docs/doxygen/overviews/dnd.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        dnd
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /*!
  10
  11  @page dnd_overview Drag and drop overview
  12
  13  Classes: #wxDataObject,
  14  #wxTextDataObject,
  15  #wxDropSource,
  16  #wxDropTarget,
  17  #wxTextDropTarget,
  18  #wxFileDropTarget
  19  Note that wxUSE_DRAG_AND_DROP must be defined in setup.h in order
  20  to use drag and drop in wxWidgets.
  21  See also: @ref dataobject_overview and @ref samplednd_overview
  22  It may be noted that data transfer to and from the clipboard is quite
  23  similar to data transfer with drag and drop and the code to implement
  24  these two types is almost the same. In particular, both data transfer
  25  mechanisms store data in some kind of #wxDataObject
  26  and identify its format(s) using the #wxDataFormat
  27  class.
  28  To be a @e drag source, i.e. to provide the data which may be dragged by
  29  the user elsewhere, you should implement the following steps:
  30
  31
  32   @b Preparation: First of all, a data object must be created and
  33  initialized with the data you wish to drag. For example:
  34
  35  @code
  36  wxTextDataObject my_data("This text will be dragged.");
  37  @endcode
  38
  39  @b Drag start: To start the dragging process (typically in response to a
  40  mouse click) you must call wxDropSource::DoDragDrop
  41  like this:
  42
  43  @code
  44  wxDropSource dragSource( this );
  45   dragSource.SetData( my_data );
  46   wxDragResult result = dragSource.DoDragDrop( TRUE );
  47  @endcode
  48
  49   @b Dragging: The call to DoDragDrop() blocks the program until the user releases the
  50  mouse button (unless you override the #GiveFeedback function
  51  to do something special). When the mouse moves in a window of a program which understands the
  52  same drag-and-drop protocol (any program under Windows or any program supporting the
  53  XDnD protocol under X Windows), the corresponding #wxDropTarget methods
  54  are called - see below.
  55   @b Processing the result: DoDragDrop() returns an @e effect code which
  56  is one of the values of @c wxDragResult enum (explained #here):
  57
  58  @code
  59  switch (result)
  60   {
  61       case wxDragCopy: /* copy the data */ break;
  62 case wxDragMove: /* move the data */
  63 break;
  64 default:         /* do nothing */
  65 break;
  66 }
  67 @endcode
  68
  69
  70
  71 To be a @e drop target, i.e. to receive the data dropped by the user you should
  72 follow the instructions below:
  73
  74
  75 @b Initialization: For a window to be a drop target, it needs to have
  76 an associated #wxDropTarget object. Normally, you will
  77 call wxWindow::SetDropTarget during window
  78 creation associating your drop target with it. You must derive a class from
  79             wxDropTarget and override its pure virtual methods. Alternatively, you may
  80             derive from #wxTextDropTarget or
  81 #wxFileDropTarget and override their OnDropText()
  82             or OnDropFiles() method.
  83             @b Drop: When the user releases the mouse over a window, wxWidgets
  84             asks the associated wxDropTarget object if it accepts the data. For this,
  85             a #wxDataObject must be associated with the drop target
  86             and this data object will be responsible for the format negotiation between
  87                 the drag source and the drop target. If all goes well, then #OnData
  88                 will get called and the wxDataObject belonging to the drop target can get
  89                 filled with data.
  90                 @b The end: After processing the data, DoDragDrop() returns either
  91                     wxDragCopy or wxDragMove depending on the state of the keys Ctrl, Shift
  92                     and Alt at the moment of the drop. There is currently no way for the drop
  93                     target to change this return code.
  94
  95                                                  */
  96
  97