77 lines
3.6 KiB
C
77 lines
3.6 KiB
C
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/////////////////////////////////////////////////////////////////////////////
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// Name: dataobject.h
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// Purpose: topic overview
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// Author: wxWidgets team
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// Licence: wxWindows licence
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/////////////////////////////////////////////////////////////////////////////
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/**
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@page overview_dataobject wxDataObject Overview
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@tableofcontents
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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 words, if you
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implement drag and drop support for your application, you get clipboard support
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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 be precise, classes
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derived from it) represent the data which is being carried by the mouse during
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drag and drop operation or copied to or pasted from the clipboard. wxDataObject
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is a "smart" piece of data because it knows which formats it supports (see
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GetFormatCount and GetAllFormats) and knows how to render itself in any of them
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(see GetDataHere). It can also receive its value from the outside in a format
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it supports if it implements the SetData method. Please see the documentation
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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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@see @ref overview_dnd, @ref group_class_dnd, @ref page_samples_dnd
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@section overview_dataobject_source The Data Provider (Source)
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The data provider is responsible for creating a wxDataObject containing the
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data to be transferred. Then it should either pass it to the clipboard using
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wxClipboard::SetData function or to wxDropSource and call
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wxDropSource::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 be
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freed by the clipboard when it is no longer needed (indeed, it is not known in
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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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wxDropSource::DoDragDrop executes and may be safely deleted afterwards and so
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can be created either on heap or on stack (i.e. as a local 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 wxDropSource::DoDragDrop
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returns (from its return value).
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@section overview_dataobject_target The Data Receiver (Target)
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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 data formats you need
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and pass it as argument to 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,
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the data has been successfully transferred to wxDataObject.
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For drag and drop case, the wxDropTarget::OnData virtual function will be
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called when a data object is dropped, from which the data itself may be
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requested by calling wxDropTarget::GetData method which fills the data object.
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*/
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