为什么Tkinter滚动条仅在您将鼠标悬停在其上时才会激活？

Question

我正在使用Tkinter创建一个GUI，只有当我将鼠标放在它上面并滚动时，滚动条才会激活。当鼠标不在滚动条上和窗口中间时，有没有办法让鼠标滚轮滚动？

import Tkinter as Tk
from Tkinter import StringVar

class Example(Tk.Frame):
    def __init__(self, root):

        Tk.Frame.__init__(self, root)
        self.canvas = Tk.Canvas(root, width=200, heigh=200,  borderwidth=0, background="#ffffff")
        self.frame = Tk.Frame(self.canvas,background="#ffffff")
        self.vsb = Tk.Scrollbar(root, orient="vertical", command=self.canvas.yview)
        self.canvas.configure(yscrollcommand=self.vsb.set)

        self.vsb.pack(side="right", fill="y")
        self.canvas.pack(side="left", fill="both", expand=True)
        self.canvas.create_window((10,10), window=self.frame, anchor="nw", 
                                  tags="self.frame")

        self.frame.bind("<Configure>", self.OnFrameConfigure)

        self.populate()

    def populate(self):


#####Last Name######
        labelText=StringVar()
        labelDir=Tk.Label(self.frame, text='hello').grid(row=1, column=1)
        labelDir


        labelText=StringVar()
        labelDir1=Tk.Label(self.frame, text='hello').grid(row=2, column=2)
        labelDir1

        labelText=StringVar()
        labelDir2=Tk.Label(self.frame, text='hello').grid(row=1, column=1)
        labelDir2


        directory=StringVar(None)
        self.can_lname =Tk.Entry(self.frame, text=directory,width=100).grid(row=4, column=4)
        self.can_lname

    def OnFrameConfigure(self, event):
        '''Reset the scroll region to encompass the inner frame'''
        self.canvas.configure(scrollregion=self.canvas.bbox("all"))

if __name__ == "__main__":
    root=Tk.Tk()
    Example(root).pack(side="top", fill="both", expand=True)
    root.mainloop()