docs/latex/wx/tdnd.tex

   1 \section{Drag-and-drop and clipboard overview}\label{wxdndoverview}
   2
   3 Classes: \helpref{wxDataObject}{wxdataobject}
   4
   5 % \helpref{wxTextDataObject}{wxtextdataobject}
   6 % \helpref{wxDropSource}{wxdropsource}
   7 % \helpref{wxDropTarget}{wxdroptarget}
   8 % \helpref{wxTextDropTarget}{wxtextdroptarget}
   9 % \helpref{wxFileDropTarget}{wxfiledroptarget}
  10
  11 Samples: see the dnd sample.
  12
  13 Headers: <wx/dataobj.h>, <wx/dropsrc.h and <wx/droptgt.h>>
  14 (note that wxUSE\_DRAG\_AND\_DROP must be defined in setup.h)
  15
  16 This overview describes wxWindows support for drag and drop and clipboard
  17 operations. Both of these topics are discussed here because, in fact, they're
  18 quite related. Drag and drop and clipboard are just too ways of passing the
  19 data around and so the code required to implement both types of the operations
  20 is almost the same.
  21
  22 Both operations involve passing some data from one program to another
  23 (although the data may be received in the same program as well). In the case
  24 of clipboard transfer, the data is first places on the clipboard and then
  25 pasted into the destination program while for a drag-and-drop operation the
  26 data object is not stored anywhere but is created when the user starts
  27 dragging and is destroyed as soon as he ends it (whether the operation was
  28 ended successfully or cancelled).
  29
  30 To be a {\it drag source}, i.e. to provide the data which may be dragged by
  31 user elsewhere you should implement the following steps:
  32
  33 \begin{itemize}\itemsep=0pt
  34 \item {\bf Preparation:} First of all, the data object must be created and
  35 initilized with the data you wish to drag. For example:
  36
  37 \begin{verbatim}
  38         wxTextDataObject data("This string will be dragged.");
  39 \end{verbatim}
  40
  41 Of course, the data object may contain arbitrary data of any type, but for
  42 this you should derive your own class from
  43 \helpref{wxDataObject}{wxdataobject} overriding all of its pure virtual
  44 functions.
  45
  46 \item{\bf Drag start:} To start dragging process (typically in response to a
  47 mouse click) you must call \helpref{DoDragDrop}{wxdropsourcedodragdrop}
  48 function of wxDropSource object which should be constructed like this:
  49
  50 \begin{verbatim}
  51         wxDropSource dragSource(data, this);
  52
  53         // or also:
  54
  55         wxDropSource dragSource(this);
  56         dragSource.SetData(data);
  57 \end{verbatim}
  58
  59 \item {\bf Dragging:} The call to DoDragDrop() blocks until the user release the
  60 mouse button (unless you override \helpref{GiveFeedback}{wxdropsourcegivefeedback} function
  61 to do something special). When the mouse moves in a window of a program which understands the
  62 same drag-and-drop protocol (any program under Windows or any program supporting XDnD protocol
  63 under X Windows), the corresponding \helpref{wxDropTarget}{wxdroptarget} methods
  64 are called - see below.
  65
  66 \item {\bf Processing the result:} DoDragDrop() returns an {\it effect code}
  67 which is one of the values of \helpref{wxDragResult}{wxdragresult} enum. Codes
  68 of wxDragError, wxDragNone and wxDragCancel have the obvious meaning and mean
  69 that there is nothing to do on the sending end (except of possibly logging the
  70 error in the first case). wxDragCopy means that the data has been successfully
  71 copied and doesn't require any specific actions neither. But wxDragMove is
  72 special because it means that the data must be deleted from where it was
  73 copied. If it doesn't make sense (dragging selected text from a read-only
  74 file) you should pass FALSE as parameter to DoDragDrop() in the previous step.
  75
  76 \end{itemize}
  77
  78
  79 To be a {\it drop target}, i.e. to receive the data dropped by user you should
  80 follow the instructions below:
  81
  82 \begin{itemize}\itemsep=0pt
  83 \item {\bf Initialization:} For a window to be drop target, it needs to have
  84 an associated \helpref{wxDropTarget}{wxdroptarget} object. Normally, you will
  85 call wxWindow::\helpref{SetDropTarget}{wxwindowsetdroptarget} during window
  86 creation associating you drop target with it. You must derive a class from
  87 wxDropTarget and override its pure virtual methods. Alternatively, you may
  88 derive from \helpref{wxTextDropTarget}{wxtextdroptarget} or
  89 \helpref{wxFileDropTarget}{wxfiledroptarget} and override their OnDropText()
  90 or OnDropFiles() method.
  91
  92 \item {\bf Drop:} When the user releases the mouse over a window, wxWindows
  93 queries the associated wxDropTarget object if it accepts the data. For
  94 this, \helpref{GetFormatCount}{wxdroptargetgetformatcount} and
  95 \helpref{GetFormat}{wxdroptargetgetformat} are used and if the format is
  96 supported (i.e. is one of returned by GetFormat()),
  97 then \helpref{OnDrop}{wxdroptargetondrop} is called.
  98 Otherwise, \helpref{wxDragNone}{stdformat} is returned by DoDragDrop() and
  99 nothing happens.
 100
 101 \item {\bf The end:} After processing the data, DoDragDrop() returns either
 102 wxDragCopy or wxDragMove depending on the state of the keys (<Ctrl>, <Shift>
 103 and <Alt>) at the moment of drop. There is currently no way for the drop
 104 target to change this return code.
 105
 106 \end{itemize}
 107