如何从 tkinter 的下拉菜单中提取信息？

Question

如何从某人在下拉菜单中选择的内容中获取信息？我希望下拉菜单影响计算器正在计算的内容。所以我想到的是检查他们选择的内容，然后使用 if 语句来确定要计算的内容。相关代码在底部，但请忽略value 和value1，因为它们只是测试。我想看看python会给我什么错误和信息。

import tkinter as tk
from tkinter import *
from PIL import ImageTk, Image

HEIGHT = 600
WIDTH = 900

h = 6.63e-34
c = 3.00e+8

def on_select(value):
    if value == OPTIONS[0]:
        label_enter_what['text'] = 'Enter wavelength in chosen unit below'
        label_unit['text'] = 'Enter what unit \n of wavelength'
        unit_set.set(OPTIONS_UNITS[1])
    elif value == OPTIONS[1]:
        label_enter_what['text'] = 'Enter wavelength in chosen unit below'
        label_unit['text'] = 'Enter what unit \n of wavelength'
        unit_set.set(OPTIONS_UNITS[1])
    elif value == OPTIONS[2]:
        label_enter_what['text'] = 'Enter energy in chosen unit below'
        label_unit['text'] = 'Enter what unit of energy'
        unit_set.set(OPTIONS_UNITS[3])


root = tk.Tk()

root.title("Photon property calculator")

canvas = tk.Canvas(root, height=HEIGHT, width=WIDTH)
canvas.pack()

background_image = ImageTk.PhotoImage(Image.open('interference.jpg'))
background_label = tk.Label(root, image=background_image)
background_label.place(relheight=1, relwidth=1)

frame = tk.Frame(root, bg='#3E3E3E', bd=5)
frame.place(relx=0.5, rely=0.1, relheight=0.1, relwidth=0.75, anchor='n')

entry_value = tk.Entry(frame, font=40, bg='white')
entry_value.place(relx=0.175, rely=0, relheight=1, relwidth=0.4)

frame_upper = tk.Frame(root, bg='#3E3E3E', bd=2.5)
frame_upper.place(relx=0.5, rely=0.03, relheight=0.06, relwidth=0.75, anchor='n')

label_what_to_calc = tk.Label(frame_upper, bg='white', text='Enter what \n to calculate')
label_what_to_calc.place(relx=0, rely=0, relheight=1, relwidth=0.15)

label_enter_what = tk.Label(frame_upper, bg='white', text='Select an option')
label_enter_what.place(relx=0.175, relheight=1, relwidth=0.4)

label_unit = tk.Label(frame_upper, bg='white', text='Enter what unit \n of wavelength')
label_unit.place(relx=0.6, relheight=1, relwidth=0.21)

lower_frame = tk.Frame(root, bg='#60A8FF', bd=10)
lower_frame.place(relx=0.5, rely=0.3, relheight=0.5, relwidth=0.75, anchor='n')

OPTIONS = [
    "Energy",
    "Frequency",
    "Wavelength"
]

value_var = tk.StringVar(value=OPTIONS[0])

drop = tk.OptionMenu(frame, value_var, *OPTIONS, command=on_select)
drop.place(relx=0, rely=0, relheight=1, relwidth=0.15)

OPTIONS_UNITS = ["μm",
                 "nm",
                 "pm",
                 "aJ",
                 "zJ",

]

unit_set = tk.StringVar(value=OPTIONS_UNITS[0])

drop_units = tk.OptionMenu(frame, unit_set, *OPTIONS_UNITS)
drop_units.place(relx=0.6, rely=0, relheight=1, relwidth=0.09)


def do_operation():
    first_number = entry_value.get()
    try:
        input = float(first_number)
        if value == [0] and value1 == [0]:
            new_num = input*10e-28
            label['text'] = str(h*c/new_num)
        elif OPTIONS ==[0] and OPTIONS_UNITS == [1]:
            label['text'] = str("test")
    except ValueError:
        print("wrong")


button = tk.Button(frame, text='Calculate!', font=40, bg="#F96612", fg='black', command=do_operation)
button.place(relx=0.7, relheight=1, relwidth=0.3)

label = tk.Label(lower_frame, bg='white', text='1')
label.place(relheight=1, relwidth=1)

root.mainloop()

