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 %% License:     wxWindows license
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  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 1. Use one of the 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 2. 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 3. 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 4. Use wxDataObject directly}}{This is the solution for
  68 maximal flexibility and efficiency, but it is 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 formats. 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, nor 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}{wxcustomdataobject} 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 \pythonnote{At this time this class is not directly usable from wxPython.
 104 Derive a class from \helpref{wxPyDataObjectSimple}{wxdataobjectsimple}
 105 instead.}
 106
 107 \wxheading{Virtual functions to override}
 108
 109 Each class derived directly from wxDataObject must override and implement all
 110 of its functions which are pure virtual in the base class.
 111
 112 The data objects which only render their data or only set it (i.e. work in
 113 only one direction), should return 0 from
 114 \helpref{GetFormatCount}{wxdataobjectgetformatcount}.
 115
 116 \wxheading{Derived from}
 117
 118 None
 119
 120 \wxheading{Include files}
 121
 122 <wx/dataobj.h>
 123
 124 \wxheading{See also}
 125
 126 \helpref{Clipboard and drag and drop overview}{wxdndoverview},
 127 \helpref{DnD sample}{samplednd},
 128 \helpref{wxFileDataObject}{wxfiledataobject},
 129 \helpref{wxTextDataObject}{wxtextdataobject},
 130 \helpref{wxBitmapDataObject}{wxbitmapdataobject},
 131 \helpref{wxCustomDataObject}{wxcustomdataobject},
 132 \helpref{wxDropTarget}{wxdroptarget},
 133 \helpref{wxDropSource}{wxdropsource},
 134 \helpref{wxTextDropTarget}{wxtextdroptarget},
 135 \helpref{wxFileDropTarget}{wxfiledroptarget}
 136
 137 \latexignore{\rtfignore{\wxheading{Members}}}
 138
 139 \membersection{wxDataObject::wxDataObject}\label{wxdataobjectwxdataobject}
 140
 141 \func{}{wxDataObject}{\void}
 142
 143 Constructor.
 144
 145 \membersection{wxDataObject::\destruct{wxDataObject}}\label{wxdataobjectdtor}
 146
 147 \func{}{\destruct{wxDataObject}}{\void}
 148
 149 Destructor.
 150
 151 \membersection{wxDataObject::GetAllFormats}\label{wxdataobjectgetallformats}
 152
 153 \constfunc{virtual void}{GetAllFormats}{ \param{wxDataFormat *}{formats}, \param{Direction}{ dir = Get}}
 154
 155 Copy all supported formats in the given direction to the array pointed to by
 156 {\it formats}. There is enough space for GetFormatCount(dir) formats in it.
 157
 158 \membersection{wxDataObject::GetDataHere}\label{wxdataobjectgetdatahere}
 159
 160 \constfunc{virtual bool}{GetDataHere}{\param{const wxDataFormat\&}{ format}, \param{void }{*buf} }
 161
 162 The method will write the data of the format {\it format} in the buffer {\it
 163 buf} and return TRUE on success, FALSE on failure.
 164
 165 \membersection{wxDataObject::GetDataSize}\label{wxdataobjectgetdatasize}
 166
 167 \constfunc{virtual size\_t}{GetDataSize}{\param{const wxDataFormat\&}{ format} }
 168
 169 Returns the data size of the given format {\it format}.
 170
 171 \membersection{wxDataObject::GetFormatCount}\label{wxdataobjectgetformatcount}
 172
 173 \constfunc{virtual size\_t}{GetFormatCount}{\param{Direction}{ dir = Get}}
 174
 175 Returns the number of available formats for rendering or setting the data.
 176
 177 \membersection{wxDataObject::GetPreferredFormat}\label{wxdataobjectgetpreferredformat}
 178
 179 \constfunc{virtual wxDataFormat}{GetPreferredFormat}{\param{Direction}{ dir = Get}}
 180
 181 Returns the preferred format for either rendering the data (if {\it dir} is {\tt Get},
 182 its default value) or for setting it. Usually this will be the
 183 native format of the wxDataObject.
 184
 185 \membersection{wxDataObject::SetData}\label{wxdataobjectsetdata}
 186
 187 \func{virtual bool}{SetData}{ \param{const wxDataFormat\&}{ format}, \param{size\_t}{ len}, \param{const void }{*buf} }
 188
 189 Set the data in the format {\it format} of the length {\it len} provided in the
 190 buffer {\it buf}.
 191
 192 Returns TRUE on success, FALSE on failure.
 193