用于多个窗口的 Tkinter 示例代码，为什么按钮无法正确加载？

我正在编写一个程序，应该：

1. 按一下按钮即可打开一个窗口。
2. 按另一个按钮关闭新打开的窗口。

我使用类，以便稍后可以将代码插入到更大的程序中。但是，我无法正确加载按钮。

import tkinter as tk

class Demo1(tk.Frame):
    def __init__(self):
        tk.Frame.__init__(self)
        self.pack()
        self.master.title("Demo 1")
        self.button1 = tk.Button(self, text = "Button 1", width = 25,
                               command = self.new_window)
        self.button1.grid(row = 0, column = 1, columnspan = 2, sticky = tk.W+tk.E+tk.N+tk.S)

    def new_window(self):
        self.newWindow = Demo2()

class Demo2(tk.Frame):
    def __init__(self):
        new = tk.Frame.__init__(self)
        new = tk.Toplevel(self)
        new.title("Demo 2")
        new.button = tk.Button(text = "Button 2", width = 25,
                               command = self.close_window)
        new.button.pack()

    def close_window(self):
        self.destroy()

def main():
    Demo1().mainloop()

if __name__ == '__main__':
    main()

我以更有条理、更实用的方式重写了你的代码：

import tkinter as tk

class Demo1:
    def __init__(self, master):
        self.master = master
        self.frame = tk.Frame(self.master)
        self.button1 = tk.Button(self.frame, text = 'New Window', width = 25, command = self.new_window)
        self.button1.pack()
        self.frame.pack()

    def new_window(self):
        self.newWindow = tk.Toplevel(self.master)
        self.app = Demo2(self.newWindow)

class Demo2:
    def __init__(self, master):
        self.master = master
        self.frame = tk.Frame(self.master)
        self.quitButton = tk.Button(self.frame, text = 'Quit', width = 25, command = self.close_windows)
        self.quitButton.pack()
        self.frame.pack()

    def close_windows(self):
        self.master.destroy()

def main(): 
    root = tk.Tk()
    app = Demo1(root)
    root.mainloop()

if __name__ == '__main__':
    main()

Result: