无法滚动画布Tkinter

import tkinter as tk

def scroll_canvas(event):
    canvas.yview_scroll(-1 * int((event.delta / 120)), "units")

root = tk.Tk()
root.geometry("400x300")

# 创建一个滚动条
scrollbar = tk.Scrollbar(root)
scrollbar.pack(side=tk.RIGHT, fill=tk.Y)

# 创建一个画布，并设置滚动条
canvas = tk.Canvas(root, yscrollcommand=scrollbar.set)
canvas.pack(side=tk.LEFT, fill=tk.BOTH, expand=True)

# 将滚动条与画布关联
scrollbar.config(command=canvas.yview)

# 创建一个框架，用于放置画布内的内容
frame = tk.Frame(canvas)
canvas.create_window((0, 0), window=frame, anchor="nw")

# 添加一些内容到框架中
for i in range(50):
    label = tk.Label(frame, text=f"Label {i}")
    label.pack()

# 绑定鼠标滚轮事件
canvas.bind_all("<MouseWheel>", scroll_canvas)

root.mainloop()