80793cda3e
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@19209 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
85 lines
3.9 KiB
TeX
85 lines
3.9 KiB
TeX
\section{Drag and drop overview}\label{wxdndoverview}
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Classes: \helpref{wxDataObject}{wxdataobject},
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\helpref{wxTextDataObject}{wxtextdataobject},
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\helpref{wxDropSource}{wxdropsource},
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\helpref{wxDropTarget}{wxdroptarget},
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\helpref{wxTextDropTarget}{wxtextdroptarget},
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\helpref{wxFileDropTarget}{wxfiledroptarget}
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Note that wxUSE\_DRAG\_AND\_DROP must be defined in setup.h in order
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to use drag and drop in wxWindows.
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See also: \helpref{wxDataObject overview}{wxdataobjectoverview} and \helpref{DnD sample}{samplednd}
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It may be noted that data transfer to and from the clipboard is quite
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similar to data transfer with drag and drop and the code to implement
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these two types is almost the same. In particular, both data transfer
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mechanisms store data in some kind of \helpref{wxDataObject}{wxdataobject}
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and identify its format(s) using the \helpref{wxDataFormat}{wxdataformat}
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class.
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To be a {\it drag source}, i.e. to provide the data which may be dragged by
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the user elsewhere, you should implement the following steps:
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\begin{itemize}\itemsep=0pt
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\item {\bf Preparation:} First of all, a data object must be created and
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initialized with the data you wish to drag. For example:
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\begin{verbatim}
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wxTextDataObject my_data("This text will be dragged.");
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\end{verbatim}
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\item{\bf Drag start:} To start the dragging process (typically in response to a
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mouse click) you must call \helpref{wxDropSource::DoDragDrop}{wxdropsourcedodragdrop}
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like this:
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\begin{verbatim}
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wxDropSource dragSource( this );
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dragSource.SetData( my_data );
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wxDragResult result = dragSource.DoDragDrop( TRUE );
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\end{verbatim}
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\item {\bf Dragging:} The call to DoDragDrop() blocks the program until the user releases the
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mouse button (unless you override the \helpref{GiveFeedback}{wxdropsourcegivefeedback} function
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to do something special). When the mouse moves in a window of a program which understands the
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same drag-and-drop protocol (any program under Windows or any program supporting the
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XDnD protocol under X Windows), the corresponding \helpref{wxDropTarget}{wxdroptarget} methods
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are called - see below.
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\item {\bf Processing the result:} DoDragDrop() returns an {\it effect code} which
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is one of the values of {\tt wxDragResult} enum (explained \helpref{here}{wxdroptarget}):
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\begin{verbatim}
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switch (result)
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{
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case wxDragCopy: /* copy the data */ break;
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case wxDragMove: /* move the data */ break;
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default: /* do nothing */ break;
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}
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\end{verbatim}
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\end{itemize}
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To be a {\it drop target}, i.e. to receive the data dropped by the user you should
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follow the instructions below:
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\begin{itemize}\itemsep=0pt
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\item {\bf Initialization:} For a window to be a drop target, it needs to have
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an associated \helpref{wxDropTarget}{wxdroptarget} object. Normally, you will
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call \helpref{wxWindow::SetDropTarget}{wxwindowsetdroptarget} during window
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creation associating your drop target with it. You must derive a class from
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wxDropTarget and override its pure virtual methods. Alternatively, you may
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derive from \helpref{wxTextDropTarget}{wxtextdroptarget} or
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\helpref{wxFileDropTarget}{wxfiledroptarget} and override their OnDropText()
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or OnDropFiles() method.
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\item {\bf Drop:} When the user releases the mouse over a window, wxWindows
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asks the associated wxDropTarget object if it accepts the data. For this,
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a \helpref{wxDataObject}{wxdataobject} must be associated with the drop target
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and this data object will be responsible for the format negotiation between
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the drag source and the drop target. If all goes well, then \helpref{OnData}{wxdroptargetondata}
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will get called and the wxDataObject belonging to the drop target can get
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filled with data.
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\item {\bf The end:} After processing the data, DoDragDrop() returns either
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wxDragCopy or wxDragMove depending on the state of the keys <Ctrl>, <Shift>
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and <Alt> at the moment of the drop. There is currently no way for the drop
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target to change this return code.
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\end{itemize}
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