Based on Bryan Oakley's comment and a variety of his posts on SO, and several days of work on my part, here is a pretty complete answer to the question. This scrollbar is configurable and can be optionally hidden when not needed. I am a beginner and this can be improved, but it seems to work OK. I left my comments in, as well as Bryan Oakley's from an original post where he showed part of this code. This was not easy for me to do and the comments might help someone understand it better. I wrote this code a few weeks ago and it's working fine so far.
import tkinter as tk
'''
Much of this code was elucidated by Bryan Oakley on StackOverflow.com.
Without his explanations and examples, I would not have figured out how to
create a configurable Tkinter scrollbar. Any mistakes in this code are mine
of course.
I didn't add the little arrows at the ends of the trough.
'''
class Scrollbar(tk.Canvas):
'''
A scrollbar is gridded as a sibling of what it's scrolling.
'''
def __init__(self, parent, orient='vertical', hideable=False, **kwargs):
print('kwargs is', kwargs)
'''
kwargs is {
'width': 17,
'command': <bound method YView.yview of
<widgets.Text object .!canvas.!frame.!frame.!text>>}
https://stackoverflow.com/questions/15411107
You can use dict.pop:... delete an item in a dictionary only if the given key exists... not certain if key exists in the dictionary...
mydict.pop("key", None)
...if the second argument, None is not given, KeyError is raised if the key is not in the dictionary. Providing the second argument prevents the conditional exception... the second argument to .pop() is what it returns if the key is not found.
'''
self.command = kwargs.pop('command', None)
print('self.command is', self.command)
tk.Canvas.__init__(self, parent, **kwargs)
self.orient = orient
self.hideable = hideable
self.new_start_y = 0
self.new_start_x = 0
self.first_y = 0
self.first_x = 0
self.slidercolor = 'steelblue'
self.troughcolor = 'lightgray'
self.config(bg=self.troughcolor, bd=0, highlightthickness=0)
# coordinates are irrelevant; they will be recomputed
# in the 'set' method
self.create_rectangle(
0, 0, 1, 1,
fill=self.slidercolor,
width=2, # this is border width
outline='teal',
tags=('slider',))
self.bind('<ButtonPress-1>', self.move_on_click)
self.bind('<ButtonPress-1>', self.start_scroll, add='+')
self.bind('<B1-Motion>', self.move_on_scroll)
self.bind('<ButtonRelease-1>', self.end_scroll)
def set(self, lo, hi):
'''
For resizing & repositioning the slider. The hideable
scrollbar portion is by Fredrik Lundh, one of Tkinter's authors.
'''
lo = float(lo)
hi = float(hi)
if self.hideable is True:
if lo <= 0.0 and hi >= 1.0:
self.grid_remove()
return
else:
self.grid()
height = self.winfo_height()
width = self.winfo_width()
if self.orient == 'vertical':
x0 = 2
y0 = max(int(height * lo), 0)
x1 = width - 2
y1 = min(int(height * hi), height)
# This was the tricky part of making a horizontal scrollbar
# when I already knew how to make a vertical one.
# You can't just change all the "height" to "width"
# and "y" to "x". You also have to reverse what x0 etc
# are equal to, comparing code in if and elif. Till that was
# done, everything worked but the horizontal scrollbar's
# slider moved up & down.
elif self.orient == 'horizontal':
x0 = max(int(width * lo), 0)
y0 = 2
x1 = min(int(width * hi), width)
y1 = height
self.coords('slider', x0, y0, x1, y1)
self.x0 = x0
self.y0 = y0
self.x1 = x1
self.y1 = y1
def move_on_click(self, event):
if self.orient == 'vertical':
# don't scroll on click if mouse pointer is w/in slider
y = event.y / self.winfo_height()
if event.y < self.y0 or event.y > self.y1:
self.command('moveto', y)
# get starting position of a scrolling event
else:
self.first_y = event.y
elif self.orient == 'horizontal':
# do nothing if mouse pointer is w/in slider
x = event.x / self.winfo_width()
if event.x < self.x0 or event.x > self.x1:
self.command('moveto', x)
# get starting position of a scrolling event
else:
self.first_x = event.x
def start_scroll(self, event):
if self.orient == 'vertical':
self.last_y = event.y
self.y_move_on_click = int(event.y - self.coords('slider')[1])
elif self.orient == 'horizontal':
self.last_x = event.x
self.x_move_on_click = int(event.x - self.coords('slider')[0])
def end_scroll(self, event):
if self.orient == 'vertical':
self.new_start_y = event.y
elif self.orient == 'horizontal':
self.new_start_x = event.x
def move_on_scroll(self, event):
