tkinter Checkbutton 小部件返回错误的布尔值 [英] tkinter Checkbutton widget returning wrong boolean value

问题描述

我这里有一个简单的 GUI，它假设根据检查按钮是否被选中来返回一个布尔值.我已将布尔变量设置为 False 因此空检查按钮.我不明白的是，当我检查按钮时，绑定到该小部件的函数返回 False 而不是 True.这是为什么?

I have a simple GUI here that's suppose to return a boolean value depending on whether the check button is checked or not. I've set the boolean variable to False hence the empty check button. What I don't understand is that when I check the button, the function binded to that widget returns a False instead of True. Why is that?

这是代码...

from tkinter import *
from tkinter import ttk

def getBool(event):
    print(boolvar.get())

root = Tk()

boolvar = BooleanVar()
boolvar.set(False)

cb = Checkbutton(root, text = "Check Me", variable = boolvar)
cb.bind("<Button-1>", getBool)
cb.pack()

root.mainloop()

当检查空按钮时，函数输出...

when checking the empty button the function outputs...

False

既然选中了按钮，它不应该返回 True 吗?

Shouldn't it return True now that the button is checked?

推荐答案

在进行绑定回调后更改布尔值.举个例子，看看这个:

The boolean value is changed after the bind callback is made. To give you an example, check this out:

from tkinter import *

def getBool(event):
    print(boolvar.get())


root = Tk()

boolvar = BooleanVar()
boolvar.set(False)
boolvar.trace('w', lambda *_: print("The value was changed"))

cb = Checkbutton(root, text = "Check Me", variable = boolvar)
cb.bind("<Button-1>", getBool)
cb.pack()

root.mainloop()

当你按下 Checkbutton 时，第一个输出是 False 然后是 "The value was changed"，这意味着在 getBool 之后值被改变了 回调完成.

When you presses the Checkbutton, the first output is False then it's "The value was changed", which means that the value was changed after the getBool callback is completed.

你应该做的是使用 command 参数来设置回调，看:

What you should do is to use the command argument for the setting the callback, look:

from tkinter import *

def getBool(): # get rid of the event argument
    print(boolvar.get())


root = Tk()

boolvar = BooleanVar()
boolvar.set(False)
boolvar.trace('w', lambda *_: print("The value was changed"))

cb = Checkbutton(root, text = "Check Me", variable = boolvar, command = getBool)
cb.pack()

root.mainloop()

输出首先是值已更改"，然后是True.

在我的例子中，我使用了 boolvar.trace，它在布尔值改变时运行 lambda 回调 ('w')

For my examples, I used boolvar.trace, it runs the lambda callback when the boolean value changes ('w')

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