如何在 tkinter 画布中停止草图

Question

我在这里有几行代码在tkinter canvas 中画了一个圆圈，但我想做的是将草图停止到它开始的位置，所以我使用睡眠，但我在它到达的地方停止草图继续。

所以我写了这个函数

def stop_extent():

    canvas.create_arc(0, 0, 0, 0, extent=0, outline="red", tags=("arc",))
    extent = float(canvas.itemcget("arc", "extent"))
    extent = extent + 5.0
    canvas.itemconfigure("arc", extent=extent)
    canvas.after(100, stop_extent)

并将所有值设置为0，但它仍然没有停止它并且标签也没有配置。

import tkinter as tk
import time



def change_extent():
    l.config(text="sketch in progress...")

    canvas.create_arc(350, 100, 220, 220, extent=0, outline="yellow", tags=("arc",))
    extent = float(canvas.itemcget("arc", "extent"))
    extent = extent + 5.0
    canvas.itemconfigure("arc", extent=extent)
    canvas.after(100, change_extent)



def stop_extent():
    l.config(text="sketch stopped...")
    time.sleep(10)
    l.config(text="sketch stopped...")


root = tk.Tk()
root.geometry("600x400")

canvas = tk.Canvas(root, width=200, height=200, background="dodger blue")
canvas.pack(fill="both", expand=True)


l = tk.Label(canvas, bg="dodger blue",  fg="white")
l.place(x=250, y=20)


b= tk.Button(canvas, text="Start sketch", command=change_extent, width=25, fg='dodger blue')
b.place(x=220, y=330)


b= tk.Button(canvas, text="stop sketch", command=stop_extent, width=25, fg='dodger blue')
b.place(x=220, y=370)


root.mainloop()

Answer 1

可以在change_extent方法中跟踪canvas.after产生的回调，在stop_extent方法中用canvas.after_cancel取消；在下面的示例中，我使用一个全局变量stop 来演示它。

在 GUI 应用程序中使用 time.sleep 通常是个坏主意。

您也不需要在每次要修改其范围时重新创建弧，但这超出了您的问题范围。

import tkinter as tk
import time


def change_extent():
    global stop
    l.config(text="sketch in progress...")
    extent = float(canvas.itemcget(arc_item, "extent"))
    canvas.itemconfigure("arc", extent=extent+5)
    stop = canvas.after(100, change_extent)


def stop_extent():
    l.config(text="sketch stopped...")
    print(stop)
    canvas.after_cancel(stop)
    canvas.itemconfigure("arc", extent=0)   # <- reset to straight line start



stop = None
root = tk.Tk()
root.geometry("600x400")

canvas = tk.Canvas(root, width=200, height=200, background="dodger blue")
canvas.pack(fill="both", expand=True)

arc_item = canvas.create_arc(350, 100, 220, 220, extent=0, outline="yellow", tags=("arc",))


l = tk.Label(canvas, bg="dodger blue",  fg="white")
l.place(x=250, y=20)


b= tk.Button(canvas, text="Start sketch", command=change_extent, width=25, fg='dodger blue')
b.place(x=220, y=330)


b= tk.Button(canvas, text="stop sketch", command=stop_extent, width=25, fg='dodger blue')
b.place(x=220, y=370)


root.mainloop()