docs/latex/wx/tdnd.tex

   1 \section{Drag and drop overview}\label{wxdndoverview}
   2
   3 Classes: \helpref{wxDataObject}{wxdataobject},
   4 \helpref{wxTextDataObject}{wxtextdataobject},
   5 \helpref{wxDropSource}{wxdropsource},
   6 \helpref{wxDropTarget}{wxdroptarget},
   7 \helpref{wxTextDropTarget}{wxtextdroptarget},
   8 \helpref{wxFileDropTarget}{wxfiledroptarget}
   9
  10 Note that wxUSE\_DRAG\_AND\_DROP must be defined in setup.h in order
  11 to use drag and drop in wxWidgets.
  12
  13 See also: \helpref{wxDataObject overview}{wxdataobjectoverview} and \helpref{DnD sample}{samplednd}
  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 \helpref{wxDataObject}{wxdataobject}
  19 and identify its format(s) using the \helpref{wxDataFormat}{wxdataformat}
  20 class.
  21
  22 To be a {\it drag source}, i.e. to provide the data which may be dragged by
  23 the user elsewhere, you should implement the following steps:
  24
  25 \begin{itemize}\itemsep=0pt
  26 \item {\bf Preparation:} First of all, a data object must be created and
  27 initialized with the data you wish to drag. For example:
  28
  29 \begin{verbatim}
  30         wxTextDataObject my_data("This text will be dragged.");
  31 \end{verbatim}
  32 \item{\bf Drag start:} To start the dragging process (typically in response to a
  33 mouse click) you must call \helpref{wxDropSource::DoDragDrop}{wxdropsourcedodragdrop}
  34 like this:
  35
  36 \begin{verbatim}
  37         wxDropSource dragSource( this );
  38         dragSource.SetData( my_data );
  39         wxDragResult result = dragSource.DoDragDrop( TRUE );
  40 \end{verbatim}
  41 \item {\bf Dragging:} The call to DoDragDrop() blocks the program until the user releases the
  42 mouse button (unless you override the \helpref{GiveFeedback}{wxdropsourcegivefeedback} function
  43 to do something special). When the mouse moves in a window of a program which understands the
  44 same drag-and-drop protocol (any program under Windows or any program supporting the
  45 XDnD protocol under X Windows), the corresponding \helpref{wxDropTarget}{wxdroptarget} methods
  46 are called - see below.
  47 \item {\bf Processing the result:} DoDragDrop() returns an {\it effect code} which
  48 is one of the values of {\tt wxDragResult} enum (explained \helpref{here}{wxdroptarget}):
  49
  50 \begin{verbatim}
  51         switch (result)
  52         {
  53             case wxDragCopy: /* copy the data */ break;
  54             case wxDragMove: /* move the data */ break;
  55             default:         /* do nothing */ break;
  56         }
  57 \end{verbatim}%
  58 \end{itemize}
  59
  60 To be a {\it drop target}, i.e. to receive the data dropped by the user you should
  61 follow the instructions below:
  62
  63 \begin{itemize}\itemsep=0pt
  64 \item {\bf Initialization:} For a window to be a drop target, it needs to have
  65 an associated \helpref{wxDropTarget}{wxdroptarget} object. Normally, you will
  66 call \helpref{wxWindow::SetDropTarget}{wxwindowsetdroptarget} during window
  67 creation associating your drop target with it. You must derive a class from
  68 wxDropTarget and override its pure virtual methods. Alternatively, you may
  69 derive from \helpref{wxTextDropTarget}{wxtextdroptarget} or
  70 \helpref{wxFileDropTarget}{wxfiledroptarget} and override their OnDropText()
  71 or OnDropFiles() method.
  72 \item {\bf Drop:} When the user releases the mouse over a window, wxWidgets
  73 asks the associated wxDropTarget object if it accepts the data. For this,
  74 a \helpref{wxDataObject}{wxdataobject} must be associated with the drop target
  75 and this data object will be responsible for the format negotiation between
  76 the drag source and the drop target. If all goes well, then \helpref{OnData}{wxdroptargetondata}
  77 will get called and the wxDataObject belonging to the drop target can get
  78 filled with data.
  79 \item {\bf The end:} After processing the data, DoDragDrop() returns either
  80 wxDragCopy or wxDragMove depending on the state of the keys <Ctrl>, <Shift>
  81 and <Alt> at the moment of the drop. There is currently no way for the drop
  82 target to change this return code.
  83 \end{itemize}
  84