string
    translation under Windows is not yet finished.

    @b wxPython note: At this time this class is not directly usable from wxPython.
    Derive a class from wxPyDataObjectSimple
    instead.

    @b wxPerl note: This class is not currently usable from wxPerl; you may
    use Wx::PlDataObjectSimple instead.

    @library{wxcore}
    @category{dnd}

    @seealso
    @ref overview_wxdndoverview "Clipboard and drag and drop overview", @ref
    overview_samplednd "DnD sample", wxFileDataObject, wxTextDataObject, wxBitmapDataObject, wxCustomDataObject, wxDropTarget, wxDropSource, wxTextDropTarget, wxFileDropTarget
*/
class wxDataObject
{
public:
    /**
        Constructor.
    */
    wxDataObject();

    /**
        Destructor.
    */
    ~wxDataObject();

    /**
        Copy all supported formats in the given direction to the array pointed to by
        @e formats. There is enough space for GetFormatCount(dir) formats in it.
    */
    virtual void GetAllFormats(wxDataFormat* formats,
                               Direction dir = Get) const;

    /**
        The method will write the data of the format @a format in the buffer @a buf and
        return @true on success, @false on failure.
    */
    virtual bool GetDataHere(const wxDataFormat& format, void buf) const;

    /**
        Returns the data size of the given format @e format.
    */
    virtual size_t GetDataSize(const wxDataFormat& format) const;

    /**
        Returns the number of available formats for rendering or setting the data.
    */
    virtual size_t GetFormatCount(Direction dir = Get) const;

    /**
        Returns the preferred format for either rendering the data (if @a dir is @c Get,
        its default value) or for setting it. Usually this will be the
        native format of the wxDataObject.
    */
    virtual wxDataFormat GetPreferredFormat(Direction dir = Get) const;

    /**
        Set the data in the format @a format of the length @a len provided in the
        buffer @e buf.
        Returns @true on success, @false on failure.
    */
    virtual bool SetData(const wxDataFormat& format, size_t len,
                         const void buf);
};


/**
    @class wxTextDataObject
    @wxheader{dataobj.h}

    wxTextDataObject is a specialization of wxDataObject for text data. It can be
    used without change to paste data into the wxClipboard
    or a wxDropSource. A user may wish to derive a new
    class from this class for providing text on-demand in order to minimize memory
    consumption when offering data in several formats, such as plain text and RTF
    because by default the text is stored in a string in this class, but it might
    as well be generated when requested. For this,
    wxTextDataObject::GetTextLength and
    wxTextDataObject::GetText will have to be overridden.

    Note that if you already have the text inside a string, you will not achieve
    any efficiency gain by overriding these functions because copying wxStrings is
    already a very efficient operation (data is not actually copied because
    wxStrings are reference counted).

    @b wxPython note: If you wish to create a derived wxTextDataObject class in
    wxPython you should derive the class from wxPyTextDataObject
    in order to get Python-aware capabilities for the various virtual
    methods.

    @library{wxcore}
    @category{dnd}

    @seealso
    @ref overview_wxdndoverview "Clipboard and drag and drop overview",
    wxDataObject, wxDataObjectSimple, wxFileDataObject, wxBitmapDataObject
*/
class wxTextDataObject : public wxDataObjectSimple
{
public:
    /**
        Constructor, may be used to initialise the text (otherwise
        SetText() should be used later).
    */
    wxTextDataObject(const wxString& text = wxEmptyString);

    /**
        Returns the text associated with the data object. You may wish to override
        this method when offering data on-demand, but this is not required by
        wxWidgets' internals. Use this method to get data in text form from
        the wxClipboard.
    */
    virtual wxString GetText() const;

    /**
        Returns the data size. By default, returns the size of the text data
        set in the constructor or using SetText().
        This can be overridden to provide text size data on-demand. It is recommended
        to return the text length plus 1 for a trailing zero, but this is not
        strictly required.
    */
    virtual size_t GetTextLength() const;

    /**
        Sets the text associated with the data object. This method is called
        when the data object receives the data and, by default, copies the text into
        the member variable. If you want to process the text on the fly you may wish to
        override this function.
    */
    virtual void SetText(const wxString& strText);
};


/**
    @class wxFileDataObject
    @wxheader{dataobj.h}

    wxFileDataObject is a specialization of wxDataObject
    for file names. The program works with it just as if it were a list of absolute
    file
    names, but internally it uses the same format as
    Explorer and other compatible programs under Windows or GNOME/KDE filemanager
    under Unix which makes it possible to receive files from them using this
    class.

    @b Warning: Under all non-Windows platforms this class is currently
    "input-only", i.e. you can receive the files from another application, but
    copying (or dragging) file(s) from a wxWidgets application is not currently
    supported. PS: GTK2 should work as well.

    @library{wxcore}
    @category{dnd}

    @seealso
    wxDataObject, wxDataObjectSimple, wxTextDataObject, wxBitmapDataObject,
    wxDataObject
*/
class wxFileDataObject : public wxDataObjectSimple
{
public:
    /**
        Constructor.
    */
    wxFileDataObject();

    /**
        @b MSW only: adds a file to the file list represented by this data object.
    */
    virtual void AddFile(const wxString& file);

    /**
        Returns the array of file names.
    */
    const wxArrayString GetFilenames() const;
};