Animate the color of rectangle

Question

I want to change the color of rectangle after a certain period of time.

I tried root.after() method but it is not working.

    import time
    from tkinter import *

    def task():
      canvas= Canvas()
      canvas.create_rectangle(0,0,100,100,fill='red')
      canvas.pack()
      time.sleep(2)
      canvas.create_rectangle(0,0,100,100,fill='blue')
      canvas.pack()
      time.sleep(2)
      print("Testing...")


    root = Tk()
    canvas = Canvas(root)
    while(1):
      task()
      root.mainloop()

Given code running continuously and root windows get hang for certain time. Rectangle color should change after 2 seconds of delay.

task() will be executed only once because root.mainloop() will block the while loop. You should use after(). What have you tried using after()? — acw1668
I used after() in function as well as in main() function. root.mainloop() was wrong in my code. Thanks for your reply. — VipinSC

Saad Saad · Accepted Answer · 2019-04-24T07:09:45

Using time.sleep() hangs the window as well as while loop. To use time.sleep in tkinter we use after(ms) (ms-milliseconds) in the functions so the GUI won't hang.

While does the same, so we use after(ms, callback, args) function.

Here is an example of what you are trying to achieve. The rectangle will change his color every 1000ms (1 sec) from red to blue - blue to red so on. Also in your code you were creating a new canvas and rectangle every 4 secs. What I did is, I defined one canvas and one rectangle outside the task() function and gave the rectangle a tag (tag='rect') for the reference through which edit that one rectangle's color without creating unnecessary items. I hope this helped you.

Example:

from tkinter import *

root = Tk()
canvas = Canvas(root)
canvas.pack()
canvas.create_rectangle(0,0,100,100,fill='red', tag='rect')

def task():
    l = root.after(1000, task)

    if int(l.split('#')[1]) % 2 == 0:
        canvas.itemconfig('rect', fill='blue')
    else: 
        canvas.itemconfig('rect', fill='red')

task()

root.mainloop()

Animate the color of rectangle

1 Answers