tkinter: using scrollbars on a canvas

Question

I'm trying to make a canvas scrollable. However, once I try to set up scrollbars to work with the canvas, tkinter seems to completely ignore the dimensions I initially set for my canvas. I've tried packing them all in a frame, setting the canvas to fill the frame and then setting the frame size, but that presents the same problem unless I set the frame to fill the window as well, which isn't what I want. Basically, I want a fixed-size canvas with scrollbars on it. My current code looks like this (in python 3.1):

from tkinter import *
root=Tk()
frame=Frame(root,width=300,height=300)
frame.grid(row=0,column=0)
canvas=Canvas(frame,bg='#FFFFFF',width=300,height=300,scrollregion=(0,0,500,500))
hbar=Scrollbar(canvas,orient=HORIZONTAL)
hbar.pack(side=BOTTOM,fill=X)
hbar.config(command=canvas.xview)
vbar=Scrollbar(canvas,orient=VERTICAL)
vbar.pack(side=RIGHT,fill=Y)
vbar.config(command=canvas.yview)
canvas.config(width=300,height=300)
canvas.config(xscrollcommand=hbar.set, yscrollcommand=vbar.set)
canvas.pack(side=LEFT,expand=True,fill=BOTH)

root.mainloop()

Answer 1

Your scrollbars need to have the Frame as a parent, not the Canvas:

from tkinter import *
root=Tk()
frame=Frame(root,width=300,height=300)
frame.pack(expand=True, fill=BOTH) #.grid(row=0,column=0)
canvas=Canvas(frame,bg='#FFFFFF',width=300,height=300,scrollregion=(0,0,500,500))
hbar=Scrollbar(frame,orient=HORIZONTAL)
hbar.pack(side=BOTTOM,fill=X)
hbar.config(command=canvas.xview)
vbar=Scrollbar(frame,orient=VERTICAL)
vbar.pack(side=RIGHT,fill=Y)
vbar.config(command=canvas.yview)
canvas.config(width=300,height=300)
canvas.config(xscrollcommand=hbar.set, yscrollcommand=vbar.set)
canvas.pack(side=LEFT,expand=True,fill=BOTH)

root.mainloop()

The reason why this works is due to how pack works. By default it will attempt to shrink (or grow) a container to exactly fit its children. Because the scrollbars are children of the canvas in the original example, the canvas shrinks to fit.

If you want the scrollbars to appear inside the canvas, the trick is to use an extra frame. Place the canvas and scrollbars in this inner frame, turn the borders off of the canvas and on for the frame. Set the background of the frame to be the same as the canvas and it will appear that the scrollbars are inside the canvas.