如何让tkinter combobox循环在类中工作，使用列表作为默认值，并在下拉菜单中使用一个字典？

import tkinter as tk
from tkinter import ttk

class MyApp(tk.Tk):
    def __init__(self):
        super().__init__()
        self.title("My App")
        self.geometry("200x100")
        self.create_widgets()

    def create_widgets(self):
        self.combobox = ttk.Combobox(self, values=list(my_dict.keys()))
        self.combobox.set(list(my_dict.keys())[0])
        self.combobox.bind("<<ComboboxSelected>>", self.on_combobox_selected)
        self.combobox.pack()

    def on_combobox_selected(self, event):
        selected_value = self.combobox.get()
        selected_item = my_dict[selected_value]
        print(selected_item)

my_dict = {"Option 1": "Value 1", "Option 2": "Value 2", "Option 3": "Value 3"}

app = MyApp()
app.mainloop()