How to test to see if a top-level window is open?

Question

I'm feeling somewhat like Python programming may not be my thing....

I have created a tkinter GUI that uses a button callback to open another window (other searches say this window should be a top-level window) and it works pretty good, how-ever each time the button is pressed it opens another identical (as far as I can tell) window.

Question: how can I test to see if a window (opened with the button) already exists and thus prevent duplicates from being generated???

NOTE: I am not (yet) a OOP programmer so please avoid that paradigm if possible...

regards,

Bill W.

Answer 1

I am not (yet) a OOP programmer so please avoid that paradigm if possible...

Sooner or later, you'll have to understand object-oriented programming if you want to program in Python successfully. The alternative (global variables and functions everywhere) is not definitely a good approach. Even Tkinter has lots of classes with its respective methods, so it looks like it is necessary for your purpose.

Back to your question, a solution could be setting the Toplevel window as an attribute of a class where you wrap all your application, and only open a new window if this attribute is None. To set this attribute to None when you close the window, you can use the protocol method to set a callback.

This is a small working example where you can see how it would work:

import Tkinter as tk

class App(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)
        self.button = tk.Button(self, text="Open a new window", command=self.openwindow)
        self.button.pack()
        self.toplevel = None
    def openwindow(self):
        if self.toplevel is None:
            self.toplevel = tk.Toplevel(self)
            self.toplevel.protocol('WM_DELETE_WINDOW', self.removewindow)
    def removewindow(self):
        self.toplevel.destroy()
        self.toplevel = None

app = App()
app.mainloop()

Answer 2

You can use this method winfo_exists() to check if the window exists.

if the return value is 0, it means the window doesn't exist.

if the return value is 1, it means the window exists.

Sample Code...

from tkinter import *

mainWindow = Tk()
mainWindow.title("This is main Window")

# create a top-level window
newWindow = Toplevel(mainWindow)
newWindow.title("This is Toplevel window")

print("Before destroying window = " + str(newWindow.winfo_exists()))
newWindow.destroy()
print("After destroying window = " + str(newWindow.winfo_exists()))

mainloop()

Output is...

# Before destroying window = 1
# After destroying window = 0