954b8ae603
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@1698 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
89 lines
4.1 KiB
TeX
89 lines
4.1 KiB
TeX
\section{\class{wxDataObject}}\label{wxdataobject}
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A wxDataObject represents data that can be copied to or from the clipboard, or
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dragged and dropped.
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There are several predefined data object classes, such as \helpref{wxFileDataObject}{wxfiledataobject},
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\helpref{wxTextDataObject}{wxtextdataobject}, and \helpref{wxBitmapDataObject}{wxbitmapdataobject} which
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can be used without change or can be altered (by deriving a new class from them) in order to deliver
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data and data size on-demand. There is no need to ever use wxDataObject itself or derive directly from it.
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You may also derive your own data object classes from \helpref{wxPrivateDataObject}{wxprivatedataobject}
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for user-defined types. The format of user-defined data is given as mime-type string literal,
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such as "application/word" or "image/png". These strings are used as they are under Unix (so
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far only GTK) to identify a format and are translated into their Windows equivalent under
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Win32 (using the OLE IDataObject for data exchange to and from the clipboard and for Drag'n'Drop).
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Note that the format string translation under Windows is not yet finnished.
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As mentioned above, data may be placed into the \helpref{wxClipboard}{wxclipboard}
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or a \helpref{wxDropSource}{wxdropsource} instance either directly or on-demand.
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As long as only one format is offerred, putting data directly into the clipboard may
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be sufficient. But imagine that you paste a large piece of text to the clipboard and
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offer it in "text/plain", "text/rtf", "text/html", "application/word" and your own
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format for internal use - here offering data on-demand is required to minimize memory
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consumption. This would generally get implemented using a central object that
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contains clipboard information in the format with the maximum of information. Note
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that neither the GTK data transfer mechanisms for the clipboard and Drag'n'Drop
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nor the OLE data transfer copies any data until another application actually
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requests the data. This is in contrast to the "feel" offered to the user of a
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program who would normally think that the data resides in the clipboard after
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having pressed "Copy" - in reality it is only declared to be available.
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Let's assume that you have written an HTML editor and want it to paste contents
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in the formats "text/plain" and "text/html" to the clipboard. For offering
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data on-demand in "text/plain" you would derive your class from \helpref{wxTextDataObject}{wxtextdataobject}
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and for offering data on-demand in "text/html" you would derive your own class from
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\helpref{wxPrivateDataObject}{wxprivatedataobject} and set its ID string
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identifying the format to "text/html" using \helpref{wxPrivateDataObject::SetId}{wxprivatedataobjectsetid}.
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In your two derived classed you'd then have a pointer or reference to the central
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data container and you'd override the methods returning the size of the
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available data and the WriteData() methods in both classes.
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\wxheading{Derived from}
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\helpref{wxObject}{wxobject}
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\wxheading{Include files}
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<wx/dataobj.h>
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\wxheading{See also}
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\helpref{wxFileDataObject}{wxfiledataobject},
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\helpref{wxTextDataObject}{wxtextdataobject},
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\helpref{wxBitmapDataObject}{wxbitmapdataobject},
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\helpref{wxPrivateDataObject}{wxprivatedataobject},
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\helpref{Drag and drop overview}{wxdndoverview}, \helpref{wxDropTarget}{wxdroptarget},
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\helpref{wxDropSource}{wxdropsource},
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\helpref{wxTextDropTarget}{wxtextdroptarget}, \helpref{wxFileDropTarget}{wxfiledroptarget}
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\latexignore{\rtfignore{\wxheading{Members}}}
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\membersection{wxDataObject::wxDataObject}\label{wxdataobjectwxdataobject}
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\func{}{wxDataObject}{\void}
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Constructor.
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\membersection{wxDataObject::\destruct{wxDataObject}}\label{wxdataobjectdtor}
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\func{}{\destruct{wxDataObject}}{\void}
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Destructor.
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\membersection{wxDataObject::WriteData}\label{wxdataobjectwritedata}
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\constfunc{virtual void}{WriteData}{\param{void}{*dest} }
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Write the data owned by this class to {\it dest}. This method is a pure
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virtual function and must be overridden.
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\membersection{wxDataObject::GetSize}\label{wxdataobjectgetdatasize}
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\constfunc{virtual size\_t}{GetSize}{\void}
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Returns the data size. This method is a pure
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virtual function and must be overridden.
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