从tkinter OptionMenu获取值

Question

1我从OptionMenu选择值。

2点击按钮

但是回调函数parse打印了OptionMenu的默认值。我做错了什么？

我的代码

from tkinter import *
from functools import partial


def parse(shop, city):
    print(f"Parse {city} {shop}") # prints "all shops" but i expected "magnit" because i chosed it


master = Tk()

variable_shop = StringVar(master)
variable_shop.set("all shops") # default value

w = OptionMenu(master, variable_shop, "all shops", "5ka", "magnit", "three").pack()

variable_city = StringVar(master)
variable_city.set("all cities") # default value
w2 = OptionMenu(master, variable_city, "all cities", "Moscow", "Saint Petersburg").pack()

callback = partial(parse, variable_shop.get(), variable_city.get())
b1 = Button(text="Run with values from OptionMenu", command=callback).pack()

mainloop()

Answer 1

您的回调行在程序启动时运行，因此它在引导时保存值。当用户单击按钮时，您需要将那些get()调用移动到稍后运行的某个地方。将它们放入解析函数中是有意义的，同时也消除了对分部的需要。

from tkinter import *

def parse():
    city = variable_city.get()
    shop = variable_shop.get()
    print(f"Parse {city} {shop}") 

master = Tk()

variable_shop = StringVar(master)
variable_shop.set("all shops") # default value

OptionMenu(master, variable_shop, "all shops", "5ka", "magnit", "three").pack()

variable_city = StringVar(master)
variable_city.set("all cities") # default value
OptionMenu(master, variable_city, "all cities", "Moscow", "Saint Petersburg").pack()

Button(text="Run with values from OptionMenu", command=parse).pack()

mainloop()

Answer 2

考虑这一行代码：

callback = partial(parse, variable_shop.get(), variable_city.get())

它在功能上与此相同：

shop = variable_shop.get()
city = variable_city.get()
callback = partial(parse, shop, city)

换句话说，您在创建get方法之后调用它大约一毫秒，而不是等到用户单击该按钮后再调用它。

您根本不需要使用partial。只需让回调调用一个常规函数，并让该函数检索值。这将使代码更易于编写、更易于理解和更易于调试。

def parse():
    shop = variable_shop.get()
    city = variable_city.get()
    print(f"Parse {city} {shop}") 
...
b1 = Button(text="Run with values from OptionMenu", command=parse)
b1.pack()