36c9828f70
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51911 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
81 lines
3.7 KiB
C
81 lines
3.7 KiB
C
/////////////////////////////////////////////////////////////////////////////
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// Name: dataobject
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// Purpose: topic overview
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// Author: wxWidgets team
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// RCS-ID: $Id$
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// Licence: wxWindows license
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/////////////////////////////////////////////////////////////////////////////
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/*!
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@page dataobject_overview wxDataObject overview
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Classes: #wxDataObject,
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#wxClipboard,
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#wxDataFormat,
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#wxDropSource,
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#wxDropTarget
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See also: @ref dnd_overview and @ref samplednd_overview
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This overview discusses data transfer through clipboard or drag and drop. In
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wxWidgets, these two ways to transfer data (either between different
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applications or inside one and the same) are very similar which allows to
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implement both of them using almost the same code - or, in other
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words, if you implement drag and drop support for your application, you get
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clipboard support for free and vice versa.
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At the heart of both clipboard and drag and drop operations lies the
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#wxDataObject class. The objects of this class (or, to
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be precise, classes derived from it) represent the data which is being carried
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by the mouse during drag and drop operation or copied to or pasted from the
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clipboard. wxDataObject is a "smart" piece of data because it knows which
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formats it supports (see GetFormatCount and GetAllFormats) and knows how to
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render itself in any of them (see GetDataHere). It can also receive its value
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from the outside in a format it supports if it implements the SetData method.
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Please see the documentation of this class for more details.
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Both clipboard and drag and drop operations have two sides: the source and
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target, the data provider and the data receiver. These which may be in the same
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application and even the same window when, for example, you drag some text from
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one position to another in a word processor. Let us describe what each of them
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should do.
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#The data provider (source) duties
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#The data receiver (target) duties
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@section wxdataobjectsource The data provider (source) duties
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The data provider is responsible for creating a
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#wxDataObject containing the data to be
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transferred. Then it should either pass it to the clipboard using
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#SetData function or to
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#wxDropSource and call
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#DoDragDrop function.
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The only (but important) difference is that the object for the clipboard
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transfer must always be created on the heap (i.e. using @c new) and it will
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be freed by the clipboard when it is no longer needed (indeed, it is not known
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in advance when, if ever, the data will be pasted from the clipboard). On the
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other hand, the object for drag and drop operation must only exist while
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#DoDragDrop executes and may be safely deleted
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afterwards and so can be created either on heap or on stack (i.e. as a local
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variable).
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Another small difference is that in the case of clipboard operation, the
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application usually knows in advance whether it copies or cuts (i.e. copies and
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deletes) data - in fact, this usually depends on which menu item the user
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chose. But for drag and drop it can only know it after
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#DoDragDrop returns (from its return value).
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@section wxdataobjecttarget The data receiver (target) duties
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To receive (paste in usual terminology) data from the clipboard, you should
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create a #wxDataObject derived class which supports the
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data formats you need and pass it as argument to
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wxClipboard::GetData. If it returns @false,
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no data in (any of) the supported format(s) is available. If it returns @true, the data has been successfully transferred to wxDataObject.
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For drag and drop case, the wxDropTarget::OnData
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virtual function will be called when a data object is dropped, from which the
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data itself may be requested by calling
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wxDropTarget::GetData method which fills
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the data object.
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*/
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