16. tk Scrollbar

See: https://docs.python.org/3/library/tkinter.html#tkinter.Scrollbar
See: https://www.geeksforgeeks.org/python-tkinter-scrollbar/

16.1. Usage

The tkinter.Scrollbar widget provides a horizontal or vertical scrollbar that allows the user to scroll the contents of another widget.
A scrollbar is commonly used with widgets such as Text, Canvas, Listbox and Treeview.
To create a scrollbar widget, the general syntax is
(assuming import via import tkinter as tk):
scrollbar_widget = tk.Scrollbar(parent, option=value)
parent is the window or frame object.
Options can be passed as parameters separated by commas.
A scrollbar must be linked to another widget using the widget's xview or yview method.

16.2. Using a Scrollbar

../_images/scrollbar.png 
import tkinter as tk

root = tk.Tk()
root.title("Scrollbar Example")

scrollbar = tk.Scrollbar(root)
scrollbar.pack(side="right", fill="y")

text = tk.Text(root, width=40, height=10,
               yscrollcommand=scrollbar.set)
text.pack(side="left", fill="both", expand=True)

scrollbar.config(command=text.yview)

for i in range(1, 21):
    text.insert("end", f"Line {i}\n")

root.mainloop()

Tasks

  1. Modify the program so that:

    • the Text widget displays 15 lines,

    • the scrollbar appears on the left of the window,

    • the Text widget is 30 characters wide.

    ../_images/scrollbar_question.png

Modify the code to produce the layout shown above.

import tkinter as tk

root = tk.Tk()
root.title("Scrollbar Question")

scrollbar = tk.Scrollbar(root)
scrollbar.pack(side="right", fill="y")

text = tk.Text(
    root,
    width=40,
    height=10,
    yscrollcommand=scrollbar.set
)
text.pack(side="left")

scrollbar.config(command=text.yview)

for i in range(1, 101):
    text.insert("end", f"Line {i}\n")

root.mainloop()

16.3. Methods

scrollbar_widget.activate(element=None)
Activates the specified scrollbar element.
If no element is supplied, returns the currently active element.
scrollbar_widget.delta(deltax, deltay)
Returns the amount the scrollbar should move for the specified mouse movement.
scrollbar_widget.fraction(x, y)
Returns the fractional position corresponding to the specified coordinates.
scrollbar_widget.get()
Returns the current position of the scrollbar as two fractions.
scrollbar_widget.identify(x, y)
Returns the name of the scrollbar element at the specified coordinates.
scrollbar_widget.set(first, last)
Updates the slider position.
This method is normally called automatically by the associated widget.

16.4. Parameter syntax

scrollbar_widget = tk.Scrollbar(parent, option=value)
parent is the window or frame object.
Options can be passed as parameters separated by commas.

Parameters:

activebackground
Syntax: scrollbar_widget = tk.Scrollbar(parent, activebackground="color")
Description: Sets the colour of the slider while it is active.
Default: SystemButtonFace
background
bg
Syntax: scrollbar_widget = tk.Scrollbar(parent, bg="color")
Description: Sets the background colour of the scrollbar.
Default: SystemButtonFace
borderwidth
bd
Syntax: scrollbar_widget = tk.Scrollbar(parent, borderwidth=value)
Description: Sets the border width.
Default: 2
command
Syntax: scrollbar_widget = tk.Scrollbar(parent, command=function)
Description: Specifies the function used to scroll the associated widget.
Example: command=text.yview
cursor
Syntax: scrollbar_widget = tk.Scrollbar(parent, cursor="cursor_type")
Description: Sets the mouse cursor.
elementborderwidth
Syntax: scrollbar_widget = tk.Scrollbar(parent, elementborderwidth=value)
Description: Sets the border width of the slider and arrow buttons.
jump
Syntax: scrollbar_widget = tk.Scrollbar(parent, jump=True)
Description: Updates the associated widget only after the slider is released.
Default: False
orient
Syntax: scrollbar_widget = tk.Scrollbar(parent, orient="vertical")
Description: Specifies the scrollbar orientation.
Valid values: "vertical", "horizontal"
Default: "vertical"
relief
Syntax: scrollbar_widget = tk.Scrollbar(parent, relief="style")
Description: Sets the border style.
Default: sunken
repeatdelay
Syntax: scrollbar_widget = tk.Scrollbar(parent, repeatdelay=milliseconds)
Description: Specifies how long to wait before auto-repeating begins.
Default: 300
repeatinterval
Syntax: scrollbar_widget = tk.Scrollbar(parent, repeatinterval=milliseconds)
Description: Specifies the interval between repeated scrolling actions.
Default: 100
takefocus
Syntax: scrollbar_widget = tk.Scrollbar(parent, takefocus=1)
Description: Determines whether the scrollbar can receive keyboard focus.
troughcolor
Syntax: scrollbar_widget = tk.Scrollbar(parent, troughcolor="color")
Description: Sets the colour of the scrollbar trough.
width
Syntax: scrollbar_widget = tk.Scrollbar(parent, width=value)
Description: Sets the width of a vertical scrollbar or the height of a horizontal scrollbar.
Default: Platform dependent

16.5. Default options

Code to display the default value for each Scrollbar option is shown below.
import tkinter as tk

root = tk.Tk()

widget = tk.Scrollbar(root)
widget_options = widget.keys()

for option in widget_options:
    print(f"{option}: {widget.cget(option)}")  # cget retrieves the current value of the option