docs/latex/wx/dataobj.tex

   1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   2 %% Name:        dataobj.tex
   3 %% Purpose:     wxDataObject documentation
   4 %% Author:      Vadim Zeitlin
   5 %% Modified by:
   6 %% Created:     18.10.99
   7 %% RCS-ID:      $Id$
   8 %% Copyright:   (c) wxWindows team
   9 %% Licence:     wxWindows licence
  10 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  11
  12 \section{\class{wxDataObject}}\label{wxdataobject}
  13
  14 A wxDataObject represents data that can be copied to or from the clipboard, or
  15 dragged and dropped. The important thing about wxDataObject is that this is a
  16 "smart" piece of data unlike usual "dumb" data containers such as memory
  17 buffers or files. Being "smart" here means that the data object itself should
  18 know what data formats it supports and how to render itself in each of
  19 supported formats.
  20
  21 A supported format, incidentally, is exactly the format in which the data can
  22 be requested from a data object or from which the data object may be set. In
  23 the general case, an object may support different formats on "input" and
  24 "output", i.e. it may be able to render itself in a given format but not be
  25 created from data on this format or vice versa. wxDataObject defines an
  26 enumeration type
  27
  28 \begin{verbatim}
  29 enum Direction
  30 {
  31     Get  = 0x01,    // format is supported by GetDataHere()
  32     Set  = 0x02     // format is supported by SetData()
  33 };
  34 \end{verbatim}
  35
  36 which allows to distinguish between them. See
  37 \helpref{wxDataFormat}{wxdataformat} documentation for more about formats.
  38
  39 Not surprizingly, being "smart" comes at a price of added complexity. This is
  40 reasonable for the situations when you really need to support multiple formats,
  41 but may be annoying if you only want to do something simple like cut and paste
  42 text.
  43
  44 To provide a solution for both cases, wxWindows has two predefined classes
  45 which derive from wxDataObject:
  46 \helpref{wxDataObjectSimple}{wxdataobjectsimple} and
  47 \helpref{wxDataObjectComposite}{wxdataobjectcomposite}.
  48 \helpref{wxDataObjectSimple}{wxdataobjectsimple} is
  49 the simplest wxDataObject possible and only holds data in a single format (such
  50 as HTML or text) and \helpref{wxDataObjectComposite}{wxdataobjectcomposite} is
  51 the simplest way to implement wxDataObject which does support multiple formats
  52 because it achievs this by simply holding several wxDataObjectSimple objects.
  53
  54 So, you have several solutions when you need a wxDataObject class (and you need
  55 one as soon as you want to transfer data via the clipboard or drag and drop):
  56
  57 \begin{twocollist}
  58 \twocolitem{0. Use one of built-in classes}{You may use wxTextDataObject,
  59 wxBitmapDataObject or wxFileDataObject in the simplest cases when you only need
  60 to support one format and your data is either text, bitmap or list of files}
  61 \twocolitem{1. Derive your class from wxDataObjectSimple}{This is the simplest
  62 solution for custom data - you will only support one format and so probably
  63 won't be able to communicate with other programs, but data transfer will work
  64 in your program (or between different copies of it).}
  65 \twocolitem{2. Use wxDataObjectComposite}{This is a quite simple, but rather
  66 powerful solution which allows you to support any number of formats (either
  67 standard or custom if you combine it with the previous solution).}
  68 \twocolitem{3. Derive from wxDataObject directly}{This is the solution of
  69 maximal flexibility and efficiency, but it also is the most difficult to
  70 implement.}
  71 \end{twocollist}
  72
  73 Please note that the easiest way to use Drag'n'Drop and the clipboard with
  74 multiple formats is by using wxDataObjectComposite, but it is not the most
  75 efficient one as each wxDataObjectSimple would contain the whole data in its
  76 respective formars. Now imagine that you want to paste 200 pages of text in
  77 your proprietary format, as well as Word, RTF, HTML, Unicode and plain text to
  78 the clipboard and even today's computers are in trouble. For this case, you
  79 will have to derive from wxDataObject directly and make it enumerate its
  80 formats and provide the data in the requested format on demand.
  81
  82 Note that neither the GTK data transfer mechanisms for the clipboard and
  83 Drag'n'Drop nor the OLE data transfer copies any data until another application
  84 actually requests the data. This is in contrast to the "feel" offered to the
  85 user of a program who would normally think that the data resides in the
  86 clipboard after having pressed "Copy" - in reality it is only declared to be
  87 available.
  88
  89 There are several predefined data object classes derived from
  90 wxDataObjectSimple: \helpref{wxFileDataObject}{wxfiledataobject},
  91 \helpref{wxTextDataObject}{wxtextdataobject} and
  92 \helpref{wxBitmapDataObject}{wxbitmapdataobject} which can be used without
  93 change.
