更多关于tkinter选项菜单首选项消失的问题

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这是我之前提问的后续内容，链接在这里。我想用ttk.OptionMenu来改善下拉菜单的外观和感觉。但是在这篇帖子中提到，“ttk选项菜单一开始会显示所有的值在下拉框里。选择任何一个值后，列表中的第一个值就会消失，再也不会出现了……” 解决这个问题的方法是往列表里添加一个空项。在我的情况下，因为我使用的是字典，所以在字典的第一项添加'':[]解决了这个问题。这是唯一的解决方案吗？我不想在我的字典里加一个多余的东西。以下是代码：

import tkinter as tk
from tkinter import ttk
from tkinter import messagebox

class App:

    def __init__(self, master):

        master.title("Continental System")

        self.dict = {'':[], 'Asia': ['Japan', 'China', 'Malasia'],
                     'Europe': ['Germany', 'France', 'Switzerland'],
                     'Africa': ['Nigeria', 'Kenya', 'Ethiopia']}
        self.frame1 = ttk.Frame(master)
        self.frame1.pack()
        self.frame2 = ttk.Frame(master)
        self.frame2.pack()
        self.variable_a = tk.StringVar()
        self.variable_b = tk.StringVar()
        self.variable_a.trace('w', self.updateoptions)
        self.optionmenu_a = ttk.OptionMenu(self.frame1, self.variable_a, *self.dict.keys())
        self.variable_a.set("Asia")
        self.optionmenu_a.grid(row = 0, column = 0)
        self.optionmenu_b = ttk.OptionMenu(self.frame1, self.variable_b, '')
        self.optionmenu_b.grid(row = 0, column = 1)
        self.btn = ttk.Button(self.frame2 , text="Submit", width=8, command=self.submit)
        self.btn.grid(row=0, column=1, padx=20, pady=20)

    def updateoptions(self, *args):
        countries = self.dict[self.variable_a.get()]
        self.variable_b.set(countries[0])
        menu = self.optionmenu_b['menu']
        menu.delete(0, 'end')
        for country in countries:
            menu.add_command(label=country, command=lambda country=country: self.variable_b.set(country))

    def submit(self, *args):
        var1 = self.variable_a.get()
        var2 = self.variable_b.get()
        if messagebox.askokcancel("Confirm Selection", "Confirm your selection: " + var1 + ' ' + var2 + ". Do you wish to continue?"):
            print(var1, var2)

    def set_window(self, *args):
        w = 800 
        h = 500
        ws = root.winfo_screenwidth()
        hs = root.winfo_screenheight()
        x = (ws/2) - (w/2)
        y = (hs/2) - (h/2)
        root.geometry('%dx%d+%d+%d' % (w, h, x, y))


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

另外，我还收到了几个错误信息，包括AttributeError: 'App' object has no attribute 'optionmenu_b'，这个问题在我上面提到的第一个问题的回答中似乎已经解决了。

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Python34\lib\tkinter\__init__.py", line 1487, in __call__
    return self.func(*args)
  File "C:\Python34\tk1_version2.py", line 32, in updateoptions
    menu = self.optionmenu_b['menu']
AttributeError: 'App' object has no attribute 'optionmenu_b'

Python版本 3.4.1

tkinter 错误处理字典用户界面设计动态更新下拉菜单 ttk optionmenu

更多关于tkinter选项菜单首选项消失的问题

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