tkinter OptionMenu 问题（bug？）：GUI 和程序值未保持同步（python 3.x）

在某些情况下（下面的演示），OpenMenu 小部件上显示的值与程序使用的值不匹配，这会导致当用户期望选项 A 时执行选项 B - 导致 WTF？用户的反应。

不幸的是，OptionMenu 小部件没有我与其他小部件一起使用来轻松处理问题的“命令”选项（例如演示中的“A_Button”小部件）。我尝试过使用绑定，但到目前为止我还没有解决问题的“灵丹妙药”。

我检查了常用的地方（NMT、effbot、这里等），发现这个小部件几乎没有有用的文档，特别是在处理下拉列表中的项目时。 （知道如何确定列表中的项目数，列表中当前选定值的位置/索引以及如何将小部件包含在 GUI 的选项卡序列中将会很有用）。

我的申请是多语言的；当语言改变显示值时andOptionMenu 小部件的下拉列表必须相应更改。 （顺便说一句，多语言意味着您不能在代码中直接使用 .get() 的结果，特别是在添加另一种语言的情况下。为了获得语言独立性，我使用通过将 .get() 值与值匹配而创建的索引在选项菜单中 - 有更好的方法吗？）

在演示代码中，所选语言决定 OptionMenu 小部件显示的值。 “使用日期”（按钮小部件）正是实际应用程序的启动方式（以及为什么强制 GUI 和程序值始终匹配 - 这并不总是发生）。相比之下，“今天是什么日子？” （也是一个按钮小部件）使用命令选项来实现预期/正确的行为 - 正如我的应用程序中多次成功完成的那样。

要查看问题，请运行演示，选择任意语言。在不改变语言的情况下，日子会多次改变。请注意，打印值（由我的应用程序使用）始终是 GUI 小部件上显示的值后面的一个选择。接下来，在不更改日期的情况下，选择不同的语言（将打印新语言）。 OptionMenu 下拉值不会更改，直到after鼠标离开 OptionMenu 小部件 - 及其显示的值never被“翻译”成新语言。

我忽略/遗漏/做错了什么？

from tkinter import Button, IntVar, Label, OptionMenu, Radiobutton, Tk, StringVar
#    You can skip over this section, it's basic gruntwork needed to set up the demo (values used have no impact on the problem).
English    = 0    
French     = 1
Spanish    = 2
DayNumbers = 3
DefaultDay = 2              # Corresponds to Tuesday, emulates the user's choice of day (on the GUI)
DefaultLanguage = English
Languages  = [ "English", "French", "Spanish", "Day Numbers" ] # for use on GUI
EnglishWeekdays  = [ "Sunday",   "Monday", "Tuesday", "Wednesday", "Thursday", "Friday",   "Saturday" ]
FrenchWeekdays   = [ "dimanche", "lundi",  "mardi",   "mecredi",   "jeudi",    "vendredi", "samedi"   ]
SpanishWeekdays  = [ "domingo",  "lunes",  "martes",  "miercoles", "jeuves",   "viernes",  "sabado"   ]
NumberedWeekdays = [ "Day 0",    "Day 1",  "Day 2",   "Day 3",     "Day 4",    "Day 5",    "Day 6"    ]
DayNames = [ EnglishWeekdays, FrenchWeekdays, SpanishWeekdays, NumberedWeekdays ]
#   The variables
LanguageInUse = DefaultLanguage
Weekdays      = DayNames[ LanguageInUse ]
Today         = DefaultDay  # Isolates application code from language on GUI
#-------------------------------------------------------------------------------
def ChooseLanguage( ParentFrame ) :   
    global LanguageInUse, DropdownMenu
    GUI_Language = IntVar( value = LanguageInUse )   
    #---------------------------------------------------------------------------
    def SwitchLanguage():        
        global LanguageInUse , Weekdays       
        LanguageInUse = GUI_Language.get()   
        print( "SwitchLanguage sets language index to", LanguageInUse, "(" + Languages[ LanguageInUse ] + ")"  )             
        Weekdays = DayNames[ LanguageInUse ]
        DropdownMenu[ 'menu' ][ 'title' ] =  Weekdays[ Today ]         
        for i, DayName in enumerate( Weekdays ) :
            DropdownMenu[ 'menu' ].entryconfig( i )['label' ] = DayName
        return           
    #---------------------------------------------------------------------------
    LanguageButton = []
    for LanguageIndex, Language in enumerate( Languages ) :   
        LanguageButton = LanguageButton + [ Radiobutton( ParentFrame, 
                    indicatoron = False, width = 12, 
                    variable = GUI_Language, command = lambda: SwitchLanguage(),
                    text = Language, value = LanguageIndex ) ]
        LanguageButton[ LanguageIndex ].grid( row = 0 , column = LanguageIndex )    
    return
#-------------------------------------------------------------------------------
def GetDayIndex() :    
    global Today, DropdownMenu
    Today = 0    
    for Index, DayName in enumerate( Weekdays ) :
        if ( GUI_Value.get() == DayName ) :
            Today = Index
            break
    print( "GetDayIndex sets weekday index to", Today, "(" + Weekdays[ Today ] + ")" )

