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Tkinter: How to use threads to preventing main event loop from "freezing"
(5 answers)
Closed 4 years ago.
I wanted to create a non-blocking message window with Tkinter. This in order to display a wait message, when another function is waiting for a reply. Once the reply is received the window can be closed automatically. I managed to find some info on the web and I made the following:
import tkinter as tk
import threading
import time
class Show_Azure_Message(threading.Thread):
def __init__(self, message):
self.thread = threading.Thread.__init__(self)
self.message = message
self.start()
#staticmethod
def callback():
return
def destroy(self):
self.root.quit()
#run will be called from self.start()
def run(self):
self.root = tk.Tk()
self.root.protocol("WM_DELETE_WINDOW", self.callback)
self.t2 = tk.Text(self.root, height=10, borderwidth=0, wrap=tk.WORD)
self.t2.insert(1.0, self.message)
self.t2.grid(padx=5,row=2)
self.t2.config(state=tk.DISABLED)
self.root.mainloop()
App = Show_Azure_Message('Hello')
for i in range(0,2):
print(i)
time.sleep(1)
App.destroy()
This runs fine when I execute this as main script, but when I want to run another gui application with Tkinter right after i get the following error
RuntimeError: main thread is not in main loop
Also when I run another piece of code after the App.destroy(). Then the App window doesn't close end the application keeps running.
root = tk.Tk()
label = tk.Label(root, text='Hello2')
label.pack()
root.mainloop()
So probably I am doing something wrong but I cannot find out what the problem is. Next to that I don't have much experience with Python Threads hence maybe I am missing something trivial over here.
regards,
Geert
I think, if you really want to do it that way (look in the comment section of your post) you should use a Toplevel window instead since they don't need a mainloop which is making things way more easy in my eyes.
That's some kind of how I would do it if I would have to:
from tkinter import *
import threading
import time
class Show_Azure_Message(Toplevel):
def __init__(self,master,message):
Toplevel.__init__(self,master) #master have to be Toplevel, Tk or subclass of Tk/Toplevel
self.title('')
self.attributes('WM_DELETE_WINDOW',self.callback)
self.resizable(False,False)
Label(self,text=message,font='-size 25').pack(fill=BOTH,expand=True)
self.geometry('250x50+%i+%i'%((self.winfo_screenwidth()-250)//2,(self.winfo_screenheight()-50)//2))
def callback(self): pass
BasicApp=Tk()
App = Show_Azure_Message(BasicApp,'Hello')
for i in range(0,2):
print(i)
time.sleep(1)
App.destroy()
Related
I have the following problem: I would like to create a GUI with tkinter, that reacts to signals, sent from a socket. For example, I would like to be able to terminate the application, when an end signal is received.
For that purpose I have a function, running in a separate thread, that listens for signals and acts accordingly. However, when I try to destroy the tkinter-GUI, the programm stops, and gives this error message:
Fatal Python error: PyEval_RestoreThread: the function must be called with the GIL held, but the GIL is released (the current Python thread state is NULL)
Python runtime state: initialized
I have recreated this minimum working example giving the same behavior:
import tkinter as tk
import time
import threading
class Gui(tk.Frame):
"""Minimal GUI with only a button"""
def __init__(self, master: tk.Tk):
tk.Frame.__init__(self, master)
self.pack()
tk.Button(self, text='Spam').pack()
class Client:
"""Client for handling signals"""
def __init__(self, master: tk.Tk):
self.master = master
self.gui = Gui(self.master)
self.signal = None # Initialize signal
self.thread = threading.Thread(target=self.listen_thread)
self.running = True
self.thread.start()
def listen_thread(self):
"""Listen for signals and handle actions"""
while self.running:
signal = self.signal # Dummy signal, set by external method, instead of received message from socket
if signal == 'end': # End signal received
self.master.destroy() # Destroy tkinter GUI, error occurs here
self.running = False # Terminate while loop
else:
time.sleep(0.2)
def send_signal_after(receiver: Client, delay: float = 2.0):
"""Send a signal to the client after short delay"""
time.sleep(delay)
receiver.signal = 'end'
if __name__ == '__main__':
root = tk.Tk()
client = Client(root)
threading.Thread(target=send_signal_after, args=(client,)).start()
root.mainloop()
if client.thread: # Check if thread is still running, if so, wait for termination
client.thread.join()
I am running this on MacOS 12.1, Python 3.10.
Is there any other way to terminate the application? I know, I could probably use sys.exit(), but I would like to do this in a cleaner way.
Thank you!
So, to understand how to do it, I made an example:
This is the first file (the main one) :
import tkinter as tk
from tkinter import *
import threading
import file2 as file2
def func(gui):
# just some code around here
# start up the program
root = Tk()
# pass the root in the __init__ function from file2
mainGui = file2.file2Class(root)
# Start the new thread
theThread = threading.Thread(target=func, args=([mainGui]))
theThread.daemon = True
theThread.start()
# loop command
tk.mainloop()
And this is file2 :
import tkinter as tk
from tkinter import *
class file2Class:
root = None
def __init__(self, initialRoot):
self.root = initialRoot
self.createUI();
def createUI(self):
# This is an exit button
tk.Button(
self.root,
text="Exit",
font = "Verdana 10 bold",
fg="red",
command=self.root.destroy, # <- this is the exit command
width=25,
height=2).grid(row=0,column=0)
So, the most important thing is to make sure that you pass root in the args of the thread.
