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 license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_dnd Drag and Drop Overview
  12
  13 Classes: wxDataObject, wxTextDataObject, wxDropSource, wxDropTarget,
  14          wxTextDropTarget, wxFileDropTarget
  15
  16 Note that @c wxUSE_DRAG_AND_DROP must be defined in @c setup.h in order
  17 to use drag and drop in wxWidgets.
  18
  19 See also: @ref overview_dataobject and @ref page_samples_dnd.
  20
  21 It may be noted that data transfer to and from the clipboard is quite
  22 similar to data transfer with drag and drop and the code to implement
  23 these two types is almost the same. In particular, both data transfer
  24 mechanisms store data in some kind of wxDataObject and identify its format(s)
  25 using the wxDataFormat class.
  26
  27 To be a @e drag source, i.e. to provide the data which may be dragged by
  28 the user elsewhere, you should implement the following steps:
  29
  30 @li @b Preparation: First of all, a data object must be created and
  31     initialized with the data you wish to drag. For example:
  32
  33     @code
  34     wxTextDataObject my_data("This text will be dragged.");
  35     @endcode
  36
  37 @li <b>Drag start</b>: To start the dragging process (typically in response to a
  38     mouse click) you must call wxDropSource::DoDragDrop like this:
  39
  40     @code
  41     wxDropSource dragSource( this );
  42     dragSource.SetData( my_data );
  43     wxDragResult result = dragSource.DoDragDrop( true );
  44     @endcode
  45
  46 @li @b Dragging: The call to DoDragDrop() blocks the program until the user releases
  47     the mouse button (unless you override the wxDropSource::GiveFeedback function to
  48     do something special). When the mouse moves in a window of a program which understands
  49     the same 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
  53 @li <b>Processing the result</b>: DoDragDrop() returns an @e effect code which
  54     is one of the values of @c wxDragResult enum (explained in wxDropTarget page):
  55
  56     @code
  57     switch (result)
  58     {
  59         case wxDragCopy:
  60             // copy the data
  61             break;
  62         case wxDragMove:
  63             // move the data
  64             break;
  65         default:
  66             // do nothing
  67             break;
  68     }
  69     @endcode
  70
  71
  72 To be a @e drop target, i.e. to receive the data dropped by the user you should
  73 follow the instructions below:
  74
  75 @li @b Initialization: For a window to be a drop target, it needs to have
  76     an associated wxDropTarget object. Normally, you will call wxWindow::SetDropTarget
  77     during window creation associating your drop target with it. You must derive a class
  78     from wxDropTarget and override its pure virtual methods. Alternatively, you may
  79     derive from wxTextDropTarget or wxFileDropTarget and override their OnDropText()
  80     or OnDropFiles() method.
  81
  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
  89 @li <b>The end</b>: After processing the data, DoDragDrop() returns either
  90     wxDragCopy or wxDragMove depending on the state of the keys Ctrl, Shift
  91     and Alt at the moment of the drop. There is currently no way for the drop
  92     target to change this return code.
  93
  94 */
  95