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{wxdndoverview}
  13
  14 Classes: \helpref{wxDataObject}{wxdataobject},
  15  \helpref{wxClipboard}{wxclipboard},
  16  \helpref{wxDataFormat}{wxdataformat},
  17  \helpref{wxDropSource}{wxdropsource},
  18  \helpref{wxDropTarget}{wxdroptarget}
  19
  20 See also: \helpref{DnD sample}{samplednd}
  21
  22 This overview discusses data transfer through clipboard or drag and drop. In
  23 wxWindows, these two ways to transfer data (either between different
  24 applications or inside one and the same) are very similar which allows to
  25 implement both of them using almost the same code - or, in other
  26 words, if you implement drag and drop support for your application, you get
  27 clipboard support for free and vice versa.
  28
  29 At the heart of both clipboard and drag and drop operations lies the
  30 \helpref{wxDataObject}{wxdataobject} class. The objects of this class (or, to
  31 be precise, classes derived from it) represent the data which is being carried
  32 by the mouse during drag and drop operation or copied to or pasted from the
  33 clipboard. wxDataObject is a "smart" piece of data because it knows which
  34 formats it supports (see GetFormatCount and GetAllFormats) and knows how to
  35 render itself in any of them (see GetDataHere). It can also receive its value
  36 from the outside in a format it supports if it implements the SetData method.
  37 Please see the documentation of this class for more details.
  38
  39 Both clipboard and drag and drop operations have two sides: the source and
  40 target, the data provider and the data receiver. These which may be in 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}\label{wxdataobjectsource}
  46
  47 The data provider is responsible for creating a
  48 \helpref{wxDataObject}{wxdataobject} containing the data to be
  49 transfered. Then it should either pass it to the clipboard using
  50 \helpref{SetData}{wxclipboardsetdata} function or to
  51 \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 is 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}\label{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 For drag and drop case, the \helpref{wxDropTarget::OnData}{wxdroptargetondata}
  79 virtual function will be called when a data object is dropped, from which the
  80 data itself may be requested by calling
  81 \helpref{wxDropTarget::GetData}{wxdroptargetwxdroptarget} method which fills
  82 the data object.
  83