# Only scroll if the mouse moves a few pixels. This makes
# the click-in-trough work right even if the click smears
# a little. Otherwise, a perfectly motionless mouse click
# is the only way to get the trough click to work right.
# Setting jerkiness to 5 or more makes very sloppy trough
# clicking work, but then scrolling is not smooth. 3 is OK.
jerkiness = 3
if self.orient == 'vertical':
if abs(event.y - self.last_y) < jerkiness:
return
# scroll the scrolled widget in proportion to mouse motion
# compute whether scrolling up or down
delta = 1 if event.y > self.last_y else -1
# remember this location for the next time this is called
self.last_y = event.y
# do the scroll
self.command('scroll', delta, 'units')
# afix slider to mouse pointer
mouse_pos = event.y - self.first_y
if self.new_start_y != 0:
mouse_pos = event.y - self.y_move_on_click
self.command('moveto', mouse_pos/self.winfo_height())
elif self.orient == 'horizontal':
if abs(event.x - self.last_x) < jerkiness:
return
# scroll the scrolled widget in proportion to mouse motion
# compute whether scrolling left or right
delta = 1 if event.x > self.last_x else -1
# remember this location for the next time this is called
self.last_x = event.x
# do the scroll
self.command('scroll', delta, 'units')
# afix slider to mouse pointer
mouse_pos = event.x - self.first_x
if self.new_start_x != 0:
mouse_pos = event.x - self.x_move_on_click
self.command('moveto', mouse_pos/self.winfo_width())
def colorize(self):
print('colorize')
self.slidercolor = 'blue'
self.troughcolor = 'bisque'
self.config(bg=self.troughcolor)
if __name__ == '__main__':
def resize_scrollbar():
root.update_idletasks()
canvas.config(scrollregion=canvas.bbox('all'))
def resize_window():
root.update_idletasks()
page_x = content.winfo_reqwidth()
page_y = content.winfo_reqheight()
root.geometry('{}x{}'.format(page_x, page_y))
root = tk.Tk()
root.config(bg='yellow')
root.grid_columnconfigure(0, weight=1)
root.grid_rowconfigure(0, weight=1)
root.grid_rowconfigure(1, weight=0)
canvas = tk.Canvas(root, bg='tan')
canvas.grid(column=0, row=0, sticky='news')
content = tk.Frame(canvas)
content.grid_columnconfigure(0, weight=1)
content.grid_rowconfigure(0, weight=1)
ysb_canv = Scrollbar(root, width=24, hideable=True, command=canvas.yview)
xsb_canv = Scrollbar(root, height=24, hideable=True, command=canvas.xview, orient='horizontal')
canvas.config(yscrollcommand=ysb_canv.set, xscrollcommand=xsb_canv.set)
frame = tk.Frame(content)
frame.grid_columnconfigure(0, weight=0)
frame.grid_rowconfigure(0, weight=1)
text = tk.Text(frame, bd=0)
ysb_txt = Scrollbar(frame, width=17, command=text.yview)
text.config(yscrollcommand=ysb_txt.set)
space = tk.Frame(content, width=1200, height=500)
ysb_canv.grid(column=1, row=0, sticky='ns')
xsb_canv.grid(column=0, row=1, sticky='ew')
frame.grid(column=0, row=0, sticky='news')
text.grid(column=0, row=0)
ysb_txt.grid(column=1, row=0, sticky='ns')
space.grid(column=0, row=1)
with open(__file__, 'r') as f:
text.insert('end', f.read())
canvas.create_window(0, 0, anchor='nw', window=content)
resize_scrollbar()
resize_window()
root.mainloop()
