Tkinter - 如何使用停止按钮停止循环? [英] Tkinter - How to stop a loop with a stop button?

问题描述

我有这个程序，它每秒都会发出哔哔声，直到它停止.问题是，在我按下开始"并发出蜂鸣声后，我无法单击停止"按钮，因为窗口冻结了.欢迎任何帮助.

I have this program which beeps every second until it's stopped. The problem is that after I press "Start" and the beeps starts, I cannot click the "Stop" button because the window freezes. Any help is welcome.

#!/usr/bin/python
import Tkinter, tkMessageBox, time, winsound, msvcrt

running = True

Freq = 2500
Dur = 150

top = Tkinter.Tk()
top.title('MapAwareness')
top.geometry('200x100') # Size 200, 200

def start():
    sec = 0
    while running:
        if sec % 1 == 0:
            winsound.Beep(Freq, Dur)

        time.sleep(1)
        sec += 1

def stop():
    running = False

startButton = Tkinter.Button(top, height=2, width=20, text ="Start", command = start)
stopButton = Tkinter.Button(top, height=2, width=20, text ="Stop", command = stop)

startButton.pack()
stopButton.pack()

top.mainloop()

推荐答案

您的代码有几个问题.首先，您不应该在 Tkinter 程序中使用 time.sleep()，因为它会干扰 mainloop().相反，通常使用通用小部件方法 .after() 安排函数在指定的延迟后运行.

There are several things wrong with your code. First of all you shouldn't use time.sleep() in a Tkinter program because it interferes with the mainloop(). Instead one typically uses the universal widget method .after() to schedule a function to run after a specified delay.

其次，您没有正确使用全局变量.当您为函数中的命名变量赋值时，它将创建一个局部变量，除非该名称之前已声明为global.例如，您的 stop() 函数正在创建一个名为 running 的局部变量并将其值设置为 0，不改变同名的全局变量.

Secondly you're not using global variables correctly. When you assign a value to a named variable in a function, it will create a local variable unless that name has been previous declared global. So for instance, your stop() function is creating a local variable named running and setting its value to 0, not changing the value of the global variable with the same name.

上一条规则不适用于仅引用(读取)变量的当前值.这就是为什么在 start() 中没有声明 Freq 和 Dur 全局变量是可以的.

The previous rule doesn't apply to just referencing (reading) the current value of a variable. That is why it was OK to not have declared Freq and Dur globals in start().

另一个问题是start() 函数中的sec % 1 == 0.任何值 %1 都是 0.要检查奇数/偶数，请使用 sec % 2.

Another problem is with the sec % 1 == 0 in your start() function. Any value % 1 is 0. To check odd/evenness use sec % 2.

这是一个工作版本，它也被重新格式化以遵循 PEP 8 - 风格指南更接近于 Python 代码.

Here's a working version which has also been reformatted to follow PEP 8 - Style Guide for Python Code more closely.

try:
    import tkinter as tk
except ModuleNotFoundError:
    import Tkinter as tk  # Python 2.
import time
import winsound

FREQ = 2500
DUR = 150

after_id = None
secs = 0

def beeper():
    global after_id
    global secs

    secs += 1
    if secs % 2 == 0:  # Every other second.
        winsound.Beep(FREQ, DUR)
    after_id = top.after(1000, beeper)  # Check again in 1 second.

def start():
    global secs

    secs = 0
    beeper()  # Start repeated checking.

def stop():
    global after_id

    if after_id:
        top.after_cancel(after_id)
        after_id = None


if __name__ == '__main__':

    top = tk.Tk()
    top.title('MapAwareness')
    top.geometry('200x100')

    startButton = tk.Button(top, height=2, width=20, text="Start", command=start)
    stopButton = tk.Button(top, height=2, width=20, text="Stop", command=stop)
    startButton.pack()
    stopButton.pack()

    top.mainloop()

更新

既然这个答案已经变得相当流行，我想谈谈另一个稍微更高级的话题——即如何通过消除几乎所有全局变量的需要，使代码更加面向对象来简化事情.

Update

Since this answer has become fairly popular, I'd like touch on another slightly more advanced topic — namely how making the code more object-oriented would simplify things by eliminating the need almost all of the global variables.

try:
    import tkinter as tk
except ModuleNotFoundError:
    import Tkinter as tk  # Python 2.
import time
import winsound

FREQ = 2500
DUR = 150

class Application(tk.Frame, object):
    def __init__(self, master=None):
        super(Application, self).__init__(master)  # Call baseclass constructor.
        self.after_id = None
        self.secs = 0

        # Create widgets,
        startButton = tk.Button(top, height=2, width=20, text="Start", command=self.start)
        stopButton = tk.Button(top, height=2, width=20, text="Stop", command=self.stop)
        startButton.pack()
        stopButton.pack()

    def beeper(self):
        self.secs += 1
        if self.secs % 2 == 0:  # Every other second.
            winsound.Beep(FREQ, DUR)
        self.after_id = top.after(1000, self.beeper)  # Check again in 1 second.

    def start(self):
        self.secs = 0
        self.beeper()  # Start repeated checking.

    def stop(self):
        if self.after_id:
            top.after_cancel(self.after_id)
            self.after_id = None


if __name__ == '__main__':

    top = tk.Tk()
    app = Application()
    app.master.title('MapAwareness')
    app.master.geometry('200x100')
    app.mainloop()

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