Can't use X at top, right of app to stop the app have while loop is running

tran con

hello guy! i have this problem:

i use qt designer 5.14.1 to make an app and use pycharm to make python code
if in my code have while loop and i try to stop the program with X at top, right of app it's not working, my app is freeze and error
i can stop while loop with a button use thread and keyboard, but it's not a good program, because nowadays all apps are off by click X at top, right of app
please help me, how can i use X to stop the app have while loop inside

eyllanesc

@tran-con Please provide minimal compilable code because the solution depends on your implementation.

tran con

@eyllanesc here is my code

import sys

from PyQt6.QtWidgets import QApplication, QMainWindow

from gui import Ui_MainWindow
import time

class MainWindow:
def init(self):

    self.main_win = QMainWindow()
    self.uic = Ui_MainWindow()
    self.uic.setupUi(self.main_win)
    self.uic.Button_read_cell.clicked.connect(self.start_while)

def start_while(self):
    print("start run")
    global a
    a = True
    self.while_loop()
def while_loop(self):
    print("ready")
    while a == True:
        time.sleep(0.5)
        print('run')

def show(self):
    
    self.main_win.show()

if name == "main":

app = QApplication(sys.argv)
main_win = MainWindow()
main_win.show()
sys.exit(app.exec())

eyllanesc

@tran-con You say: i can stop while loop with a button use thread and keyboard, could you show that code?

tran con

this code stop while loop by use thread method
sorry about the way it show the code, i don't know why it show all the code like that
hope in future i can stop the app only press X at top, right of the app
if you want the code to stop while loop with the keyboard tell me

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow
from gui import Ui_MainWindow
import time
import threading
class MainWindow:
def init(self):
self.main_win = QMainWindow()
self.uic = Ui_MainWindow()
self.uic.setupUi(self.main_win)
self.uic.Button_read_cell.clicked.connect(self.start_while)
self.uic.Button_add_row.clicked.connect(self.stop_while)
def stop_while(self):
print("stop")
global a
a = False
def start_while(self):
print("start run")
global a
a = True
self.while_loop()
def while_loop(self):
print("ready")
def run():
while a == True:
time.sleep(0.5)
print('run')
if a == False:
break
t1 = threading.Thread(target=run)
t1.start()

def show(self):
    self.main_win.show()

if name == "main":
app = QApplication(sys.argv)
main_win = MainWindow()
main_win.show()
sys.exit(app.exec())

eyllanesc

@tran-con I think that is the correct way since you should not execute a while loop in the main thread and less use time.sleep. The only bad thing is that you use global variables.

tran con

@eyllanesc please give me an example the code to stop the while loop with "X close" button

SimonSchroeder

The basic idea is quite simple: A single thread can only do one thing at a time. If you let it handle your while loop it cannot respond to user interactions at the same time. The main thread (which will start running when you start your application) has an event loop running which will react to mouse and keyboard input (besides other things). Whenever you block the main thread (in your case by running you own loop) it cannot handle any input. Even the sleep will put the main thread to sleep and not allow the event loop to run instead. You should return to the main thread as soon as possible (in Qt, but also in any GUI application) for your app to stay reactive. Putting your workload into a separate thread is one common solution.

I am not sure about your real application of a while loop. However, if you do sleeps in between you might want to try a timer instead. For each timeout there will be an event in the event loop. But, this event is interleaved with other events. This would avoid blocking any input from happening.

Another trick is to call QCoreApplication.processEvents every now and then in your own loop. This will also process the event which are stuck in the event loop you are blocking. From my own experience this approach can slow your actual work down by a lot if you have a really heavy workload. Using a separate thread is preferred then.