Python - Tkinter - 标签未更新

Question

Any ideas why the leftresult_label label does not update? The function seems to work but the label does not update. I have looked everywhere and can't find an answer. The 'left' value gets set but the label does not change.

from tkinter import *

root = Tk(className="Page Calculator")

read = IntVar()

total = IntVar()

left = IntVar()

read.set(1)

total.set(1)

left.set(1)

read_label = Label(root,text="Pages Read:")
read_label.grid(column=1, row=1)

total_label = Label(root,text="Total Pages:")
total_label.grid(column=1, row=2)

read_entry = Entry(root,textvariable=read)
read_entry.grid(column=2, row=1)

total_entry = Entry(root,textvariable=total)
total_entry.grid(column=2, row=2)

def func1():
    left.set(total.get() - read.get())
    print(left.get())

calculate_button = Button(root,text="Calculate",command= func1)
calculate_button.grid(column=2, row=3)

percenet_label = Label(root,text="Percent Finished:")
percenet_label.grid(column=1, row=4)

left_label = Label(root,text="Pages Left:")
left_label.grid(column=1, row=5)

percenetresult_label = Label(root,text=left.get())
percenetresult_label.grid(column=2, row=4)

leftresult_label = Label(root,text="")
leftresult_label.grid(column=2, row=5)

root.mainloop()

Answer 1

To make the function do the job, you'd rather have your label:

leftresult_label = Label(root, textvariable=left)

Once it's tkinter class variable, tkinter takes care about when you change the value. Once you click the button,

def func1():
    left.set(total.get() - read.get())
    percent.set(int(read.get()*100/total.get()))

left and percent values, which are instances of tkinter.IntVar() class have immidiate effect on widgets (labels in this case) where those values are set as textvariable, just as you have it at Entry widgets.

Here is full code:

from tkinter import *

root = Tk(className="Page Calculator")
read = IntVar()
total = IntVar()
left = IntVar()
percent = IntVar()

read.set(1)
total.set(1)
left.set(1)
percent.set(1)

def func1():
    left.set(total.get() - read.get())
    percent.set(int(read.get()*100/total.get()))

read_label = Label(root,text="Pages Read:")
read_label.grid(column=1, row=1)

read_entry = Entry(root,textvariable=read)
read_entry.grid(column=2, row=1)

total_label = Label(root,text="Total Pages:")
total_label.grid(column=1, row=2)

total_entry = Entry(root,textvariable=total)
total_entry.grid(column=2, row=2)


calculate_button = Button(root,text="Calculate",command= func1)
calculate_button.grid(column=2, row=3)

percenet_label = Label(root,text="Percent Finished:")
percenet_label.grid(column=1, row=4)

left_label = Label(root,text="Pages Left:")
left_label.grid(column=1, row=5)

percenetresult_label = Label(root,textvariable=percent)
percenetresult_label.grid(column=2, row=4)

leftresult_label = Label(root,textvariable=left)
leftresult_label.grid(column=2, row=5)

root.mainloop()

Answer 2

code including progress bar. update_idletasks() used to keep label and progress bar running.

from tkinter import *
from tkinter import ttk
root = Tk()
root.title('Counter Test')
root.iconbitmap('IT.ico')
root.geometry("800x400")

def missing():
    while i < 100:                        
        progress1['value'] = i 
        label1.config(text=progress1['value'])
        root.update_idletasks()
        i += 1
        
progress1 = ttk.Progressbar(root, orient=HORIZONTAL, length=250, mode='determinate')
progress1.pack(pady=15)

label1 = Label(root, text="")
label1.pack(pady=15)

button_1 = Button(root, text="Missing", command=missing)
button_1.pack(pady=15)

button_q = Button(root, text="Quit", command=root.destroy)
button_q.pack(pady=15)

root.mainloop() 

Answer 3

so to update controls immediately, like updating labels and TreeView elements this code worked for me.

window = tk.Tk()

window.update_idletasks()