docs/latex/wx/tclipbrd.tex

   1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   2 %% Name:        tclipbrd.tex
   3 %% Purpose:     Data transfer (clipboard and drag and drop) overview
   4 %% Author:      Vadim Zeitlin
   5 %% Modified by:
   6 %% Created:     18.10.99
   7 %% RCS-ID:      $Id$
   8 %% Copyright:   (c) Vadim Zeitlin
   9 %% Licence:     wxWindows licence
  10 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  11
  12 \section{Clipboard and drag and drop overview}\label{wxclipboardonfigoverview}
  13
  14 Classes: \helpref{wxDataObject}{wxdataobject},
  15          \helpref{wxClipboard}{wxclipboard},
  16          \helpref{wxDataFormat}{wxdataformat},
  17          \helpref{wxDropSource}{wxdropsource},
  18          \helpref{wxDropTarget}{wxdroptarget}
  19
  20 This overview discusses data transfer through clipboard or drag and drop. In
  21 wxWindows, these two ways to transfer data (either between different
  22 applications or inside one and the same) are very similar which allows to
  23 implement both of them using almost the same code - or, to say it in other
  24 words, if you implement drag and drop support for your application, you get
  25 clipboard support for free and vice versa.
  26
  27 In the heart of both clipboard and drag and drop operations lies the
  28 \helpref{wxDataObject}{wxdataobject} class. The objects of this (or, to be
  29 precise, derived from it) class represent the data which is being carried by
  30 the mouse during drag and drop operation or copied to or pasted from the
  31 clipboard. \helpref{wxDataObject}{wxdataobject} is a "smart" piece of data
  32 because it knows which \helpref{formats}{wxdataformat} it supports (see
  33 \helpref{GetFormatCount}{wxdataobjectgetformatcount} and
  34 \helpref{GetAllFormats}{wxdataobjectgetallformats}) and knows how to render
  35 itself in any of them (see \helpref{GetDataHere.}{wxdataobjectgetdatahere}).
  36 It can also receive its value from the outside in a format it supports if it
  37 implements \helpref{SetData}{wxdataobjectsetdata} method.
  38
  39 Both clipboard and drag and drop operations have two sides: the source and
  40 target, the data provider and the data receiver (which may be the same
  41 application and even the same window when, for example, you drag some text from
  42 one position to another in a word processor). Let us describe what each of them
  43 should do.
  44
  45 \subsection{The data provider (source) duties}{wxdataobjectsource}
  46
  47 The data provider is responsible for creating a
  48 \helpref{wxDataObject}{wxdataobjectwxdataobject} containing the data to be
  49 transfered. Then it should either pass it to the clipboard using
  50 \helpref{AddData}{wxclipboardadddata} or \helpref{SetData}{wxclipboardsetdata}
  51 functions or to \helpref{wxDropSource}{wxdropsource} and call
  52 \helpref{DoDragDrop}{wxdropsourcedodragdrop} function.
  53
  54 The only (but important) difference is that the object for the clipboard
  55 transfer must always be created on the heap (i.e. using {\tt new}) and it will
  56 be freed by the clipboard when it is no longer needed (indeed, it is not known
  57 in advance when, if ever, the data will be pasted from the clipboard). On the
  58 other hand, the object for drag and drop operation must only exist while
  59 \helpref{DoDragDrop}{wxdropsourcedodragdrop} executes and may be safely deleted
  60 afterwards and so can be created either on heap or on stack (i.e. as a local
  61 variable).
  62
  63 Another small difference si that in the case of clipboard operation, the
  64 application usually knows in advance whether it copies or cuts (i.e. copies and
  65 deletes) data - in fact, this usually depends on which menu item the user
  66 chose. But for drag and drop it can only know it after
  67 \helpref{DoDragDrop}{wxdropsourcedodragdrop} returns (from its return value).
  68
  69 \subsection{The data receiver (target) duties}{wxdataobjecttarget}
  70
  71 To receive (paste in usual terminology) data from the clipboard, you should
  72 create a \helpref{wxDataObject}{wxdataobject} derived class which supports the
  73 data formats you need and pass it as argument to
  74 \helpref{wxClipboard::GetData}{wxclipboardgetdata}. If it returns {\tt FALSE},
  75 no data in (any of) the supported format(s) is available. If it returns {\tt
  76 TRUE}, the data has been successfully transfered to wxDataObject.
  77
  78 {\bf TODO} document drag and drop side when the API is finalised