docs/latex/wx/tclipbrd.tex

   1 \section{wxDataObject overview}\label{wxdataobjectoverview}
   2
   3 Classes: \helpref{wxDataObject}{wxdataobject},
   4  \helpref{wxClipboard}{wxclipboard},
   5  \helpref{wxDataFormat}{wxdataformat},
   6  \helpref{wxDropSource}{wxdropsource},
   7  \helpref{wxDropTarget}{wxdroptarget}
   8
   9 This overview discusses data transfer through clipboard or drag and drop. In
  10 wxWindows, these two ways to transfer data (either between different
  11 applications or inside one and the same) are very similar which allows to
  12 implement both of them using almost the same code - or, in other
  13 words, if you implement drag and drop support for your application, you get
  14 clipboard support for free and vice versa.
  15
  16 At the heart of both clipboard and drag and drop operations lies the
  17 \helpref{wxDataObject}{wxdataobject} class. The objects of this class (or, to
  18 be precise, classes derived from it) represent the data which is being carried
  19 by the mouse during drag and drop operation or copied to or pasted from the
  20 clipboard. wxDataObject is a "smart" piece of data because it knows which
  21 formats it supports (see GetFormatCount and GetAllFormats) and knows how to
  22 render itself in any of them (see GetDataHere). It can also receive its value
  23 from the outside in a format it supports if it implements the SetData method.
  24 Please see the documentation of this class for more details.
  25
  26 Both clipboard and drag and drop operations have two sides: the source and
  27 target, the data provider and the data receiver. These which may be in the same
  28 application and even the same window when, for example, you drag some text from
  29 one position to another in a word processor. Let us describe what each of them
  30 should do.
  31
  32 \subsection{The data provider (source) duties}\label{wxdataobjectsource}
  33
  34 The data provider is responsible for creating a
  35 \helpref{wxDataObject}{wxdataobject} containing the data to be
  36 transfered. Then it should either pass it to the clipboard using
  37 \helpref{SetData}{wxclipboardsetdata} function or to
  38 \helpref{wxDropSource}{wxdropsource} and call
  39 \helpref{DoDragDrop}{wxdropsourcedodragdrop} function.
  40
  41 The only (but important) difference is that the object for the clipboard
  42 transfer must always be created on the heap (i.e. using {\tt new}) and it will
  43 be freed by the clipboard when it is no longer needed (indeed, it is not known
  44 in advance when, if ever, the data will be pasted from the clipboard). On the
  45 other hand, the object for drag and drop operation must only exist while
  46 \helpref{DoDragDrop}{wxdropsourcedodragdrop} executes and may be safely deleted
  47 afterwards and so can be created either on heap or on stack (i.e. as a local
  48 variable).
  49
  50 Another small difference is that in the case of clipboard operation, the
  51 application usually knows in advance whether it copies or cuts (i.e. copies and
  52 deletes) data - in fact, this usually depends on which menu item the user
  53 chose. But for drag and drop it can only know it after
  54 \helpref{DoDragDrop}{wxdropsourcedodragdrop} returns (from its return value).
  55
  56 \subsection{The data receiver (target) duties}\label{wxdataobjecttarget}
  57
  58 To receive (paste in usual terminology) data from the clipboard, you should
  59 create a \helpref{wxDataObject}{wxdataobject} derived class which supports the
  60 data formats you need and pass it as argument to
  61 \helpref{wxClipboard::GetData}{wxclipboardgetdata}. If it returns {\tt FALSE},
  62 no data in (any of) the supported format(s) is available. If it returns {\tt
  63 TRUE}, the data has been successfully transfered to wxDataObject.
  64
  65 For drag and drop case, the \helpref{wxDropTarget::OnData}{wxdroptargetondata}
  66 virtual function will be called when a data object is dropped, from which the
  67 data itself may be requested by calling
  68 \helpref{wxDropTarget::GetData}{wxdroptargetwxdroptarget} method which fills
  69 the data object.
  70