docs/doxygen/overviews/dnd.h

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