75 lines
3.4 KiB
TeX
75 lines
3.4 KiB
TeX
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\section{Drag-and-drop and clipboard 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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Samples: see the dnd sample.
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This overview describes wxWindows support for drag and drop and clipboard
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operations. Both of these topics are discussed here because, in fact, they're
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quite related. Drag and drop and clipboard are just too ways of passing the
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data around and so the code required to implement both types of the operations
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is almost the same.
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In any case, you work with some data which is represented by the
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\helpref{wxDataObject}{wxdataobject} class. It is capable to contain any kind
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data in one of any of predefined formats (see enum
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\helpref{StdFormatand}{stdformat}) and is smart enough to describe the format
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of data it contains. There is also a specialization of this class which stores
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only text - the only difference between
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\helpref{wxTextDataObject}{wxtextdataobject} and wxDataObject is that the
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first one is easily constructed from wxString.
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Also, for both kinds of operations, there is a sender which provides data and
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a receiver who gets it. The sender is responsible for constructing the
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wxDataObject and the receiver can query it and process the data it contains
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in any way he likes.
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In the case of a drag and drop operation, the sender is called a {\it drop
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source} while the receiver is a {\it dtop target}. There are several steps in
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the dragging process:
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\begin{itemize}\itemsep=0pt
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\item{preparation} First of all, the data object must be created and
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initilized with the data you wish to drag. For example:
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\begin{verbatim}
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wxTextDataObject data("This string will be dragged.");
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\end{verbatim}. Of course, the data object may contain arbitrary data of any
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type.
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\item{drag start} This happens when you call
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\helpref{DoDragDrop}{wxdropsourcedodragdrop} function. For this you must first
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construct a wxDropSource object and associate the data object from the
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previous step with it like this:
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\begin{verbatim}
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wxDropSource dragSource(data, this);
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// or also:
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wxDropSource dragSource(this);
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dragSource.SetData(data);
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\end{verbatim},
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\item{dragging} The call to DoDragDrop() blocks until the user release the
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mouse button (unless you override
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\helpref{GiveFeedback}{wxdropsourcegivefeedback} function to do something
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special). When the mouse moves in a window of a wxWindows program, the
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corresponding wxDropTarget methods are called (the data can be also dragged to
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any other program under Windows or to any program supporting the same protocol
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under X Windows).
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\item{drop} When the user releases the mouse over a window, wxWindows verifies
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if the wxDropTarget object associated (with
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\helpref{SetDropTarget}{setdroptarget}) with this window accepts the data. For
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this, \helpref{GetFormatCount}{wxdroptargetgetformatcount} and
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\helpref{GetFormat}{wxdroptargetgetformat} are used and if the format is
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supported (i.e. is one of returned by GetFormat()), then
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\helpref{OnDrop}{wxdroptargetondrop} is called. Otherwise, wxDragNone is
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returned by DoDragDrop() and nothing happens.
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\item{the end} Finally, the receiver processes the data (e.g. pastes the text
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in it's window). DoDragDrop() returns either wxDragCopy or wxDragMove
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depending on the state of the keys (<Ctrl>, <Shift> and <Alt>) at the moment
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of drop.
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\end{itemize}
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