為什么會出現錯誤：“home_frame is not defined”，即使它已經是全局的？

Question

我正在創建一個簡單的 Tkinter GUI 應用程序，它有一個簡單的登錄頁面。 當用戶登錄時，主頁會通過三個按鈕打開：go 到頁面 A，go 到頁面 B 或注銷。 但我收到錯誤：第 75 行，在 show_login_page home_frame.pack_forget() NameError: name 'home_frame' is not defined

即使 home_frame 在第 33 行被聲明為全局的。

這是我的代碼：

import tkinter as tk

# Create the main window
window = tk.Tk()
window.title("Login")
window.geometry("300x300")

# Create the login page as a frame
login_frame = tk.Frame(window)

def check_login():
    # Get the username and password from the form
    username = username_entry.get()
    password = password_entry.get()

    # Check the login credentials
    if username == "1" and password == "1":
        # If the login is successful, destroy the login page and show the home page
        login_frame.pack_forget()
        show_home_page()
        print("Yo")
    else:
        # If the login is unsuccessful, show an error message
        error_label = tk.Label(login_frame, text="Invalid login. Please try again.")
        error_label.pack()

# Create the submit button
submit_button = tk.Button(login_frame, text="Submit", command=check_login)
submit_button.pack()

# Define the function to show the home page
def show_home_page():
    global home_frame
    # Create the home page as a frame
    home_frame = tk.Frame(window)
    home_frame.pack()
    try:
        page_a_frame.pack_forget()
        page_b_frame.pack_forget()
        login_frame.pack_forget()
    except NameError:
        pass

    # Create the buttons to navigate to the other pages
    logout_button = tk.Button(home_frame, text="Logout", command=show_login_page)
    page_a_button = tk.Button(home_frame, text="Page A", command=show_page_a)
    page_b_button = tk.Button(home_frame, text="Page B", command=show_page_b)
    logout_button.pack()
    page_a_button.pack()
    page_b_button.pack()

# Define the functions to show the other pages
def show_page_a():
    global page_a_frame
    home_frame.pack_forget()
    page_a_frame = tk.Frame(window)
    page_a_frame.pack()
    tk.Label(page_a_frame, text="This is page A").pack()
    back_button = tk.Button(page_a_frame, text="Back", command=show_home_page)
    back_button.pack()

def show_page_b():
    global page_b_frame
    home_frame.pack_forget()
    page_b_frame = tk.Frame(window)
    page_b_frame.pack()
    tk.Label(page_b_frame, text="This is page B").pack()
    back_button = tk.Button(page_b_frame, text="Back", command=show_home_page)
    back_button.pack()

# Define the function to show the login page
def show_login_page():
    global login_frame
    global home_frame
    home_frame.pack_forget()
    login_frame = tk.Frame(window)
    login_frame.pack()

    # Create the form for the user to enter their username and password
    username_label = tk.Label(login_frame, text="Username:")
    global username_entry
    username_entry = tk.Entry(login_frame, fg="blue")
    password_label = tk.Label(login_frame, text="Password:")
    global password_entry
    password_entry = tk.Entry(login_frame, show="*")

    # Place the form widgets on the login page
    username_label.pack()
    username_entry.pack()
    password_label.pack()
    password_entry.pack()

    # Create the submit button
    submit_button = tk.Button(login_frame, text="Submit", command=check_login)
    submit_button.pack()

# Show the login page
show_login_page()

# Run the main loop
window.mainloop()

Answer 1

我以前從未使用過 tkinter。

但是將下面的行添加到頂部似乎有效。

home_frame = tk.Frame(window)

在第 10 行。

編輯：更多信息-我的理解

據我了解，您僅在show_home_page function 中設置home_frame變量。

但是，您在調用home_frame.pack_forget之前調用show_home_page 。

所以，home_frame 實際上什么都不是。

只給全局變量不會分配任何東西，請參閱下面的測試

def foo(a):
    global c
    print(a)
    len(c)
    print(c)


>>> foo('adfa')
adfa
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in foo
NameError: name 'c' is not defined

如果您像我們在您的情況下所做的那樣，在頂部將某些內容分配給 c，它會將其視為某些內容，並且您不會收到not defined error 。

Answer 2

如果您仔細觀察，您會發現您首先調用了 function show_login_page() ，並且您正在嘗試使用尚未真正聲明的全局空間中的變量home_frame 。

您首先在show_home_page() function 中貼花和分配home_frame ，但在show_login_page()之后被調用，因此show_login_page()無法了解home_frame 。

因此，要解決此問題，您必須在分配login_frame變量的行下方的全局空間中聲明並分配home_frame 。

所以，最終的代碼將是這樣的：

import tkinter as tk

# Create the main window
window = tk.Tk()
window.title("Login")
window.geometry("300x300")

# Create the login page as a frame
login_frame = tk.Frame(window)
home_frame = tk.Frame(window)

def check_login():
    # Get the username and password from the form
    username = username_entry.get()
    password = password_entry.get()

    # Check the login credentials
    if username == "1" and password == "1":
        # If the login is successful, destroy the login page and show the home page
        login_frame.pack_forget()
        show_home_page()
        print("Yo")
    else:
        # If the login is unsuccessful, show an error message
        error_label = tk.Label(login_frame, text="Invalid login. Please try again.")
        error_label.pack()

# Create the submit button
submit_button = tk.Button(login_frame, text="Submit", command=check_login)
submit_button.pack()

# Define the function to show the home page
def show_home_page():
    # Create the home page as a frame
    home_frame.pack()
    try:
        page_a_frame.pack_forget()
        page_b_frame.pack_forget()
        login_frame.pack_forget()
    except NameError:
        pass

    # Create the buttons to navigate to the other pages
    logout_button = tk.Button(home_frame, text="Logout", command=show_login_page)
    page_a_button = tk.Button(home_frame, text="Page A", command=show_page_a)
    page_b_button = tk.Button(home_frame, text="Page B", command=show_page_b)
    logout_button.pack()
    page_a_button.pack()
    page_b_button.pack()

# Define the functions to show the other pages
def show_page_a():
    global page_a_frame
    home_frame.pack_forget()
    page_a_frame = tk.Frame(window)
    page_a_frame.pack()
    tk.Label(page_a_frame, text="This is page A").pack()
    back_button = tk.Button(page_a_frame, text="Back", command=show_home_page)
    back_button.pack()

def show_page_b():
    global page_b_frame
    home_frame.pack_forget()
    page_b_frame = tk.Frame(window)
    page_b_frame.pack()
    tk.Label(page_b_frame, text="This is page B").pack()
    back_button = tk.Button(page_b_frame, text="Back", command=show_home_page)
    back_button.pack()

# Define the function to show the login page
def show_login_page():
    global login_frame
    global home_frame
    home_frame.pack_forget()
    login_frame = tk.Frame(window)
    login_frame.pack()

    # Create the form for the user to enter their username and password
    username_label = tk.Label(login_frame, text="Username:")
    global username_entry
    username_entry = tk.Entry(login_frame, fg="blue")
    password_label = tk.Label(login_frame, text="Password:")
    global password_entry
    password_entry = tk.Entry(login_frame, show="*")

    # Place the form widgets on the login page
    username_label.pack()
    username_entry.pack()
    password_label.pack()
    password_entry.pack()

    # Create the submit button
    submit_button = tk.Button(login_frame, text="Submit", command=check_login)
    submit_button.pack()

# Show the login page
show_login_page()

# Run the main loop
window.mainloop()

我運行了這個程序..它可以工作，但它仍然有一些你必須注意的布局錯誤。 祝你好運:)