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.. include:: headings.inc
.. _drag and drop overview:
===========================================
|phoenix_title| **Drag and Drop Overview**
===========================================
It may be noted that data transfer to and from the clipboard is quite
similar to data transfer with drag and drop and the code to implement
these two types is almost the same. In particular, both data transfer
mechanisms store data in some kind of :ref:`wx.DataObject` and identify
its format(s) using the :ref:`wx.DataFormat` class.
To be a `drag` source, i.e. to provide the data which may be dragged
by the user elsewhere, you should implement the following steps:
- **Preparation**: First of all, a data object must be created and
initialized with the data you wish to drag. For example::
my_data = wx.TextDataObject("This text will be dragged.")
- **Drag start**: To start the dragging process (typically in response
to a mouse click) you must call :meth:`wx.DropSource.DoDragDrop` like
this::
dragSource = wx.DropSource(self)
dragSource.SetData(my_data)
result = dragSource.DoDragDrop(True)
- **Dragging**: The call to `DoDragDrop()` blocks the program until
the user releases the mouse button (unless you override the
:meth:`wx.DropSource.GiveFeedback` function to do something
special). When the mouse moves in a window of a program which
understands the same drag-and-drop protocol (any program under
Windows or any program supporting the XDnD protocol under X
Windows), the corresponding :ref:`wx.DropTarget` methods are called -
see below.
- **Processing the result**: `DoDragDrop()` returns an effect code
which is one of the values of :ref:`wx.DragResult`::
if result == wx.DragCopy:
# Copy the data
CopyMyData()
elif result == wx.DragMove:
# Move the data
MoveMyData()
else:
# Default, do nothing
pass
To be a `drop` target, i.e. to receive the data dropped by the user
you should follow the instructions below:
- **Initialization**: For a window to be a drop target, it needs to
have an associated :ref:`wx.DropTarget` object. Normally, you will
call :meth:`wx.Window.SetDropTarget` during window creation
associating your drop target with it. You must derive a class from
:ref:`wx.DropTarget` and override its pure virtual
methods. Alternatively, you may derive from :ref:`wx.TextDropTarget`
or :ref:`wx.FileDropTarget` and override their `OnDropText()` or
`OnDropFiles()` method.
- **Drop**: When the user releases the mouse over a window, wxPython
asks the associated :ref:`wx.DropTarget` object if it accepts the
data. For this, a :ref:`wx.DataObject` must be associated with the
drop target and this data object will be responsible for the format
negotiation between the drag source and the drop target. If all goes
well, then :meth:`wx.DropTarget.OnData` will get called and the
:ref:`wx.DataObject` belonging to the drop target can get filled
with data.
- **The end**: After processing the data, `DoDragDrop()` returns
either ``wx.DragCopy`` or ``wx.DragMove`` depending on the state of
the keys ``Ctrl``, ``Shift`` and ``Alt`` at the moment of the
drop. There is currently no way for the drop target to change this
return code.
|
