python - Why ttk Progressbar appears after process in Tkinter

5
votes

I want to create a large text upon Tkinter menu command and provide visual support by a progress bar. Although the progress bar is meant to start before the subsequent time-consuming loop, the progress bar shows up only after the large text was created and displayed.

def menu_bar(self):
    self.create_menu.add_command(label="Create large file", 
    command=self.create_large_file)

def create_large_file(self):
    self.progressbar = ttk.Progressbar(self.master, mode='indeterminate')
    self.progressbar.pack()
    self.progressbar.start()
    self.text.delete(1.0, 'end')
    self.file_content = []

i = 0
while i < 2000000:
    line = lfd.input_string
    self.file_content.append(line + "\n")
    i += 1

self.file_content = ''.join(self.file_content)
self.text.insert(1.0, self.file_content)
2
pythonprogress-barttk
The default update interval for a mode='indeterminate' progressbar is 50ms, so maybe your loop isn't all that time-consuming. Try specifying a smaller time value argument when you call its start() method. – martineau
That doesn't seem to help. I specified a smaller time value as update interval and I increased the process. I wait approx. 3 seconds while the loop is being processes, only after that the process bar appears. – solarisman

2 Answers

7
votes

I think the problem is that the time-consuming loop is preventing the tkinter event loop, mainloop(), from running. In other words, when your work intensive function runs in the same thread as the GUI, it interferes with it by hogging the interpreter.

To prevent this you can use a secondary Thread to run your function and run the GUI and its progressbar in the main thread. To give you an idea of how to do this, here's a simple example I derived from code in another (unrelated) progressbar question to show how easily something like that can be done. Note: It's generally recommended that secondary threads not be given direct access to the main thread's tkinter objects.

from Tkinter import *
import ttk

import time
import threading

def foo():
    time.sleep(5) # simulate some work

def start_foo_thread(event):
    global foo_thread
    foo_thread = threading.Thread(target=foo)
    foo_thread.daemon = True
    progressbar.start()
    foo_thread.start()
    root.after(20, check_foo_thread)

def check_foo_thread():
    if foo_thread.is_alive():
        root.after(20, check_foo_thread)
    else:
        progressbar.stop()

root = Tk()
mainframe = ttk.Frame(root, padding="3 3 12 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)
progressbar = ttk.Progressbar(mainframe, mode='indeterminate')
progressbar.grid(column=1, row=100, sticky=W)

ttk.Button(mainframe, text="Check",
           command=lambda:start_foo_thread(None)).grid(column=1, row=200,
                                                       sticky=E)

for child in mainframe.winfo_children():
    child.grid_configure(padx=5, pady=5)
root.bind('<Return>', start_foo_thread)

root.mainloop()
3
votes

Here's another considerably simpler solution that doesn't require mixing Tkinter and multi-threading. To use it requires the ability to call the progressbar widget's update_idletasks() method multiple times during the time-consuming function.

from Tkinter import *
import ttk

import time

def foo(progressbar):
    progressbar.start()
    for _ in range(50):
        time.sleep(.1) # simulate some work
        progressbar.step(10)
        progressbar.update_idletasks()
    progressbar.stop()

root = Tk()

mainframe = ttk.Frame(root, padding="3 3 12 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)
progressbar = ttk.Progressbar(mainframe, mode='indeterminate')
progressbar.grid(column=1, row=100, sticky=W)

ttk.Button(mainframe, text="Check",
           command=lambda:foo(progressbar)).grid(column=1, row=200, sticky=E)

for child in mainframe.winfo_children():
    child.grid_configure(padx=5, pady=5)
root.bind('<Return>', lambda event:foo(progressbar))

root.mainloop()