I hope I helped you!
I have created a tkinter GUI in the following structure:
import tkinter as tk
import threading
class App:
def __init__(self, master):
self.display_button_entry(master)
def setup_window(self, master):
self.f = tk.Frame(master, height=480, width=640, padx=10, pady=12)
self.f.pack_propagate(0)
def display_button_entry(self, master):
self.setup_window(master)
v = tk.StringVar()
self.e = tk.Entry(self.f, textvariable=v)
buttonA = tk.Button(self.f, text="Cancel", command=self.cancelbutton)
buttonB = tk.Button(self.f, text="OK", command=threading.Thread(target=self.okbutton).start)
self.e.pack()
buttonA.pack()
buttonB.pack()
self.f.pack()
def cancelbutton(self):
print(self.e.get())
self.f.destroy()
def okbutton(self):
print(self.e.get())
def main():
root = tk.Tk()
root.title('ButtonEntryCombo')
root.resizable(width=tk.NO, height=tk.NO)
app = App(root)
root.mainloop()
main()
I want to prevent the GUI from freezing when running a function (in the example code it's the function of the ok-button). For that I found the solution of using the thread-module as best practice. But the problem is that when I want to run the code once again, python returns this traceback:
RuntimeError: threads can only be started once
I'm totally aware of the problem that threads can be only starten once as stated in the error message. My question is: How can I stop a thread to start it a second time or does anybody has a better workaround for preventing the GUI from freezing and pressing a button/running a function multiple times?
BR and thank you
Lorenz
Your code will only create one thread and assign its start function reference to command option. Therefore same start() function will be called whenever the button is clicked.
You can use lambda instead:
command=lambda: threading.Thread(target=self.okbutton).start()
Then whenever the button is clicked, a new thread will be created and started.
I have a main tkinter window that can take up to a few seconds to load properly. Because of this, I wish to have a splash screen that shows until the init method of the main class has finished, and the main tkinter application can be shown. How can this be achieved?
Splash screen code:
from Tkinter import *
from PIL import Image, ImageTk
import ttk
class DemoSplashScreen:
def __init__(self, parent):
self.parent = parent
self.aturSplash()
self.aturWindow()
def aturSplash(self):
self.gambar = Image.open('../output5.png')
self.imgSplash = ImageTk.PhotoImage(self.gambar)
def aturWindow(self):
lebar, tinggi = self.gambar.size
setengahLebar = (self.parent.winfo_screenwidth()-lebar)//2
setengahTinggi = (self.parent.winfo_screenheight()-tinggi)//2
self.parent.geometry("%ix%i+%i+%i" %(lebar, tinggi, setengahLebar,setengahTinggi))
Label(self.parent, image=self.imgSplash).pack()
if __name__ == '__main__':
root = Tk()
root.overrideredirect(True)
progressbar = ttk.Progressbar(orient=HORIZONTAL, length=10000, mode='determinate')
progressbar.pack(side="bottom")
app = DemoSplashScreen(root)
progressbar.start()
root.after(6010, root.destroy)
root.mainloop()
Main tkinter window minimum working example:
import tkinter as tk
root = tk.Tk()
class Controller(tk.Frame):
def __init__(self, parent):
'''Initialises basic variables and GUI elements.'''
frame = tk.Frame.__init__(self, parent,relief=tk.GROOVE,width=100,height=100,bd=1)
control = Controller(root)
control.pack()
root.mainloop()
EDIT: I can use the main window until it has finished loading using the .withdraw() and .deiconify() methods. However my problem is that I cannot find a way to have the splash screen running in the period between these two method calls.
a simple example for python3:
#!python3
import tkinter as tk
import time
class Splash(tk.Toplevel):
def __init__(self, parent):
tk.Toplevel.__init__(self, parent)
self.title("Splash")
## required to make window show before the program gets to the mainloop
self.update()
class App(tk.Tk):
def __init__(self):
tk.Tk.__init__(self)
self.withdraw()
splash = Splash(self)
## setup stuff goes here
self.title("Main Window")
## simulate a delay while loading
time.sleep(6)
## finished loading so destroy splash
splash.destroy()
## show window again
self.deiconify()
if __name__ == "__main__":
app = App()
app.mainloop()
one of the reasons things like this are difficult in tkinter is that windows are only updated when the program isn't running particular functions and so reaches the mainloop. for simple things like this you can use the update or update_idletasks commands to make it show/update, however if the delay is too long then on windows the window can become "unresponsive"
one way around this is to put multiple update or update_idletasks command throughout your loading routine, or alternatively use threading.
however if you use threading i would suggest that instead of putting the splash into its own thread (probably easier to implement) you would be better served putting the loading tasks into its own thread, keeping worker threads and GUI threads separate, as this tends to give a smoother user experience.
