python - Tkinter Canvas 滚动条不跟随帧超过某个点

Question

我一直在努力理解二叉树的绘制。我在

http://billmill.org/pymag-trees/

所提供的代码使用的图形调用不属于我认识的任何 python 库，因此我已将图形调用转换为 tkinter 并让代码运行，除了一个意外行为。当我调整框架大小时(使其变大)，滚动条有时会​​被遗忘。在重新调整大小时，它们不会停留在框架上。这是代码:

from tkinter import *
from gen import Tree
from demo_trees import trees
from knuth import layout

r = 30
rh = r*1.5
rw = r*1.5

def drawt(canvas, root, depth):
    canvas.create_oval(root.x * rw, depth * rh, 
                   root.x * rw + r, depth * rh + r, 
                   fill = 'white',
                   width = 2)
    for child in root.children:
        drawt(canvas, child, depth+1)

def drawconn(canvas, root, depth):
    for child in root.children:
        canvas.create_line(root.x * rw + (r/2), depth * rh + (r/2),
         child.x * rw + (r/2), (depth+1) * rh + (r/2),
         width = 2)
        drawconn(canvas, child, depth+1)

def main():

    root = Tk()

    # Create the main frame. The frame will include a 
    # scrollable canvas.
    frame = Frame(root, width=500, height=309, relief=SUNKEN)
    frame.grid_rowconfigure(0, weight=1)
    frame.grid_columnconfigure(0, weight=1)

    # Add scroll bars
    xscrollbar = Scrollbar(frame, orient=HORIZONTAL)
    xscrollbar.grid(row=1, column=0, sticky=E+W)

    yscrollbar = Scrollbar(frame)
    yscrollbar.grid(row=0, column=1, sticky=N+S)

    # Add the canvas
    canvas = Canvas(frame, width=500, height=300,
                scrollregion=(-20, -20, 500, 300),
                xscrollcommand=xscrollbar.set,
                yscrollcommand=yscrollbar.set)

    canvas.grid(row=0, column=0, sticky=N+S+E+W)

    xscrollbar.config(command=canvas.xview)
    yscrollbar.config(command=canvas.yview)

    frame.pack()

    # Now draw the tree
    t = layout(trees[2])
    drawconn(canvas, t, 0)
    drawt(canvas, t, 0)

    root.mainloop()

if __name__ == '__main__':
    main()

绘图正在正确滚动并且在调整框架大小(更大)之前一切都很好谁能告诉我为什么滚动条不随框架移动？

如果有兴趣，完整的树绘制代码来自上面的链接，与提供的下载的figure2.py中的代码相对应。

Answer 1

很难确定，因为缺少依赖项我无法运行你的代码，但如果我不得不猜测，我会说这是因为你没有打包框架，这样它就会扩展和收缩.你说滚动条“落后了”，但我敢打赌 Canvas 也有同样的问题。

尝试修改打包框架的行:

frame.pack(side="top", fill="both", expand=True)