    for i, j in enumerate( Weekdays ) :
        DropdownMenu[ 'menu' ].entryconfig( i , label = j )
    return
#-------------------------------------------------------------------------------
def DoSomethingUseful() :
    print( "   Program uses " +  str( Today ) + " (" +  Weekdays[ Today ]  +")" )
    return
#-------------------------------------------------------------------------------
# The mainline
root = Tk() 
GUI_Value = StringVar( value = Weekdays[ Today ] )
Widget1 = Label( root, text = "Today is" )
Widget1.grid( row = 1, column = 0 )

DropdownMenu = OptionMenu(  root, GUI_Value, *DayNames[ LanguageInUse ] )    # NOT in TAB key sequence !!!
DropdownMenu.grid( row = 1, column = 1  )

DropdownMenu.bind( "<Leave>", lambda _ : GetDayIndex() )

#OptionMenu_Configuration( DropdownMenu )
A_Button = Button( root, text = "What day is it??", command = lambda : GetDayIndex() )
B_Button = Button( root, text = "Use the date",  command = lambda: DoSomethingUseful() )
A_Button.grid( row = 1, column = 2 )
B_Button.grid( row = 1, column = 3 )
ChooseLanguage( root )  # creates/manages the language choice widgets

root.mainloop()

你的程序的逻辑对我来说不太清楚，尤其是'<Leave>'具有约束力，但让我们尝试一般性地回答您的问题：

1. Unfortunately the OptionMenu widget does not have the "command" option that I've used with other widgets to easily handle the problem (e.g. "A_Button" widget in demo).

你错了，因为它有这个option https://www.tcl.tk/man/tcl/TkCmd/menu.htm#M55:

import tkinter as tk


def dropdown_callback(selected=None):
    print('Currently selected value is:\t%s' % selected)

root = tk.Tk()
str_var = tk.StringVar()
dropdown_menu = tk.OptionMenu(root, str_var, *['foo', 'bar', 'baz'], command=dropdown_callback)
dropdown_menu.pack()

root.mainloop()

另外，您还可以指定一个单独的command对于您的每个条目（很少有用）：

import tkinter as tk


def dropdown_callback(event=None):
    print('Currently selected value is:\t%s' % event)


def dropdown_callback_foo():
    print('Called callback is:\t%s' % dropdown_callback_foo.__name__)


def dropdown_callback_bar():
    print('Called callback is:\t%s' % dropdown_callback_bar.__name__)


root = tk.Tk()
str_var = tk.StringVar()
dropdown_menu = tk.OptionMenu(root, str_var, *['foo', 'bar', 'baz'], command=dropdown_callback)
dropdown_menu._OptionMenu__menu.entryconfig(0, command=dropdown_callback_foo)
dropdown_menu._OptionMenu__menu.entryconfig(1, command=dropdown_callback_bar)
dropdown_menu.pack()

root.mainloop()

2. ...the position/index of the currently selected value in the list...

再说一次，有一个option https://www.tcl.tk/man/tcl/TkCmd/menu.htm#M39为了那个原因：

import tkinter as tk


def dropdown_callback(selected=None):
    selected_index = root.tk.call(dropdown_menu.menuname, 'index', selected)
    print('Currently selected value is:\t%s\t\ton position:\t%d' % (selected, selected_index))

root = tk.Tk()
str_var = tk.StringVar()
dropdown_menu = tk.OptionMenu(root, str_var, *['foo', 'bar', 'baz'], command=dropdown_callback)
dropdown_menu.pack()

root.mainloop()

3. ...determine the number of items in the list...

这也是可以实现的，因为项目数只是最后一个索引 + 1：

import tkinter as tk


def dropdown_callback(selected=None):
    selected_index = root.tk.call(dropdown_menu.menuname, 'index', selected)
    total_count = root.tk.call(dropdown_menu.menuname, 'index', 'end') + 1
    print('Currently selected value is:\t%s\t\ton position:\t%d\t\twith total count:\t%d' 
          % (selected, selected_index, total_count))

root = tk.Tk()
str_var = tk.StringVar()
dropdown_menu = tk.OptionMenu(root, str_var, *['foo', 'bar', 'baz'], command=dropdown_callback)
dropdown_menu.pack()

root.mainloop()

从这一点来看，我认为，现在你的困惑OptionMenu都解决了。当然，堆叠顺序除外，但您可以更换您的OptionMenu with ttk.Combobox随时。没有这样的<Tab>, 行为Menu小部件，因为它们对命令的反应不同，例如lift。当然，这也是可以实现的，但这是另一个问题，因为有越来越多的“假设”！

就这样！