docs/doxygen/overviews/dnd.h

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