I'd like to write a code that moves the red ball up and down on the canvas with python, but with the code below, the ball goes through the upper wall and disappears from the screen.What should I change?I want to make it using the winfo_height function.

I've tried many things and found out that

line19:if self.position[3]>=self.canvas_height:

There is something wrong with
I changed self.canvas_height to 500 and it worked, but it's out of line with what I really want to do.

I just want to use winfo_height to solve this problem.
Another thing we know is that if you print self.canvas_height, you get 1.Why does it say 1 instead of 500?

Q1. How do I move the red ball up and down?
Q2. Why print self.canvas_height to get 1?Why does Canvas already write height=500 so it becomes 1?

If Q2 can be solved, I think Q1 can be solved.Thank you for your understanding.

import tkinter
import time

Class Ball:
    def__init__(self, canvas, color):
        self.canvas=canvas
        self.id=self.canvas.create_oval (10, 10, 25, 25, fill=color)
        self.canvas.move (self.id, 250, 150)
        self.canvas_height=self.canvas.winfo_height()
        self.x = 0
        self.y = 1
        print(self.canvas_height)
    
    def draw(self):
        self.canvas.move (self.id, self.x, self.y)
        self.position = self.canvas.coords (self.id)
        if self.position[1]<=0:
            self.y = 1
        if self.position[3]>=self.canvas_height:
            self.y=-1
        


root=tkinter.Tk()
root.minsize (width=500, height=500)
root.resizable(0,0)
canvas=tkinter.Canvas (width=500, height=500)
canvas.place(x=0,y=0)

ball = Ball (canvas, "red")
while True:
    ball.draw()
    canvas.update()
    time.sleep(0.01)

root.mainloop()

python

2022-09-30 21:48

1 Answers

You must run self.canvas.update() immediately before self.canvas_height=self.canvas.winfo_height() (widget geometry configuration is performed to determine properties such as height).

As metropolis commented, when self.canvas_height=self.canvas.winfo_height() was inserted just before self.canvas.update(), the red ball now reflects up and down the window.

import tkinter
import time

Class Ball:
    def__init__(self, canvas, color):
        self.canvas=canvas
        self.id=self.canvas.create_oval (10, 10, 25, 25, fill=color)
        self.canvas.move (self.id, 250, 150)
        self.canvas.update() 
        self.canvas_height=self.canvas.winfo_height()
        self.x = 0
        self.y = 1
        print(self.canvas_height)
    
    def draw(self):
        self.canvas.move (self.id, self.x, self.y)
        self.position = self.canvas.coords (self.id)
        if self.position[1]<=0:
            self.y = 1
        if self.position[3]>=self.canvas_height:
            self.y=-1

root=tkinter.Tk()
root.minsize (width=500, height=500)
root.resizable(0,0)
canvas=tkinter.Canvas (width=500, height=500)
canvas.place(x=0,y=0)

ball = Ball (canvas, "red")
while True:
    ball.draw()
    canvas.update()
    time.sleep(0.01)

root.mainloop()

2022-09-30 21:48

If you have any answers or tips

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