Answer 1

如果你想在你的选项改变时运行一个函数，你可以在你的 StringVar() 对象上设置一个跟踪。 value_var.trace("w", on_select) 然后你可以使用value_var.get() 获取函数内部的值。我已在某种程度上将其编辑到您的代码中。我没有运行代码，所以它可能有一些问题；尽管已经解决了最常见的问题。如果您有任何问题，请随时发表评论。

import tkinter as tk
from tkinter import *
from PIL import ImageTk, Image

HEIGHT = 600
WIDTH = 900

h = 6.63e-34
c = 3.00e+8

value_var = tk.StringVar()  # value_var has to be moved ahead of your function

def on_select(*args):
    global value_var  # value_var has to be declared as a global in your function
    value = value_var.get()  # value_var.get() returns the current string.
    if value == OPTIONS[0]:
        label_enter_what['text'] = 'Enter wavelength in chosen unit below'
        label_unit['text'] = 'Enter what unit \n of wavelength'
        unit_set.set(OPTIONS_UNITS[1])
    elif value == OPTIONS[1]:
        label_enter_what['text'] = 'Enter wavelength in chosen unit below'
        label_unit['text'] = 'Enter what unit \n of wavelength'
        unit_set.set(OPTIONS_UNITS[1])
    elif value == OPTIONS[2]:
        label_enter_what['text'] = 'Enter energy in chosen unit below'
        label_unit['text'] = 'Enter what unit of energy'
        unit_set.set(OPTIONS_UNITS[3])


root = tk.Tk()

root.title("Photon property calculator")

canvas = tk.Canvas(root, height=HEIGHT, width=WIDTH)
canvas.pack()

background_image = ImageTk.PhotoImage(Image.open('interference.jpg'))
background_label = tk.Label(root, image=background_image)
background_label.place(relheight=1, relwidth=1)

frame = tk.Frame(root, bg='#3E3E3E', bd=5)
frame.place(relx=0.5, rely=0.1, relheight=0.1, relwidth=0.75, anchor='n')

entry_value = tk.Entry(frame, font=40, bg='white')
entry_value.place(relx=0.175, rely=0, relheight=1, relwidth=0.4)

frame_upper = tk.Frame(root, bg='#3E3E3E', bd=2.5)
frame_upper.place(relx=0.5, rely=0.03, relheight=0.06, relwidth=0.75, anchor='n')

label_what_to_calc = tk.Label(frame_upper, bg='white', text='Enter what \n to calculate')
label_what_to_calc.place(relx=0, rely=0, relheight=1, relwidth=0.15)

label_enter_what = tk.Label(frame_upper, bg='white', text='Select an option')
label_enter_what.place(relx=0.175, relheight=1, relwidth=0.4)

label_unit = tk.Label(frame_upper, bg='white', text='Enter what unit \n of wavelength')
label_unit.place(relx=0.6, relheight=1, relwidth=0.21)

lower_frame = tk.Frame(root, bg='#60A8FF', bd=10)
lower_frame.place(relx=0.5, rely=0.3, relheight=0.5, relwidth=0.75, anchor='n')

OPTIONS = [
    "Energy",
    "Frequency",
    "Wavelength"
]

value_var.trace("w", on_select)  # The "w" parameter sets it to trigger on write events

value_var.set(OPTIONS[0])  # value_var.set() will set the string value but it will also trigger the trace event.

drop = tk.OptionMenu(frame, value_var, *OPTIONS)
drop.place(relx=0, rely=0, relheight=1, relwidth=0.15)

OPTIONS_UNITS = ["μm",
                 "nm",
                 "pm",
                 "aJ",
                 "zJ",
]

unit_set = tk.StringVar(value=OPTIONS_UNITS[0])

drop_units = tk.OptionMenu(frame, unit_set, *OPTIONS_UNITS)
drop_units.place(relx=0.6, rely=0, relheight=1, relwidth=0.09)


def do_operation():
    first_number = entry_value.get()
    try:
        input = float(first_number)
        if value == [0] and value1 == [0]:
            new_num = input*10e-28
            label['text'] = str(h*c/new_num)
        elif OPTIONS ==[0] and OPTIONS_UNITS == [1]:
            label['text'] = str("test")
    except ValueError:
        print("wrong")


button = tk.Button(frame, text='Calculate!', font=40, bg="#F96612", fg='black', command=do_operation)
button.place(relx=0.7, relheight=1, relwidth=0.3)

label = tk.Label(lower_frame, bg='white', text='1')
label.place(relheight=1, relwidth=1)

root.mainloop()