  94
  95 You may also derive your own data object classes from
  96 \helpref{wxCustomDataObject}{wxprivatedataobject} for user-defined types. The
  97 format of user-defined data is given as mime-type string literal, such as
  98 "application/word" or "image/png". These strings are used as they are under
  99 Unix (so far only GTK) to identify a format and are translated into their
 100 Windows equivalent under Win32 (using the OLE IDataObject for data exchange to
 101 and from the clipboard and for Drag'n'Drop). Note that the format string
 102 translation under Windows is not yet finnished.
 103
 104 \wxheading{Virtual functions to override}
 105
 106 Each class derived directly from wxDataObject must override and implement all
 107 of its functions which are pure virtual in the base class.
 108
 109 The data objects which only render their data or only set it (i.e. work in
 110 only one direction), should return 0 from
 111 \helpref{GetFormatCount}{wxdataobjectgetformatcount}.
 112
 113 \wxheading{Derived from}
 114
 115 None
 116
 117 \wxheading{Include files}
 118
 119 <wx/dataobj.h>
 120
 121 \wxheading{See also}
 122
 123 \helpref{Clipboard and drag and drop overview}{wxclipboardonfigoverview},
 124 \helpref{DnD sample}{samplednd},
 125 \helpref{wxFileDataObject}{wxfiledataobject},
 126 \helpref{wxTextDataObject}{wxtextdataobject},
 127 \helpref{wxBitmapDataObject}{wxbitmapdataobject},
 128 \helpref{wxPrivateDataObject}{wxprivatedataobject},
 129 \helpref{wxDropTarget}{wxdroptarget},
 130 \helpref{wxDropSource}{wxdropsource},
 131 \helpref{wxTextDropTarget}{wxtextdroptarget},
 132 \helpref{wxFileDropTarget}{wxfiledroptarget}
 133
 134 \latexignore{\rtfignore{\wxheading{Members}}}
 135
 136 \membersection{wxDataObject::wxDataObject}\label{wxdataobjectwxdataobject}
 137
 138 \func{}{wxDataObject}{\void}
 139
 140 Constructor.
 141
 142 \membersection{wxDataObject::\destruct{wxDataObject}}\label{wxdataobjectdtor}
 143
 144 \func{}{\destruct{wxDataObject}}{\void}
 145
 146 Destructor.
 147
 148 \membersection{wxDataObject::GetAllFormats}\label{wxdataobjectgetallformats}
 149
 150 \constfunc{virtual void}{GetAllFormats}{
 151     \param{wxDataFormat *}{formats},
 152     \param{Direction}{ dir = Get}}
 153
 154 Copy all supported formats in the given direction to the array pointed to by
 155 {\it formats} (there is enough place for GetFormatCount(dir) formats in it).
 156
 157 \membersection{wxDataObject::GetDataHere}\label{wxdataobjectgetdatahere}
 158
 159 \constfunc{virtual bool}{GetDataHere}{\param{const wxDataFormat\&}{ format}, \param{void }{*buf} }
 160
 161 The method will write the data of the format {\it format} in the buffer {\it
 162 buf} and return TRUE on success, FALSE on failure.
 163
 164 \membersection{wxDataObject::GetDataSize}\label{wxdataobjectgetdatasize}
 165
 166 \constfunc{virtual size\_t}{GetDataSize}{\param{const wxDataFormat\&}{ format} }
 167
 168 Returns the data size of the given format {\it format}.
 169
 170 \membersection{wxDataObject::GetFormatCount}\label{wxdataobjectgetformatcount}
 171
 172 \constfunc{virtual size\_t}{GetFormatCount}{\param{Direction}{ dir = Get}}
 173
 174 Return the number of available formats for rendering or setting the data.
 175
 176 \membersection{wxDataObject::GetPreferredFormat}\label{wxdataobjectgetpreferredformat}
 177
 178 \constfunc{virtual wxDataFormat}{GetPreferredFormat}{\param{Direction}{ dir = Get}}
 179
 180 Returns the preferred format for either rendering the data (if {\it dir} is
 181 {\tt Get}, its default value) or for setting it. Usually this will be the
 182 native format of the wxDataObject.
 183
 184 \membersection{wxDataObject::SetData}\label{wxdataobjectsetdata}
 185
 186 \func{virtual bool}{SetData}{
 187     \param{const wxDataFormat\&}{ format},
 188     \param{size\_t}{ len},
 189     \param{const void }{*buf} }
 190
 191 Set the data in the format {\it format} of the length {\it len} provided in the
 192 buffer {\it buf}.
 193
 194 Returns TRUE on sucess, FALSE on failure.
 195
 196