docs/latex/wx/tdnd.tex

   1 \section{Drag-and-drop and clipboard 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'n'Drop in wxWindows.
  12
  13 This overview describes wxWindows support for drag and drop and clipboard
  14 operations. Both of these topics are discussed here because, in fact, they're
  15 quite related. Drag and drop and clipboard are just two ways of passing the
  16 data around and so the code required to implement both types of the operations
  17 is almost the same.
  18
  19 Both operations involve passing some data from one program to another,
  20 although the data can be received in the same program as the source. In the case
  21 of clipboard transfer, the data is first placed on the clipboard and then
  22 pasted into the destination program, while for a drag-and-drop operation the
  23 data object is not stored anywhere but is created when the user starts
  24 dragging and is destroyed as soon as he ends it, whether the operation was
  25 ended successfully or cancelled.
  26
  27 To be a {\it drag source}, i.e. to provide the data which may be dragged by
  28 user elsewhere, you should implement the following steps:
  29
  30 \begin{itemize}\itemsep=0pt
  31 \item {\bf Preparation:} First of all, the data object must be created and
  32 initialized with the data you wish to drag. For example:
  33
  34 \begin{verbatim}
  35         wxDataObject *my_data = new wxTextDataObject data("This string will be dragged.");
  36 \end{verbatim}
  37 \item{\bf Drag start:} To start dragging process (typically in response to a
  38 mouse click) you must call \helpref{DoDragDrop}{wxdropsourcedodragdrop} function
  39 of wxDropSource object which should be constructed like this:
  40
  41 \begin{verbatim}
  42         wxDropSource dragSource( this );
  43         dragSource.SetData( my_data );
  44 \end{verbatim}
  45 \item {\bf Dragging:} The call to DoDragDrop() blocks until the user release the
  46 mouse button (unless you override \helpref{GiveFeedback}{wxdropsourcegivefeedback} function
  47 to do something special). When the mouse moves in a window of a program which understands the
  48 same drag-and-drop protocol (any program under Windows or any program supporting the
  49 XDnD protocol under X Windows), the corresponding \helpref{wxDropTarget}{wxdroptarget} methods
  50 are called - see below.
  51 \item {\bf Processing the result:} DoDragDrop() returns an {\it effect code} which
  52 is one of the values of \helpref{wxDragResult}{wxdropsource} enum. Codes
  53 of wxDragError, wxDragNone and wxDragCancel have the obvious meaning and mean
  54 that there is nothing to do on the sending end (except of possibly logging the
  55 error in the first case). wxDragCopy means that the data has been successfully
  56 copied and doesn't require any specific actions neither. But wxDragMove is
  57 special because it means that the data must be deleted from where it was
  58 copied. If it doesn't make sense (dragging selected text from a read-only
  59 file) you should pass FALSE as parameter to DoDragDrop() in the previous step.
  60 \end{itemize}
  61
  62 To be a {\it drop target}, i.e. to receive the data dropped by user you should
  63 follow the instructions below:
  64
  65 \begin{itemize}\itemsep=0pt
  66 \item {\bf Initialization:} For a window to be drop target, it needs to have
  67 an associated \helpref{wxDropTarget}{wxdroptarget} object. Normally, you will
  68 call \helpref{wxWindow::SetDropTarget}{wxwindowsetdroptarget} during window
  69 creation associating you drop target with it. You must derive a class from
  70 wxDropTarget and override its pure virtual methods. Alternatively, you may
  71 derive from \helpref{wxTextDropTarget}{wxtextdroptarget} or
  72 \helpref{wxFileDropTarget}{wxfiledroptarget} and override their OnDropText()
  73 or OnDropFiles() method.
  74 \item {\bf Drop:} When the user releases the mouse over a window, wxWindows
  75 queries the associated wxDropTarget object if it accepts the data. For this,
  76 a \helpref{wxDataObject}{wxdataobject} must be associated with the drop target
  77 and this data object will be responsible for the format negotiation between
  78 the drag source and the drop target. If all goes well, then \helpref{OnData}{wxdroptargetondata}
  79 will get called and the wxDataObject belonging to the drop target can get
  80 filled with data.
  81 \item {\bf The end:} After processing the data, DoDragDrop() returns either
  82 wxDragCopy or wxDragMove depending on the state of the keys (<Ctrl>, <Shift>
  83 and <Alt>) at the moment of drop. There is currently no way for the drop
  84 target to change this return code.
  85 \end{itemize}
  86