tkinter (python): assign class method to a key

问题:

In my simple code, a red ball is falling down in a straight line (that's working). When I push the right arrow key, I want the ball to also move in right direction. This is not working, however. What am I doing wrong?

from tkinter import *

root = Tk()

canvas = Canvas(root, height=400, width=500, background='black')
canvas.pack()


class Bird:
    def __init__(self, canvas, coords):
        self.canvas = canvas
        self.coords = coords
        self.bird = canvas.create_rectangle(coords, fill='red')

    def gravity(self):
        self.canvas.move(self.bird, 0, 10)
        self.canvas.after(200, self.gravity)

    def moveRight(self, event):
        self.canvas.move(self.bird, 10, 0)
        self.canvas.after(200, self.moveRight)

bird = Bird(canvas, (100, 100, 110, 110))

bird.gravity()

canvas.bind('<Right>', bird.moveRight)

root.mainloop()

I have another additional question:

Is it possible to call this "after"-function or a similar function for the whole canvas instead of the two methods separately?

If you see any other flaws with my code plz let me know!

Thanks!

回答1:

You must bind the right key to the canvas inside the class, and set the focus on the canvas:

from tkinter import *

root = Tk()

canvas = Canvas(root, height=400, width=500, background='black')
canvas.pack()


class Bird:
    def __init__(self, canvas, coords):
        self.canvas = canvas
        self.coords = coords
        self.bird = canvas.create_rectangle(coords, fill='red')
        self.canvas.bind('<Right>', self.moveRight)
        self.canvas.focus_set()

    def gravity(self):
        self.canvas.move(self.bird, 0, 10)
        self.canvas.after(200, self.gravity)

    def moveRight(self, event=None):
        self.canvas.move(self.bird, 10, 0)
        self.canvas.after(200, self.moveRight)


bird = Bird(canvas, (100, 100, 110, 110))

bird.gravity()

root.mainloop()

回答2:

The problem you are facing is that you are binding keyboard events, but the events can only work if the widget with the bindings has the keyboard focus. You can give the canvas the keyboard focus with focus_set():

canvas = Canvas(root, height=400, width=500, background='black')
canvas.focus_set()

Is it possible to call this "after"-function or a similar function for the whole canvas instead of the two methods separately?

Yes. Your binding can call any function you want. If you expect to have more than one object and you want them all to move at the same time, you can move them all from a function.

First, remove the call to after from moveRight. Next, define a global function that calls moveRight for every object. For example:

def move_them_all():
    bird1.moveRight()
    bird2.moveRight()
    something_else.moveRight()
    self.canvas.after(1000, move_them_all)
...
canvas = Canvas(root, height=400, width=500, background='black')
...
canvas.bind('<right>', move_them_all)