How to use slider.on_changed() within a class in Tkinter in Python

I'm trying to use a horizontal slider to change the xlim of my plot. But first, I can't figure out how to get the slider to update using the on_changed() method. I don't have a strong understanding of how classes, and objects interact with each other.

I'm using this slider example as a template:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider, Button, RadioButtons

fig, ax = plt.subplots()
plt.subplots_adjust(left=0.25, bottom=0.25)
t = np.arange(0.0, 1.0, 0.001)
a0 = 5
f0 = 3
delta_f = 5.0
s = a0 * np.sin(2 * np.pi * f0 * t)
l, = plt.plot(t, s, lw=2)
ax.margins(x=0)

axcolor = 'lightgoldenrodyellow'
axfreq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
axamp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=axcolor)

sfreq = Slider(axfreq, 'Freq', 0.1, 30.0, valinit=f0, valstep=delta_f)
samp = Slider(axamp, 'Amp', 0.1, 10.0, valinit=a0)


def update(val):
    amp = samp.val
    freq = sfreq.val
    l.set_ydata(amp*np.sin(2*np.pi*freq*t))
    fig.canvas.draw_idle()


sfreq.on_changed(update)
samp.on_changed(update)

resetax = plt.axes([0.8, 0.025, 0.1, 0.04])
button = Button(resetax, 'Reset', color=axcolor, hovercolor='0.975')


def reset(event):
    sfreq.reset()
    samp.reset()
button.on_clicked(reset)

rax = plt.axes([0.025, 0.5, 0.15, 0.15], facecolor=axcolor)
radio = RadioButtons(rax, ('red', 'blue', 'green'), active=0)


def colorfunc(label):
    l.set_color(label)
    fig.canvas.draw_idle()
radio.on_clicked(colorfunc)

plt.show()

The part that I'm having trouble implementing in my app is:

sfreq.on_changed(update)
samp.on_changed(update)

It works fine if you're opening a plot using plt.show(), but if you're packing it into a canvas like I'm doing below, it stops working. Any ideas why?

Here is the code for my app: UPDATE: I simplified the code to focus on the problem.

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider, Button, RadioButtons
from matplotlib.figure import Figure
from matplotlib.backends.backend_tkagg import(FigureCanvasTkAgg, NavigationToolbar2Tk)

from tkinter import *
import tkinter as tk

global running
running = True

global graph_exists
graph_exists = False

class MyApp:
    def __init__(self, parent):
        self.myParent = parent ###remember my parent, the root
        self.sfreq = 0
        self.samp = 0

        
        
    def run(self):
        self.fig, self.ax = plt.subplots()
        plt.subplots_adjust(left=0.25, bottom=0.25)
        self.t = np.arange(0.0, 1.0, 0.001)
        a0 = 5
        f0 = 3
        delta_f = 5.0
        s = a0 * np.sin(2 * np.pi * f0 * self.t)
        self.l, = plt.plot(self.t, s, lw=2)
        self.ax.margins(x=0)

        axcolor = 'lightgoldenrodyellow'
        axfreq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
        axamp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=axcolor)

        self.sfreq = Slider(axfreq, 'Freq', 0.1, 30.0, valinit=f0, valstep=delta_f)
        self.samp = Slider(axamp, 'Amp', 0.1, 10.0, valinit=a0)

        canvas = FigureCanvasTkAgg(self.fig, root)
        canvas.draw()
        canvas.get_tk_widget().pack(side=tk.TOP, fill=tk.BOTH, expand=1)
        graph_exists = True

        

    def update(self, val):
        amp = self.samp.val
        freq = self.sfreq.val
        self.l.set_ydata(amp*np.sin(2*np.pi*freq*self.t))
        self.fig.canvas.draw_idle()

    if graph_exists:
        self.sfreq.on_changed(update)
        self.samp.on_changed(update)
        

#Run the event loop
root = tk.Tk()
myapp = MyApp(root)
myapp.run()
root.mainloop()

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