Python Cookbook 2Nd Edition Jun 1002005 [Electronic resources] نسخه متنی

Recipe 11.4. Adding Drag and Drop Reordering to a Tkinter Listbox

Credit: John Fouhy

Problem

You want to use a Tkinter
Listbox widget, but you want to give the user the
additional capability of reordering the entries by drag-and-drop.

Solution

We just need to code the relevant functionality and bind it to the
Tkinter event corresponding to the
"drag" mouse gesture:

import Tkinter
class DDList(Tkinter.Listbox):
"" A Tkinter listbox with drag'n'drop reordering of entries. ""
def _ _init_ _(self, master, **kw):
kw['selectmode'] = Tkinter.SINGLE
Tkinter.Listbox._ _init_ _(self, master, kw)
self.bind('<Button-1>', self.setCurrent)
self.bind('<B1-Motion>', self.shiftSelection)
self.curIndex = None
def setCurrent(self, event):
self.curIndex = self.nearest(event.y)
def shiftSelection(self, event):
i = self.nearest(event.y)
if i < self.curIndex:
x = self.get(i)
self.delete(i)
self.insert(i+1, x)
self.curIndex = i
elif i > self.curIndex:
x = self.get(i)
self.delete(i)
self.insert(i-1, x)
self.curIndex = i

Discussion

Here is an
example of use of this DDList class, presented, as
usual, with a guard of if _ _name_ _ ==
'_ _main_ _' so we can make it part of
the module containing the class and have it run when the module is
executed as a "main script":

if _ _name_ _ == '_ _main_ _':
tk = Tkinter.Tk( )
length = 10
dd = DDList(tk, height=length)
dd.pack( )
for i in xrange(length):
dd.insert(Tkinter.END, str(i))
def show( ):
''' show the current ordering every 2 seconds '''
for x in dd.get(0, Tkinter.END):
print x,
print
tk.after(2000, show)
tk.after(2000, show)
tk.mainloop( )

Allowing the user of a GUI program to drag the elements of a list
into new positions is often useful, and this recipe shows a fairly
simple way of adding this functionality to a Tkinter
Listbox widget.

This recipe's code tries to ensure that the
clicked-on element stays selected by deleting and inserting on either
side of it. Nevertheless, it is possible, by
moving the mouse quickly enough, to start dragging an unselected
element instead. While it doesn't cause any major
problems, it just looks a bit odd.

This recipe's code is partly based on a post by
Fredrik Lundh, http://mail.python.org/pipermail/python-list/1999-May/002501l.

See Also

Information about Tkinter can be obtained from a variety of sources,
such as Fredrik Lundh, An Introduction to
Tkinter (PythonWare: http://www.pythonware.com/library), New
Mexico Tech's Tkinter
Reference (http://www.nmt.edu/tcc/help/lang/python/docsl),
Python in a Nutshell, and various other books.