使用`after`时无法“闪烁” /更改tkinter小部件的颜色

Question

I'm trying to simulate a blink of a label widget by changing its color in this manner:

a) change to color #1, pause 1 sec,

b) change to color #2, pause 1 sec,

c) loop again using tk.after to rerun this procedure.

But the result is a constant color, #2.

self.blink_status is an index telling communication status is OK, and equals to 1 . of course code was tested with a constant value self.blink_status=1

def blink_tx(self):
    if self.blink_status == 1:
        self.tx_label["bg"] = 'green'
        self.tx_value.set('Tx')
        sleep(1)
        self.tx_label["bg"] = 'blue'
        sleep(1)
    elif self.blink_status == 0:
        self.tx_label["bg"] = 'red'
        self.tx_value.set('*')
        sleep(2)
        self.tx_label["bg"] = 'orange'
    else:
        self.tx_label["bg"] = 'red'
        self.tx_value.set('x')
        sleep(2)

    self.status_frame.after(3500, self.blink_tx)

the way self.tx_label and self.tx_value are defined :

self.tx_label = tk.Label(self.status_frame, textvariable=self.tx_value, relief=tk.GROOVE, width=2)
self.tx_label.grid(row=0, column=4, sticky=tk.E)

Answer 1

You cannot use sleep() inside of a tkinter instance. Tkinter is a single thread application and when you tell it to sleep everything in the event list is put on hold/freezes. You need to use after() for any delays in your code. The after() method is specifically meant to manage delays in tkinter.

Because in your example it appears you are running 2 separate delays my example will provide both delays.

Here is an exampled composed from the code you provided. We can set all the delays we need buy provided a 2nd function. I have added a random number generator to the code to illustrate a continuous change of the colors.

import tkinter as tk
import random


class MainApp(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)

        self.tx_value = tk.StringVar()
        self.tx_value.set("test")
        self.blink_status = 1

        self.tx_label = tk.Label(self, textvariable=self.tx_value, relief=tk.GROOVE, width=4, height=2)
        self.tx_label.grid(row=0, column=4, sticky=tk.E)
        self.blink_tx()

    def blink_tx_step_2(self, color=None):
        if color != None:
            self.tx_label["bg"] = color
        self.after(3500, self.blink_tx)

    def blink_tx(self):
        if self.blink_status == 1:
            self.tx_label["bg"] = 'green'
            self.tx_value.set('Tx')
            self.blink_status = random.randint(0, 2)
            self.after(1000, self.blink_tx_step_2, 'blue')
        elif self.blink_status == 0:
            self.tx_label["bg"] = 'red'
            self.tx_value.set('*')
            self.blink_status = random.randint(0, 2)
            self.after(2000, self.blink_tx_step_2, 'orange')
        else:
            self.tx_label["bg"] = 'red'
            self.tx_value.set('x')
            self.blink_status = random.randint(0, 2)
            self.after(2000, self.blink_tx_step_2)


if __name__ == '__main__':
    app = MainApp()
    app.mainloop()

Answer 2

time.sleep() is blocking your GUI updates; do not use it with a GUI. Use root.after instead.

The following label will start blinking when you click on the GUI:
You can adapt it to your own code that was not provided.

import tkinter as tk


class BlinkerLabel(tk.Label):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.status = 1

    def blink(self, event):
        if self.status == 1:
            self["bg"] = 'green'
        elif self.status == 0:
            self["bg"] = 'red'

        self.status = (self.status + 1) % 2
        self.after(3500, self.blink, 'dummy_event')  # <-- this creates the 'delay' between blinks


if __name__ == '__main__':

    root = tk.Tk()
    lbl = BlinkerLabel(root, text='I blink!')
    lbl.pack()

    root.bind('<Button-1>', lbl.blink)

    root.mainloop()

Answer 3

Thanks for @Mike-SMT and @Reblochon Masque for helping. TNX ALOT

My code fix:

def blink_tx(self):
    def blink_1(color1, color2, txt):
        self.tx_label["bg"] = color1
        self.tx_value.set(txt)
        self.after(t_blink, blink_2, color2)

    def blink_2(color):
        self.tx_label["bg"] = color
        self.after(t_blink, self.blink_tx)

    t_blink = 2500
    if self.blink_status == 1:
        blink_1('green', 'orange', 'Tx')
    elif self.blink_status == 0:
        blink_1('red', 'yellow', '*')
    else:
        blink_1('red', 'red', 'X')