Can't invoke "button" command: application has been destroyed

Question

with an error which is impossible to fix under my hands. I find a defined variable after it has been opened I want the page to close so not all windows are open however when I load new user screen once they have done filled in new user details, I put a button in to which it will redirect them to existingUserEntry page ,which it is saying it cannot invoke the button, any help is necessary thanks?

def existingUserEntry():
    intitialScreen.destroy()
    login = False
    global existingUserScreen, usernameEntry, passwordEntry  
    existingUserScreen = Tk() # Set up a screen
    existingUserScreen.title("Existing User Login Screen")# Set a caption
    existingUserScreen.config(bg = "WHITE")# Set the background colour
    existingUserScreen.geometry("350x150")# Set the size of the window
    # Code for the username entry box.    
    usernameLabel = Label(existingUserScreen, text = "User name:")# Username Text box
    usernameLabel.config(bg = "PALE GREEN", font=('Helvetica', 12))# Formatting Features
    usernameLabel.pack()
    usernameEntry = ttk.Entry(existingUserScreen, font = "bold", width = 30)
    usernameEntry.pack()
    # Code for the password entry box.
    passwordLabel = Label(existingUserScreen, text = "Password:")# Password Text box
    passwordLabel.config(bg = "PALE GREEN", font=('Helvetica', 12))# Formatting Features
    passwordLabel.pack()
    passwordEntry = ttk.Entry(existingUserScreen, font = "bold", width = 30, show="*")
    passwordEntry.pack() 
    # Code for the sign in button.
    signInButton = Button(existingUserScreen, text="Sign in", width=10, command=verifyLoginDetails)
    signInButton.pack(expand = 1)# Placement of the Sign In button
    existingUserScreen.mainloop()

#Code for a button to allow new users to login to profile after creating one
    newUserSignInButton = Button(newUserScreen, text=" Back to Login Screen", width=15, command=backToLoginScreen)
    newUserSignInButton.config(height= 1, width= 40)
    newUserSignInButton.pack(expand= 4)
    newUserScreen.mainloop()
    newUserScreen = Button(intitialScreen, text="Existing User Sign In", width=25, command=existingUserEntry)

score 1 · Answer 1 · edited May 23 '17 at 12:13

def existingUserEntry():
    intitialScreen.destroy()
    ....
    newUserScreen = Button(intitialScreen,...)

You are destroying your intitialScreen at the beginning of your method then trying to add a button to that container at the end which causes the error. You need to choose existing one for your widgets.

Also, please note that,

Don't create multiple Tk() instances. If you want another window (e.g. pop-up) use Toplevel() instead of Tk(). (There is only one Tk() in this code but it feels like you have more in your actual code)
If you don't know what you are exactly doing, you most likely don't want to use mainloop() anywhere but at the end of your program.

Can't invoke "button" command: application has been destroyed

1 Answers1