用 TK 写的状态条为何不能实时显示出状态 ？

class ProgressBar:     def __init__(self, Parent, Height=14, Width=100, ForegroundColor=None, BackgroundColor=None, Progress=0):         self.Height = Height         self.Width = Width         self.BarCanvas = Tkinter.Canvas(Parent, width=Width, height=Height, background=BackgroundColor, borderwidth=1, relief=Tkinter.SUNKEN)         if (BackgroundColor):             self.BarCanvas['backgroundcolor'] = BackgroundColor         self.BarCanvas.pack(expand=Tkinter.YES, fill=Tkinter.X, padx=0, pady=0)         self.RectangleID = self.BarCanvas.create_rectangle(0,0,0,Height)         if (ForegroundColor == None):             ForegroundColor = "black"         self.BarCanvas.itemconfigure(self.RectangleID, fill=ForegroundColor)         self.SetProgressPercent(Progress)                     self.SetProgressPercent(int(item))              def SetProgressPercent(self, NewLevel):         self.Progress = NewLevel         self.Progress = min(100, self.Progress)         self.Progress = max(0, self.Progress)         self.DrawProgress()     def DrawProgress(self):         rogressPixel = (self.Progress/100.0)*self.Width         self.BarCanvas.coords(self.RectangleID, 0, 0, ProgressPixel, self.Height)     def GetProgressPercent(self):         return self.Progress

调用：
self.root = Tkinter.Tk()
MainFrame = Tkinter.Frame(self.root)
self.Bar = ProgressBar(MainFrame)
....
self.Bar.SetProcessPercent(10)

在程序中做别的事情的时候，调用self.Bar.SetProcessPercent时屏幕上并不显示当时的进度条，都完成了才显示出来，改成线程模式也不行 。。。这是为何？

谢谢