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: \helpref{wxDataObjectSimple}{wxdataobjectsimple} and
  46 \helpref{wxDataObjectComposite}{wxdataobjectcomposite}.
  47 \helpref{wxDataObjectSimple}{wxdataobjectsimple} is
  48 the simplest wxDataObject possible and only holds data in a single format (such
  49 as HTML or text) and \helpref{wxDataObjectComposite}{wxdataobjectcomposite} is
  50 the simplest way to implement wxDataObject which does support multiple formats
  51 because it achievs this by simply holding several wxDataObjectSimple objects.
  52
  53 So, you have several solutions when you need a wxDataObject class (and you need
  54 one as soon as you want to transfer data via the clipboard or drag and drop):
  55
  56 \begin{twocollist}\itemsep=1cm
  57 \twocolitem{{\bf 0. Use one of built-in classes}}{You may use wxTextDataObject,
  58 wxBitmapDataObject or wxFileDataObject in the simplest cases when you only need
  59 to support one format and your data is either text, bitmap or list of files.}
  60 \twocolitem{{\bf 1. Use wxDataObjectSimple}}{Deriving from wxDataObjectSimple is the simplest
  61 solution for custom data - you will only support one format and so probably
  62 won't be able to communicate with other programs, but data transfer will work
  63 in your program (or between different copies of it).}
  64 \twocolitem{{\bf 2. Use wxDataObjectComposite}}{This is a simple but powerful
  65 solution which allows you to support any number of formats (either
  66 standard or custom if you combine it with the previous solution).}
  67 \twocolitem{{\bf 3. Use wxDataObject directly}}{This is the solution for
  68 maximal flexibility and efficiency, but it also is the most difficult to
  69 implement.}
  70 \end{twocollist}
  71
  72 Please note that the easiest way to use drag and drop and the clipboard with
  73 multiple formats is by using wxDataObjectComposite, but it is not the most
  74 efficient one as each wxDataObjectSimple would contain the whole data in its
  75 respective formars. Now imagine that you want to paste 200 pages of text in
  76 your proprietary format, as well as Word, RTF, HTML, Unicode and plain text to
  77 the clipboard and even today's computers are in trouble. For this case, you
  78 will have to derive from wxDataObject directly and make it enumerate its
  79 formats and provide the data in the requested format on demand.
  80
  81 Note that neither the GTK data transfer mechanisms for the clipboard and
  82 drag and drop, neither does the OLE data transfer copy any data until another application
  83 actually requests the data. This is in contrast to the 'feel' offered to the
  84 user of a program who would normally think that the data resides in the
  85 clipboard after having pressed 'Copy' - in reality it is only declared to be
  86 available.
  87
  88 There are several predefined data object classes derived from
  89 wxDataObjectSimple: \helpref{wxFileDataObject}{wxfiledataobject},
  90 \helpref{wxTextDataObject}{wxtextdataobject} and
  91 \helpref{wxBitmapDataObject}{wxbitmapdataobject} which can be used without
  92 change.
  93
  94 You may also derive your own data object classes from
  95 \helpref{wxCustomDataObject}{wxprivatedataobject} for user-defined types. The
  96 format of user-defined data is given as mime-type string literal, such as
  97 "application/word" or "image/png". These strings are used as they are under
  98 Unix (so far only GTK) to identify a format and are translated into their
  99 Windows equivalent under Win32 (using the OLE IDataObject for data exchange to
 100 and from the clipboard and for drag and drop). Note that the format string
 101 translation under Windows is not yet finished.
 102
 103 \wxheading{Virtual functions to override}
 104
 105 Each class derived directly from wxDataObject must override and implement all
 106 of its functions which are pure virtual in the base class.
 107
 108 The data objects which only render their data or only set it (i.e. work in
 109 only one direction), should return 0 from
 110 \helpref{GetFormatCount}{wxdataobjectgetformatcount}.
 111
 112 \wxheading{Derived from}
 113
 114 None
 115
 116 \wxheading{Include files}
 117
 118 <wx/dataobj.h>
 119
 120 \wxheading{See also}
 121
 122 \helpref{Clipboard and drag and drop overview}{wxdndoverview},
 123 \helpref{DnD sample}{samplednd},
 124 \helpref{wxFileDataObject}{wxfiledataobject},
 125 \helpref{wxTextDataObject}{wxtextdataobject},
 126 \helpref{wxBitmapDataObject}{wxbitmapdataobject},
 127 \helpref{wxPrivateDataObject}{wxprivatedataobject},
 128 \helpref{wxDropTarget}{wxdroptarget},
 129 \helpref{wxDropSource}{wxdropsource},
 130 \helpref{wxTextDropTarget}{wxtextdroptarget},
 131 \helpref{wxFileDropTarget}{wxfiledroptarget}
 132
 133 \latexignore{\rtfignore{\wxheading{Members}}}
 134
 135 \membersection{wxDataObject::wxDataObject}\label{wxdataobjectwxdataobject}
 136
 137 \func{}{wxDataObject}{\void}
 138
 139 Constructor.
 140
 141 \membersection{wxDataObject::\destruct{wxDataObject}}\label{wxdataobjectdtor}
 142
 143 \func{}{\destruct{wxDataObject}}{\void}
 144
 145 Destructor.
 146
 147 \membersection{wxDataObject::GetAllFormats}\label{wxdataobjectgetallformats}
 148
 149 \constfunc{virtual void}{GetAllFormats}{ \param{wxDataFormat *}{formats}, \param{Direction}{ dir = Get}}
 150
 151 Copy all supported formats in the given direction to the array pointed to by
 152 {\it formats}. There is enough space for GetFormatCount(dir) formats in it.
 153
 154 \membersection{wxDataObject::GetDataHere}\label{wxdataobjectgetdatahere}
 155
 156 \constfunc{virtual bool}{GetDataHere}{\param{const wxDataFormat\&}{ format}, \param{void }{*buf} }
 157
 158 The method will write the data of the format {\it format} in the buffer {\it
 159 buf} and return TRUE on success, FALSE on failure.
 160
 161 \membersection{wxDataObject::GetDataSize}\label{wxdataobjectgetdatasize}
 162
 163 \constfunc{virtual size\_t}{GetDataSize}{\param{const wxDataFormat\&}{ format} }
 164
 165 Returns the data size of the given format {\it format}.
 166
 167 \membersection{wxDataObject::GetFormatCount}\label{wxdataobjectgetformatcount}
 168
 169 \constfunc{virtual size\_t}{GetFormatCount}{\param{Direction}{ dir = Get}}
 170
 171 Returns the number of available formats for rendering or setting the data.
 172
 173 \membersection{wxDataObject::GetPreferredFormat}\label{wxdataobjectgetpreferredformat}
 174
 175 \constfunc{virtual wxDataFormat}{GetPreferredFormat}{\param{Direction}{ dir = Get}}
 176
 177 Returns the preferred format for either rendering the data (if {\it dir} is {\tt Get},
 178 its default value) or for setting it. Usually this will be the
 179 native format of the wxDataObject.
 180
 181 \membersection{wxDataObject::SetData}\label{wxdataobjectsetdata}
 182
 183 \func{virtual bool}{SetData}{ \param{const wxDataFormat\&}{ format}, \param{size\_t}{ len}, \param{const void }{*buf} }
 184
 185 Set the data in the format {\it format} of the length {\it len} provided in the
 186 buffer {\it buf}.
 187
 188 Returns TRUE on success, FALSE on failure.
 189