python - 为什么我的 tkinter 椭圆形速度固定但仍会加速？

Question

我正在尝试使用 tkinter 使这个椭圆在 Canvas 上流畅地移动，但尽管速度固定，但我移动得越多，它似乎就会加速。即使在调试时，我也注意到我的速度变量不会增加到超过所需值。我无法确定是什么导致了这种加速，有人可以指出发生了什么吗？

这是我的代码:

from tkinter import*

window = Tk()
canvas = Canvas(window, width = 300, height = 300, bg ='white')
canvas.focus_set()

speedx = 0
speedy = 0
speed = 1

x1=40
y1=40

oval=canvas.create_oval(x1-10,y1-10,x1+10,y1+10,width=2,fill='orange')

def key_press(event):
    global x1, y1
    global speedx, speedy, speed

    button = event.keysym
    if button == 'Up':
        speedx = 0
        speedy = -speed
    elif button == 'Down':
        speedx = 0
        speedy = speed
    elif button == 'Right':
        speedx = speed
        speedy = 0
    elif button == 'Left':
        speedx = -speed
        speedy = 0
    move()

def move():
    global x1,y1
    global oval
    global speedx, speedy
    x1 += speedx
    y1 += speedy
    canvas.delete(oval)
    oval = canvas.create_oval(x1+10,y1-10,x1-10,y1+10,width=2,fill='orange')
    window.after(10, move)

def key_release(event):
    global speedx, speedy
    speedx = 0
    speedy = 0


canvas.bind('<KeyPress>', key_press)
canvas.bind("<KeyRelease>", key_release)
canvas.pack(padx =5, pady =5)
window.mainloop()

Answer 1

问题是你调用window.after(10, move)从你的move内部功能而无需再次取消。这会生成一个永无休止的循环调用 move对于每个 <KeyPress>事件。

你可以做的就是保存 after调用一个变量。这样您就可以确保move不会从此循环外部再次调用，另外您可以使用它来取消 after调用按键释放:

from tkinter import *

window = Tk()
canvas = Canvas(window, width = 300, height = 300, bg ='white')
canvas.focus_set()

speedx = 0
speedy = 0
speed = 1

# Make variable to store after call object
after_obj = None

x1=40
y1=40

oval=canvas.create_oval(x1-10,y1-10,x1+10,y1+10,width=2,fill='orange')

def key_press(event):
    global x1, y1
    global speedx, speedy, speed
    global after_obj
    button = event.keysym
    if button == 'Up':
        speedx = 0
        speedy = -speed
    elif button == 'Down':
        speedx = 0
        speedy = speed
    elif button == 'Right':
        speedx = speed
        speedy = 0
    elif button == 'Left':
        speedx = -speed
        speedy = 0
    # Only call move from here if there is no after scheduled
    if after_obj is None:
        move()

def move():
    global x1,y1
    global oval
    global speedx, speedy
    global after_obj
    x1 += speedx
    y1 += speedy
    canvas.delete(oval)
    oval = canvas.create_oval(x1+10,y1-10,x1-10,y1+10,width=2,fill='orange')
    # Save the after call object
    after_obj = window.after(10, move)

def key_release(event):
    global speedx, speedy  
    global after_obj
    # When pressing multiple buttons at the same time you can get a key release without an after_obj, so check if it exists then cancel it
    if after_obj:
        window.after_cancel(after_obj)
    # Reset after_obj to None so move can be called from key_press again
    after_obj = None
    speedx = 0
    speedy = 0


canvas.bind('<KeyPress>', key_press)
canvas.bind("<KeyRelease>", key_release)
canvas.pack(padx =5, pady =5)
window.mainloop()