Labels Added via Button Command Not Expanding Frame-CodePudding

I am trying to dynamically add labels to a frame contained within a canvas, for scrollbar capability. The labels are being added via a function that is called from a button. The function works fine if called on startup, the frame updates as expected and I have scrollbar capabilities. If I call the function from the button command the frame updates with the labels, but only up to the limit of the starting frame/canvas size. The additional area of the frame containing the rest of the labels won't be visible as the scrollbar isn't "activated"

I tried searching but couldn't find this question being asked before. I am new to Python and Tkinter so apologies if I'm missing something obvious.

from tkinter import *
from tkinter import ttk

root = Tk()
root.geometry("550x550")

main_frame = Frame(root)
main_frame.grid(row = 0, column = 0)

button_frame = Frame(root)
button_frame.grid(row = 1, column = 0)

image_canvas_0 = Canvas(main_frame, height = 500, width = 500)
image_canvas_0.grid(row = 0, column = 0)

image_canvas_0_scrollbar = ttk.Scrollbar(main_frame, orient = VERTICAL, command = image_canvas_0.yview)
image_canvas_0_scrollbar.grid(column = 1, row = 0, sticky = (N,S))

image_canvas_0.config(yscrollcommand = image_canvas_0_scrollbar.set)
image_canvas_0.bind('<Configure>', lambda e: image_canvas_0.configure(scrollregion = image_canvas_0.bbox("all")))

second_frame = Frame(image_canvas_0)
image_canvas_0.create_window((0,0), window = second_frame, anchor = 'nw')

def test_function(*args):
    for i in range(100):
        label_text = 'test'   str(i)
        Label(second_frame, text = label_text).grid(row = i, column = 0)

func_button = Button(button_frame, text = 'Click Me', command = test_function)
func_button.grid(row = 0, column =  0)

#test_function()

root.mainloop()

CodePudding user response：

You aren't changing the scrollregion after you've added widgets to the frame. The canvas doesn't know that there's new data that should be scrollable.

Normally this is done by adding a bind to the frame's <Configure> event, since that event fires whenever the frame changes size.

second_frame.bind("<Configure>", lambda e: image_canvas_0.configure(scrollregion = image_canvas_0.bbox("all")))

The reason your code seems to work when calling the function directly at startup is that you have a similar binding on the canvas itself, which automatically fires once the widget is actually shown on the screen. That happens after you call test_function() when mainloop first starts to run. Once the program starts, the canvas <Configure> event doesn't fire a second time.