没有跟踪和使用命令设置的回调。

import tkinter as tk
from tkinter import *
from PIL import ImageTk, Image

HEIGHT = 600
WIDTH = 900

h = 6.63e-34
c = 3.00e+8

value_var = tk.StringVar()  # value_var has to be moved ahead of your function

def on_select():
    global value_var  # value_var has to be declared as a global in your function
    value = value_var.get()  # value_var.get() returns the current string.
    if value == OPTIONS[0]:
        label_enter_what['text'] = 'Enter wavelength in chosen unit below'
        label_unit['text'] = 'Enter what unit \n of wavelength'
        unit_set.set(OPTIONS_UNITS[1])
    elif value == OPTIONS[1]:
        label_enter_what['text'] = 'Enter wavelength in chosen unit below'
        label_unit['text'] = 'Enter what unit \n of wavelength'
        unit_set.set(OPTIONS_UNITS[1])
    elif value == OPTIONS[2]:
        label_enter_what['text'] = 'Enter energy in chosen unit below'
        label_unit['text'] = 'Enter what unit of energy'
        unit_set.set(OPTIONS_UNITS[3])


root = tk.Tk()

root.title("Photon property calculator")

canvas = tk.Canvas(root, height=HEIGHT, width=WIDTH)
canvas.pack()

background_image = ImageTk.PhotoImage(Image.open('interference.jpg'))
background_label = tk.Label(root, image=background_image)
background_label.place(relheight=1, relwidth=1)

frame = tk.Frame(root, bg='#3E3E3E', bd=5)
frame.place(relx=0.5, rely=0.1, relheight=0.1, relwidth=0.75, anchor='n')

entry_value = tk.Entry(frame, font=40, bg='white')
entry_value.place(relx=0.175, rely=0, relheight=1, relwidth=0.4)

frame_upper = tk.Frame(root, bg='#3E3E3E', bd=2.5)
frame_upper.place(relx=0.5, rely=0.03, relheight=0.06, relwidth=0.75, anchor='n')

label_what_to_calc = tk.Label(frame_upper, bg='white', text='Enter what \n to calculate')
label_what_to_calc.place(relx=0, rely=0, relheight=1, relwidth=0.15)

label_enter_what = tk.Label(frame_upper, bg='white', text='Select an option')
label_enter_what.place(relx=0.175, relheight=1, relwidth=0.4)

label_unit = tk.Label(frame_upper, bg='white', text='Enter what unit \n of wavelength')
label_unit.place(relx=0.6, relheight=1, relwidth=0.21)

lower_frame = tk.Frame(root, bg='#60A8FF', bd=10)
lower_frame.place(relx=0.5, rely=0.3, relheight=0.5, relwidth=0.75, anchor='n')

OPTIONS = [
    "Energy",
    "Frequency",
    "Wavelength"
]


value_var.set(OPTIONS[0])  # value_var.set() will set the string value but will not trigger an event as the OptionMenu has not been created with the call back yet.

drop = tk.OptionMenu(frame, value_var, *OPTIONS, command=on_select)
drop.place(relx=0, rely=0, relheight=1, relwidth=0.15)

OPTIONS_UNITS = ["μm",
                 "nm",
                 "pm",
                 "aJ",
                 "zJ",
]

unit_set = tk.StringVar(value=OPTIONS_UNITS[0])

drop_units = tk.OptionMenu(frame, unit_set, *OPTIONS_UNITS)
drop_units.place(relx=0.6, rely=0, relheight=1, relwidth=0.09)


def do_operation():
    first_number = entry_value.get()
    try:
        input = float(first_number)
        if value == [0] and value1 == [0]:
            new_num = input*10e-28
            label['text'] = str(h*c/new_num)
        elif OPTIONS ==[0] and OPTIONS_UNITS == [1]:
            label['text'] = str("test")
    except ValueError:
        print("wrong")


button = tk.Button(frame, text='Calculate!', font=40, bg="#F96612", fg='black', command=do_operation)
button.place(relx=0.7, relheight=1, relwidth=0.3)

label = tk.Label(lower_frame, bg='white', text='1')
label.place(relheight=1, relwidth=1)

root.mainloop()