label2=tkinter.Label(self.win,text='请选择时间间隔：').place(x=40,y=20)
    self.cv=tkinter.StringVar()
    self.com=ttk.Combobox(self.win,textvariable=self.cv)
    self.com.place(x=190,y=20)
    self.com['value']=("15分钟","30分钟","45分钟","60分钟")
    self.com.current(0)
    self.com.bind("<<ComboboxSelected", self.get_time)
        
  def get_time(self,event):

    self.minute=int(self.com.get()[:-2])

    button=tkinter.Button(self.win,text="开始",command=self.alarm,width=6,height=1)
    button.place(x=40,y=60)
    button2=tkinter.Button(self.win,text="暂停",command=self.pause,width=6,height=1)
    button2.place(x=180,y=60)   
    button3=tkinter.Button(self.win,text="继续",command=self.go_on,width=6,height=1)
    button3.place(x=320,y=60) 
        
  def alarm(self):
    
    self.now=datetime.datetime.now()
    delta=datetime.timedelta(minutes=self.minute)
    self.target=self.now+delta
    self.win.after(0,self.update)
    
  def pause(self):
    
    self.pause_time=datetime.datetime.now()
    self.flag=True
    self.win.after_cancel()
    
  def go_on(self):
    
    self.go_on_now=datetime.datetime.now()
    self.pause_long=self.go_on_now-self.pause_time+self.pause_long
    self.flag=False
    self.win.after(0,self.update)

  def update(self):
    
    now=datetime.datetime.now()
    countdown=self.target-now+self.pause_long
    self.label=tkinter.Label(self.win,text=str(countdown)[:7],font=("黑体",70))
    self.label.place(x=60,y=130)
    if str(countdown)[:7]=='0:00:00':
      tkinter.messagebox.showwarning(title="FBIWarning",message="您已工作{}分钟,请马上离开座位休息片刻！".format(self.minute))
      self.flag=True
      self.win.after_cancel()
    if self.flag==False:
      self.win.after(1,self.update)