Tkinter画布不显示

Question

我正在尝试学习一些Python和Tkinter.下面的示例代码旨在在屏幕上放置两个窗口,一些按钮和一个带有图像的Canvas,并在其上绘制一些线条.

窗口和按钮看起来很好,但是我没有看到画布图像或画布线.我很感激帮助找出制作画布的必要条件.

from Tkinter import *
import Image, ImageTk

class App:

    def __init__(self, master):

    def scrollWheelClicked(event):
        print "Wheel wheeled"

    frame = Frame(master)
    frame.pack()
    self.button = Button(frame, text = "QUIT", fg="red", command=frame.quit)
    self.button.pack(side=LEFT)

    self.hi_there = Button(frame, text="Hello", command=self.say_hi)
    self.hi_there.pack(side=LEFT)

    top = Toplevel()
    canvas = Canvas(master=top, width=600, height=600)

    image = Image.open("c:\lena.jpg")
    photo = ImageTk.PhotoImage(image)
    item = canvas.create_image(0, 0, image=photo)

    canvas.create_line(0, 0, 200, 100)
    canvas.create_line(0, 100, 200, 0, fill="red", dash=(4, 4))
    canvas.create_rectangle(50, 25, 150, 75, fill="blue")

    canvas.pack

    testBtn = Button(top, text = "test button")
    testBtn.pack()

def say_hi(self):
    print "hi there everyone!"

root = Tk()
app = App(root)
root.mainloop()

Answer 1

我解决了这个问题:

self.photo = ImageTk.PhotoImage(image)
self.item = canvas.create_image(0, 0, image=self.photo)

必须在某处存储对ImageTk实例的引用,或者当您的App.__init__()方法返回时,它将被垃圾收集,并且画布将无法显示它.(Tkinter没有保留对图像的引用.)

保持对它的引用的一种方法是将其存储在"self.photo"或名为"photo"的变量中,或者像大多数程序员一样对常量变量(不变的变量,如'TEN = 10') ),'PHOTO = PhotoImage(...)'为什么......我不知道.导入模块'gc'(内置Python 3的垃圾收集模块)并运行gc.disable()不起作用.(如果你想尝试一下:https://docs.python.org/3/library/gc.html)