I want to create a GUI in tkinter that not only executes commands when a button is pressed, but responds to the state of a larger script running in a separate thread.
I have really dug around and tried to find some information on message passing, and I have found some great info on the pickle module, using multiprocessing and its built in tools and also threading, and queuing. I have even dug into David Beazley's lesson on concurrency located here. I just can't get the syntax right on any of those methods.
I have broken down my code into a small functional unit that should launch a little tkinter window like this:
tkinter window
The code below has a "launchGUI" function that launches my tkinter GUI, a "myLoop" function that starts the threads and will also loop to drive my larger program later, right now it just rotates the blink variable. I also have a blinkCheck method in my class that checks the status of the blink variable in the class.
I don't know if I am even putting my message receiver in the right place. In the following example code I am just trying to pass a global variable into the class. I know it is getting into the class, because the blinkCheck() method works even though uncommenting that method crashes the window. However, with the method turned off the label in the GUI never changes. I think the window crashing is the least of my worries, it must be because i have another while loop running.
What is the correct way to get that number in Label to change?
Here is my example code:
import tkinter as tk
from tkinter import Frame, Label
import time
import threading
blink = 0
class MyClass(tk.Frame):
def __init__(self, master):
self.master = master
super().__init__(self.master)
global blink
self.label = Label(master, text=blink)
self.label.pack()
#self.blinkCheck()
def blinkCheck(self):
global blink
while True:
print("blink in blinkCheck method is = {}".format(blink))
time.sleep(2.5)
def launchGUI():
root = tk.Tk()
root.title("My Blinker")
app1 = MyClass(root)
app1.mainloop()
def myLoop():
global blink
t1=threading.Thread(target=launchGUI)
t1.daemon = True
t1.start()
print("blink in blinker function is {}".format(blink))
while True:
if blink == 0:
blink = 1
else:
if blink == 1:
blink = 0
time.sleep(2.5)
if __name__=="__main__":
myLoop()
In your description you have mentioned something about involving buttons. I do not see that in your provided snippet. But with buttons it is possible to configure the label, i.e:
from tkinter import Label, Button
blink = 0
class MyClass(tk.Frame):
def __init__(self, master):
self.master = master
super().__init__(self.master)
global blink
self.label = Label(master, text=blink)
self.button = Button(master, text="Button", command=lambda: foo(self.label))
self.label.pack()
self.button.pack()
#self.blinkCheck()
def blinkCheck(self):
global blink
while True:
print("blink in blinkCheck method is = {}".format(blink))
time.sleep(2.5)
def foo(self, label):
label.config(text=blink)
Conventionally, this would be the most simple way to configure a label within an active thread.
If anyone feels like this answer may not be fully correct, please do edit it because I am new to Stack Overflow!
First, the GUI must run in main thread, and must not blocked by a infinite loop. Use after instead. To communicate, use some appropriate object from threading, e.g. Event:
import tkinter as tk
import time
import threading
class MyClass(tk.Frame):
def __init__(self, master, event):
super().__init__(master)
self.master = master
self.event = event
self.label = tk.Label(master, text='')
self.label.pack()
self.after(100, self.blink_check)
def blink_check(self):
self.label['text'] = self.event.is_set()
self.after(100, self.blink_check)
def blink(event):
while True:
event.set()
time.sleep(2.5)
event.clear()
time.sleep(2.5)
def main():
root = tk.Tk()
root.title("My Blinker")
event = threading.Event()
t = threading.Thread(target=blink, args=(event,))
t.daemon = True
t.start()
frame = MyClass(root, event)
root.mainloop()
if __name__=="__main__":
main()
I'm trying to create a simple Python GUI (with Tkinter) with start button, running a while loop in a thread, and a stop button to stop the while loop.
I'm having issue with the stop button, which doesn't stop anything and frozen GUI once the start button is clicked.
See code below:
import threading
import Tkinter
class MyJob(threading.Thread):
def __init__(self):
super(MyJob, self).__init__()
self._stop = threading.Event()
def stop(self):
self._stop.set()
def run(self):
while not self._stop.isSet():
print "-"
if __name__ == "__main__":
top = Tkinter.Tk()
myJob = MyJob()
def startCallBack():
myJob.run()
start_button = Tkinter.Button(top,text="start", command=startCallBack)
start_button.pack()
def stopCallBack():
myJob.stop()
stop_button = Tkinter.Button(top,text="stop", command=stopCallBack)
stop_button.pack()
top.mainloop()
Any idea how to solve this? I'm sure this is trivial and must have be done thousands of times but I cannot find a solution myself.
Thanks
David
The code is calling run method directly. It will call the method in the main thread. To run it in a separated thread you should use threading.Thread.start method.
def startCallBack():
myJob.start()