如何跨多个文件创建不同的Tkinter框架？

Question

I am creating a GUI on Tkinter that needs to open or close windows when buttons are pressed, and I would prefer if each window was in its own file. I tried creating a very simple example of this with the three files below. The first window is supposed to have a button that, when pressed, closes the current window and opens the next one. I'm currently running into a problem where the window is created but the button is not. How do I fix this?

Main.py

from MyTkWindow import *

myWindow = MyTkWindow()
myWindow.start()

MyTkWindow.py

import tkinter as tk
from NextFrame import *

class MyTkWindow(tk.Frame):
    def __init__(self, parent=None):
        tk.Frame.__init__(self)
        nextWin = NextWindow()
        NextScreen = tk.Button(self, text="Next", command=lambda:[self.destroy(), nextWin.start()])
        NextScreen.pack()

    def start(self):
        self.mainloop()

NextFrame.py

import tkinter as tk

class NextWindow(tk.Frame):
    def __init__(self, parent=None):
        tk.Frame.__init__(self)
        Leave = tk.Button(self, text="Quit", command=lambda: self.destroy())
        Leave.pack()

    def start(self):
        self.mainloop()

Answer 1

I got this to work with the indicated changes. The primary problem was due to not calling the pack() method of the windows/frames being created.

main.py :

from MyTkWindow import *

myWindow = MyTkWindow()
myWindow.pack()  # ADDED

myWindow.start()

MyTkWindow.py :

import tkinter as tk
from NextFrame import *

class MyTkWindow(tk.Frame):
    def __init__(self, parent=None):
        tk.Frame.__init__(self, parent)  # ADDED parent argument.
        nextWin = NextWindow()
        NextScreen = tk.Button(self, text="Next",
                               command=lambda: [self.destroy(),
                                                nextWin.pack(),  # ADDED
                                                nextWin.start()])
        NextScreen.pack()

    def start(self):
        self.mainloop()

NextFrame.py :

import tkinter as tk

class NextWindow(tk.Frame):
    def __init__(self, parent=None):
        tk.Frame.__init__(self, parent)  # ADDED parent argument.
        Leave = tk.Button(self, text="Quit",
                          command=lambda: self.destroy())
        Leave.pack()

    def start(self):
        self.mainloop()

Suggestion: Read and start following the PEP 8 - Style Guide for Python Code because it will make your code more understanable and maintainable. Specifically, the Naming Conventions section especially with respect to class, variable, and module file names.