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ReStructuredText
50 lines
2.9 KiB
ReStructuredText
.. include:: headings.inc
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.. _dataobject overview:
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=================================================
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|phoenix_title| **DataObject Overview**
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=================================================
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This overview discusses data transfer through clipboard or drag and drop. In wxPython, these two ways to transfer
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data (either between different applications or inside one and the same) are very similar which allows to implement
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both of them using almost the same code - or, in other words, if you implement drag and drop support for your
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application, you get clipboard support for free and vice versa.
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At the heart of both clipboard and drag and drop operations lies the :class:`DataObject` class. The objects of this
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class (or, to be precise, classes 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. :class:`DataObject` is a "smart" piece of data
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because it knows which formats it supports (see `GetFormatCount` and `GetAllFormats`) and knows how to render itself
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in any of them (see `GetDataHere`). It can also receive its value from the outside in a format it supports if it
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implements the `SetData` method. 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 target, the data provider and the data
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receiver. These which may be in the same application and even the same window when, for example, you drag some text
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from one position to another in a word processor. Let us describe what each of them should do.
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The data provider (source) duties
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---------------------------------
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The data provider is responsible for creating a :class:`DataObject` containing the data to be transferred. Then it
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should either pass it to the clipboard using :meth:`Clipboard.SetData` function or to :class:`DropSource` and call
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:meth:`DropSource.DoDragDrop` function.
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A small difference is that in the case of clipboard operation, the application usually knows in advance whether it
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copies or cuts (i.e. copies and deletes) data - in fact, this usually depends on which menu item the user chose.
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But for drag and drop it can only know it after :meth:`DropSource.DoDragDrop` returns (from its return value).
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The data receiver (target) duties
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---------------------------------
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To receive (paste in usual terminology) data from the clipboard, you should create a :class:`DataObject` derived
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class which supports the data formats you need and pass it as argument to :meth:`Clipboard.GetData`. If it returns
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``False``, no data in (any of) the supported format(s) is available. If it returns ``True``, the data has been
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successfully transferred to :class:`DataObject`.
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For drag and drop case, the :meth:`DropTarget.OnData` virtual function will be called when a data object is dropped,
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from which the data itself may be requested by calling :meth:`DropTarget.GetData` method which fills the data object.
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