无法在Tkinter的顶级容器中包含小部件

Question

I have code using Tkinter that opens one window, then (after clicking a button) opens a Toplevel container. I'm trying to put an Label widget into this additional window, but keep getting an error saying "can't invoke label command: application has been destroyed."

How can I keep my root.Tk() window open to avoid this error?

Here's what my code looks like:

import Tkinter
from Tkinter import *

root = Tk()
root.wm_title("First Window")


NewWin = Button(root, text="Click Me!", command=newwin)
NewWin.pack()


def newwin():
    top = Toplevel()
    top.wm_title("Second Window")

Praise = Label(top, text="Good Work!")
Praise.grid()


root.mainloop()

Up until the label I try to install in the second window, the code works. How can I keep both windows up and running?

Answer 1

The problem is that local variables are not visible to wider scopes. Therefore, the top reference does not exist as far as the rest of the program is concerned. The easiest option is to put all of that window's logic into the function that creates it.

from Tkinter import *

root = Tk()
root.wm_title("First Window")

def new_win():
    top = Toplevel()
    top.wm_title("Second Window")
    praise = Label(top, text="Good Work!")
    praise.grid()

new_win_button = Button(root, text="Click Me!", command=new_win)
new_win_button.pack()

root.mainloop()

You could also go to an OO approach and simply save references to all relevant objects within the application:

from Tkinter import *

class App(object):
    def __init__(self, parent):
        self.parent = parent
        parent.wm_title("First Window")
        self.new_win_button = Button(root, text="Click Me!", command=self.new_win)
        self.new_win_button.pack()
        self.populate_button = Button(root, text="Populate", command=self.populate)
        self.populate_button.pack()
    def new_win(self):
        self.top = Toplevel()
        self.top.wm_title("Second Window")
    def populate(self):
        self.praise = Label(self.top, text="Good Work!")
        self.praise.grid()

root = Tk()
app = App(root)
root.mainloop()

I've also cleaned up your variable names so that they don't look like class names (eg MyClass vs. my_label ).