Tkinter 无法识别按键

Question

我正在尝试编写一个程序，以便绘制一辆沿着屏幕移动的汽车，上下箭头键可以改变汽车的速度。但是，当我按下任一键时，都不会调用任何命令。我试过将 bind_all 和焦点线更改为 self.canvas 但这也没有用。我该如何解决这个问题？

class racingCar:
    def __init__(self):
        window = Tk()
        window.title("Racing Car")

        self.cWidth = 500
        self.cHeight = 200
        self.canvas = Canvas(window, width = self.cWidth, height = self.cHeight, bg = "white")
        self.canvas.pack()

        self.x = 0
        self.y = self.cHeight
        self.drawCar(self.x, self.y)

        self.dx = 5
        self.sleepTime = 50
        self.animate()

        window.bind_all("<Up>", self.increaseSpeed)
        window.bind_all("<Down>", self.decreaseSpeed)
        window.focus()

        window.mainloop()

    def drawCar(self, x, y):
        self.canvas.create_rectangle(x, y - 20, x + 50, y - 10, fill = "yellow", tags = "car")
        self.canvas.create_oval(x + 10, y - 10, x + 20, y, fill = "black", tags = "car")
        self.canvas.create_oval(x + 30, y - 10, x + 40, y, fill = "black", tags = "car")
        self.canvas.create_polygon([x + 10, y - 20, x + 20, y - 30, x + 30, y - 30, x + 40, y - 20], fill = "blue", tags = "car")

    def increaseSpeed(self, event):
        print("pressed up")
        self.dx += 2.5

    def decreaseSpeed(self, event):
        print("pressed down")
        if self.dx > 0:
            self.dx -= 2.5

    def animate(self):
        while not self.dx == 0:
            self.canvas.move("car", self.dx, 0)
            self.canvas.after(self.sleepTime)
            self.canvas.update()
            if self.x < self.cWidth + 10:
                self.x += self.dx
            else:
                self.x = -60
                self.canvas.delete("car")
                self.drawCar(self.x, self.y)
racingCar()

Answer 1

你不应该在同一个线程中使用 while 或 sleep tkinter 是运行 in.

在这种情况下，您使用 after() 的方式与 sleep 完全一样。

因为 tkinter 是单线程的，所以这些方法将阻塞主循环，并且在循环结束或睡眠结束之前不会发生任何其他事情。您的 canvas 被更新的原因是因为您在 while 循环中调用更新但您的事件仍然被阻止。

要解决此问题，请使用 after()，因为它适用于 tkinter 中的这种循环。

我已将您的代码更新为使用 after() 并对其进行了一些清理，以更严格地遵循 PEP8 风格指南。如果您有任何问题，请告诉我。

import tkinter as tk


class RacingCar(tk.Tk):
    def __init__(self):
        super().__init__()
        self.title("Racing Car")

        self.c_width = 500
        self.c_height = 200
        self.canvas = tk.Canvas(self, width=self.c_width, height=self.c_height, bg="white")
        self.canvas.pack()

        self.x = 0
        self.y = self.c_height
        self.draw_car(self.x, self.y)

        self.dx = 5
        self.after_time = 50
        self.animate()

        self.bind("<Up>", self.increase_speed)
        self.bind("<Down>", self.decrease_speed)

    def draw_car(self, x, y):
        self.canvas.create_rectangle(x, y - 20, x + 50, y - 10, fill="yellow", tags="car")
        self.canvas.create_oval(x + 10, y - 10, x + 20, y, fill="black", tags="car")
        self.canvas.create_oval(x + 30, y - 10, x + 40, y, fill="black", tags="car")
        self.canvas.create_polygon([x + 10, y - 20, x + 20, y - 30, x + 30, y - 30, x + 40, y - 20],
                                   fill="blue", tags="car")

    def increase_speed(self, _):
        print("pressed up")
        self.dx += 2.5

    def decrease_speed(self, _):
        print("pressed down")
        if self.dx > 0:
            self.dx -= 2.5

    def animate(self):
        if self.dx != 0:
            self.canvas.move("car", self.dx, 0)
            if self.x < self.c_width + 10:
                self.x += self.dx
            else:
                self.x = -60
                self.canvas.delete("car")
                self.draw_car(self.x, self.y)
            self.after(self.after_time, self.animate)


RacingCar().mainloop()

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