python - 如何定期更改 tkinter 图像？

Question

我有一个保存在文件 test.bmp 中的图像，这个文件每秒被覆盖 2 次
(我想每秒显示 2 张图像)。

这是我目前所拥有的:

import tkinter as tk
from PIL import Image, ImageTk

root = tk.Tk()
img_path = 'test.bmp'
img = ImageTk.PhotoImage(Image.open(img_path), Image.ANTIALIAS))

canvas = tk.Canvas(root, height=400, width=400)
canvas.create_image(200, 200, image=img)
canvas.pack()

root.mainloop()

但我不知道如何每 ½ 秒刷新一次图像？
我正在使用 Python3 和 Tkinter。

Answer 1

哎呀，你问题中的代码看起来很familiar ...

由于需要通过一些神秘的未指定进程更新图像文件，因此想出一个由经过测试的代码组成的答案很复杂。这是在下面的代码中通过创建一个单独的线程来完成的，该线程独立于主进程定期覆盖图像文件。我试图用注释将这段代码与其余代码区分开来，因为我觉得它有点分散注意力，让事情看起来比实际情况更复杂。

主要内容是您需要使用通用的 tkinter 小部件 after()安排图像在未来某个时间刷新的方法。还需要注意首先创建一个占位 Canvas 图像对象，以便稍后可以就地更新它。这是必需的，因为可能存在其他 Canvas 对象，否则如果未创建占位符，更新的图像可能会根据相对位置覆盖它们(因此返回的图像对象 ID 可以保存并稍后用于更改它)。

from PIL import Image, ImageTk
import tkinter as tk

#------------------------------------------------------------------------------
# Code to simulate background process periodically updating the image file.
# Note: 
#   It's important that this code *not* interact directly with tkinter 
#   stuff in the main process since it doesn't support multi-threading.
import itertools
import os
import shutil
import threading
import time

def update_image_file(dst):
    """ Overwrite (or create) destination file by copying successive image 
        files to the destination path. Runs indefinitely. 
    """
    TEST_IMAGES = 'test_image1.png', 'test_image2.png', 'test_image3.png'

    for src in itertools.cycle(TEST_IMAGES):
        shutil.copy(src, dst)
        time.sleep(.5)  # pause between updates
#------------------------------------------------------------------------------

def refresh_image(canvas, img, image_path, image_id):
    try:
        pil_img = Image.open(image_path).resize((400,400), Image.ANTIALIAS)
        img = ImageTk.PhotoImage(pil_img)
        canvas.itemconfigure(image_id, image=img)
    except IOError:  # missing or corrupt image file
        img = None
    # repeat every half sec
    canvas.after(500, refresh_image, canvas, img, image_path, image_id)  

root = tk.Tk()
image_path = 'test.png'

#------------------------------------------------------------------------------
# More code to simulate background process periodically updating the image file.
th = threading.Thread(target=update_image_file, args=(image_path,))
th.daemon = True  # terminates whenever main thread does
th.start()
while not os.path.exists(image_path):  # let it run until image file exists
    time.sleep(.1)
#------------------------------------------------------------------------------

canvas = tk.Canvas(root, height=400, width=400)
img = None  # initially only need a canvas image place-holder
image_id = canvas.create_image(200, 200, image=img)
canvas.pack()

refresh_image(canvas, img, image_path, image_id)
root.mainloop()