How do I bind <MouseWheel> to scrollbar?

[James Stroud]

Nicholas Shewmaker wrote:
> (I apologize if this posts twice. My AVG is being fussy.)
> 
>  From what I've read, MouseWheel is a very tricky event.  I have 
> replaced my Python tcl84.dll and tk84.dll files with those in the 
> ActiveTcl distribution to fix the crashes caused by the event.  Then, I 
> managed to see that my test script (see code below) was registering the 
> event by printing the delta value (+/- 120).
> 
> -----------------
> from Tkinter import *
> 
> def reportScroll(event):
>     print "scrolled", event.delta, event
> 
> root = Tk()
> 
> myListbox = Listbox(root, selectmode=SINGLE, height=10, width=20)
> for x in range(30):
>     myListbox.insert(END, x)
> myListbox.pack(side=LEFT, expand=YES, fill=BOTH)
> 
> myScrollbar = Scrollbar(root, command=myListbox.yview)
> myScrollbar.bind('<MouseWheel>', reportScroll)
> myScrollbar.focus_set()
> myScrollbar.pack(side=RIGHT, fill=Y)
> 
> myListbox.config(yscrollcommand=myScrollbar.set)
> 
> root.mainloop()
> -----------------
> 
> The scrollbar and listbox are tied together, but moving the wheelmouse 
> does nothing.  I realize the code above doesn't give the event any real 
> duties, but I'm not really sure how to make that leap.  How and to what 
> do I bind <WheelMouse> so that it will affect the listbox and the 
> scrollbar?

I don't think <MouseWheel> is a real event in Tkinter. Try binding to 
<Button-4> and <Button-5>:

myListbox.bind('<Button-4>', lambda e, s=self:  \
                            s._scroll(SCROLL, -1, UNITS))
myListbox.bind('<Button-5>', lambda e, s=self:  \
                             s._scroll(SCROLL, 1, UNITS))

These have worked for me on Linux and OS X. They probably work under 
windows if you are lucky.

You will need to bind the scrollbar separately if you want it to respond 
to the mousewheel.

See also:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52266

(and the discussion that follows).

James