-\section{Drag-and-drop and clipboard overview}\label{wxdndoverview}
+\section{Drag and drop overview}\label{wxdndoverview}
Classes: \helpref{wxDataObject}{wxdataobject},
\helpref{wxTextDataObject}{wxtextdataobject},
\helpref{wxTextDropTarget}{wxtextdroptarget},
\helpref{wxFileDropTarget}{wxfiledroptarget}
-Samples: see the dnd sample.
+Note that wxUSE\_DRAG\_AND\_DROP must be defined in setup.h in order
+to use drag and drop in wxWindows.
-Headers: <wx/dataobj.h>, <wx/dropsrc.h and <wx/droptgt.h> or <wx/dnd.h>
-(note that wxUSE\_DRAG\_AND\_DROP must be defined in setup.h)
+See also: \helpref{wxDataObject overview}{wxdataobjectoverview} and \helpref{DnD sample}{samplednd}
-This overview describes wxWindows support for drag and drop and clipboard
-operations. Both of these topics are discussed here because, in fact, they're
-quite related. Drag and drop and clipboard are just two ways of passing the
-data around and so the code required to implement both types of the operations
-is almost the same.
-
-Both operations involve passing some data from one program to another,
-although the data can be received in the same program as the source. In the case
-of clipboard transfer, the data is first placed on the clipboard and then
-pasted into the destination program, while for a drag-and-drop operation the
-data object is not stored anywhere but is created when the user starts
-dragging and is destroyed as soon as he ends it, whether the operation was
-ended successfully or cancelled.
+It may be noted that data transfer to and from the clipboard is quite
+similar to data transfer with drag and drop and the code to implement
+these two types is almost the same. In particular, both data transfer
+mechanisms store data in some kind of \helpref{wxDataObject}{wxdataobject}
+and identify its format(s) using the \helpref{wxDataFormat}{wxdataformat}
+class.
To be a {\it drag source}, i.e. to provide the data which may be dragged by
-user elsewhere, you should implement the following steps:
+the user elsewhere, you should implement the following steps:
\begin{itemize}\itemsep=0pt
-\item {\bf Preparation:} First of all, the data object must be created and
+\item {\bf Preparation:} First of all, a data object must be created and
initialized with the data you wish to drag. For example:
\begin{verbatim}
- wxTextDataObject data("This string will be dragged.");
+ wxTextDataObject my_data("This text will be dragged.");
\end{verbatim}
-
-Of course, the data object may contain arbitrary data of any type, but for
-this you should derive your own class from \helpref{wxDataObject}{wxdataobject} overriding all of its pure virtual
-functions.
-
-\item{\bf Drag start:} To start dragging process (typically in response to a
-mouse click) you must call \helpref{DoDragDrop}{wxdropsourcedodragdrop} function
-of wxDropSource object which should be constructed like this:
+\item{\bf Drag start:} To start the dragging process (typically in response to a
+mouse click) you must call \helpref{wxDropSource::DoDragDrop}{wxdropsourcedodragdrop}
+like this:
\begin{verbatim}
- wxDropSource dragSource(data, this);
-
- // or also:
-
- wxDropSource dragSource(this);
- dragSource.SetData(data);
+ wxDropSource dragSource( this );
+ dragSource.SetData( my_data );
+ wxDragResult result = dragSource.DoDragDrop( TRUE );
\end{verbatim}
-
-\item {\bf Dragging:} The call to DoDragDrop() blocks until the user release the
-mouse button (unless you override \helpref{GiveFeedback}{wxdropsourcegivefeedback} function
+\item {\bf Dragging:} The call to DoDragDrop() blocks the program until the user releases the
+mouse button (unless you override the \helpref{GiveFeedback}{wxdropsourcegivefeedback} function
to do something special). When the mouse moves in a window of a program which understands the
-same drag-and-drop protocol (any program under Windows or any program supporting XDnD protocol
-under X Windows), the corresponding \helpref{wxDropTarget}{wxdroptarget} methods
+same drag-and-drop protocol (any program under Windows or any program supporting the
+XDnD protocol under X Windows), the corresponding \helpref{wxDropTarget}{wxdroptarget} methods
are called - see below.
-
\item {\bf Processing the result:} DoDragDrop() returns an {\it effect code} which
-is one of the values of \helpref{wxDragResult}{wxdropsource} enum. Codes
-of wxDragError, wxDragNone and wxDragCancel have the obvious meaning and mean
-that there is nothing to do on the sending end (except of possibly logging the
-error in the first case). wxDragCopy means that the data has been successfully
-copied and doesn't require any specific actions neither. But wxDragMove is
-special because it means that the data must be deleted from where it was
-copied. If it doesn't make sense (dragging selected text from a read-only
-file) you should pass FALSE as parameter to DoDragDrop() in the previous step.
+is one of the values of {\tt wxDragResult} enum (explained \helpref{here}{wxdroptarget}):
+
+\begin{verbatim}
+ switch (result)
+ {
+ case wxDragCopy: /* copy the data */ break;
+ case wxDragMove: /* move the data */ break;
+ default: /* do nothing */ break;
+ }
+\end{verbatim}
\end{itemize}
-To be a {\it drop target}, i.e. to receive the data dropped by user you should
+To be a {\it drop target}, i.e. to receive the data dropped by the user you should
follow the instructions below:
\begin{itemize}\itemsep=0pt
-\item {\bf Initialization:} For a window to be drop target, it needs to have
+\item {\bf Initialization:} For a window to be a drop target, it needs to have
an associated \helpref{wxDropTarget}{wxdroptarget} object. Normally, you will
call \helpref{wxWindow::SetDropTarget}{wxwindowsetdroptarget} during window
-creation associating you drop target with it. You must derive a class from
+creation associating your drop target with it. You must derive a class from
wxDropTarget and override its pure virtual methods. Alternatively, you may
derive from \helpref{wxTextDropTarget}{wxtextdroptarget} or
\helpref{wxFileDropTarget}{wxfiledroptarget} and override their OnDropText()
or OnDropFiles() method.
-
\item {\bf Drop:} When the user releases the mouse over a window, wxWindows
-queries the associated wxDropTarget object if it accepts the data. For
-this, \helpref{GetFormatCount}{wxdroptargetgetformatcount} and \helpref{GetFormat}{wxdroptargetgetformat} are
-used and if the format is
-supported (i.e. is one of returned by GetFormat()),
-then \helpref{OnDrop}{wxdroptargetondrop} is called.
-Otherwise, wxDragNone is returned by DoDragDrop() and
-nothing happens.
-
+asks the associated wxDropTarget object if it accepts the data. For this,
+a \helpref{wxDataObject}{wxdataobject} must be associated with the drop target
+and this data object will be responsible for the format negotiation between
+the drag source and the drop target. If all goes well, then \helpref{OnData}{wxdroptargetondata}
+will get called and the wxDataObject belonging to the drop target can get
+filled with data.
\item {\bf The end:} After processing the data, DoDragDrop() returns either
-wxDragCopy or wxDragMove depending on the state of the keys (<Ctrl>, <Shift>
-and <Alt>) at the moment of drop. There is currently no way for the drop
+wxDragCopy or wxDragMove depending on the state of the keys <Ctrl>, <Shift>
+and <Alt> at the moment of the drop. There is currently no way for the drop
target to change this return code.
\end{itemize}
projects / wxWidgets.git / blobdiff