-\section{Drag-and-drop and clipboard overview}\label{wxdndoverview}
+\section{Drag and drop overview}\label{wxdndoverview}
Classes: \helpref{wxDataObject}{wxdataobject},
\helpref{wxTextDataObject}{wxtextdataobject},
\helpref{wxFileDropTarget}{wxfiledroptarget}
Note that wxUSE\_DRAG\_AND\_DROP must be defined in setup.h in order
-to use Drag'n'Drop in wxWindows.
+to use drag and drop in wxWindows.
-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.
+See also: \helpref{wxDataObject overview}{wxdataobjectoverview} and \helpref{DnD sample}{samplednd}
-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}
- wxDataObject *my_data = new wxTextDataObject data("This string will be dragged.");
+ wxTextDataObject my_data("This text will be dragged.");
\end{verbatim}
-\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( 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 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,
+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