Tkinter和绑定到ListboxSelect事件的两个列表框的意外行为 [英] Unexpected behavior with Tkinter and two Listboxes bound to ListboxSelect event

问题描述

我正在处理的脚本中遇到一个异常问题.该程序是用Python3/Tkinter编写的.它初始化两个包装在两个单独框架中的列表框，并根据用户的命令显示一个或另一个.当用户在第一个列表框中选择一个项目，然后决定更改屏幕并在第二个框架中选择一个项目时，就会出现异常.

I’ve encountered an unusual problem in a script that I’m working on. The program is written in Python3/Tkinter. It initializes two Listboxes, wrapped in two separate Frames, and according to the user’s commands displays either one or the other. An exception arises when the user selects on one of the items in the first Listbox, then decides to change screen and selects an item in the second frame.

我创建了一个示例代码(如下)，以重复该问题.使用此代码，在运行时，单击第一个列表框(白色背景)中的一个项目将使第二个列表框出现(橙色背景).同样，第一个对象是未包装的"，因此用户将不再能够与其进行交互.最后，单击第二个列表框中的项目，会从第一个对象的"on_select_1"方法中引发IndexError.为什么在该事件之后执行该方法?我很清楚自己作为程序员的局限性，但是我很确定这不是应该发生的事情.

I’ve created a sample code (below), to replicate the problem. With this code, during runtime, clicking on one item in the first Listbox (white background) makes the second Listbox appear (orange background). Also, the first object is "unpacked" and thus the user should no longer be able to interact with it. Finally, clicking on an item in the second Listbox, raises an IndexError in the "on_select_1" method from the first object. Why would that method execute after that event?? I’m well aware of my limits as a programmer, but I’m pretty sure this is not what is supposed to happen.

import tkinter as tk


class Listbox1(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)
        self.lb1 = tk.Listbox(self)
        for i in ["item 1.1", "item 1.2", "item 1.3", "item 1.4"]:
            self.lb1.insert(tk.END, i)
        self.lb1.bind("<<ListboxSelect>>", self.on_select_1)
        self.lb1.pack()

    def on_select_1(self, *args):
        try:
            print("item {} selected in listbox 1".format(self.lb1.curselection()[0]))
        except IndexError:
            print("IndexError raised in method 'on_select_1'")

        self.master.switch()


class Listbox2(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)
        self.lb2 = tk.Listbox(self, bg='orange')
        for i in ["item 2.1", "item 2.2", "item 2.3", "item 2.4"]:
            self.lb2.insert(tk.END, i)
        self.lb2.bind("<<ListboxSelect>>", self.on_select_2)
        self.lb2.pack()

    def on_select_2(self, *args):
        print("item {} selected in listbox 2".format(self.lb2.curselection()[0]))


class App(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)
        self.pack()
        self.lb1_frame = Listbox1(self)
        self.lb2_frame = Listbox2(self)
        self.lb1_frame.pack()

    def switch(self):
        self.lb1_frame.pack_forget()
        self.lb2_frame.pack()


def main():
    root = tk.Tk()
    app = App(root)
    app.mainloop()


if __name__ == '__main__':
    main()

推荐答案

默认情况下，tkinter仅允许一个小部件同时保留选择.因此，当您在第二个列表框中选择某项时，将取消选择在第一个列表框中选择的项目.这将导致您的函数被调用.发生这种情况时，self.lb1.curselection()[0])会引发错误，因为选择为空.

By default, tkinter only allows one widget to hold the selection at a time. Thus, when you select something in your second listbox, the item selected in the first listbox is deselected. That causes your function to be called. When this happens, self.lb1.curselection()[0]) throws an error because the selection is empty.

一个简单的解决方案是在两个列表框中都将exportselection选项设置为False.当您在第二个列表框中选择某些内容时，该选择在第一个列表框中保持不变.

A simple solution that allows the selection to remain unchanged in the first listbox when you select something in the second listbox is to set the exportselection option to False for both listboxes.

self.lb1 = tk.Listbox(self, exportselection=False)
...
self.lb2 = tk.Listbox(self, bg='orange', exportselection=False)

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