How to quit the program in while loop using push-button in PyQt

Question

I have the following code which will start after clicking the 'Start' button in PyQt:

def Start(self):
  import time
  import os
  import RPi.GPIO as GPIO
  import datetime

  GPIO.setmode(GPIO.BCM)
  DEBUG = 1

  os.system('clear')

  # SPI port on GPIO
  SPICLK = 18
  SPIMISO = 23
  SPICS = 25

  # set up the SPI interface pins
  GPIO.setup(SPIMISO, GPIO.IN)
  GPIO.setup(SPICLK, GPIO.OUT)
  GPIO.setup(SPICS, GPIO.OUT)

  GPIO.output(SPICS, True)
  GPIO.output(SPICS, False) # bring CS low
  while True:
        adcout = 0             
        read_adc = 0
        #s=time.clock()
        for i in range(25):
            GPIO.output(SPICLK, True)
            GPIO.output(SPICLK, False)
            adcout <<= 1
            if (GPIO.input(SPIMISO)==1):
                adcout |= 0x1
        time.sleep(0.085)   
        if (GPIO.input(SPIMISO)==0):
            read_adc = adcout
            millivolts = read_adc * ( 2500.0 /(pow(2,22)))
            read_adc = "%d" % read_adc
            millivolts = "%d" % millivolts

        if DEBUG:
            print millivolts, "mV (ADC)"

The above program is for ADC reading and it will start after clicking the pushbutton called 'Start' as : self.pushButton.clicked.connect( self.Start)

And I have another pushButton_2 called 'Stop' and by clicking this the above process should stop.Please suggest, so I can able to do that.

Answer 1

There is no need to do anything other than what I suggested in your other question on this topic: just use processEvents . As long as you can call it frequently enough (but not too frequently), it should do exactly what you want. Using your second example, the following works fine for me:

  def Start(self):
    if not self.started:
        self.started = True
        self.StartLoop()

  def Stop(self):
    if self.started:
        self.started = False

  def StartLoop(self):
    DEBUG = 1
    while self.started:
        print "LED on "
        time.sleep(0.05)
        print "LED off "
        time.sleep(0.085)
        QtGui.qApp.processEvents()

Answer 2

1. This question is useful: tkinter loop and serial write It could be copied over with two changes: master.update becomes QtGui.qApp.processEvents and master.after becomes QTimer.singleShot .

2. Here is a sketch of how to do what you ask for with guiLoop :

    from guiLoop import guiLoop, stopLoop # ... means fill in your code class ...: started = False def Start(self): if not self.started: # you can also use threads here, see the first link self.started = self.StartLoop() def Stop(self): if self.started: stopLoop(self.started) self.started = False @guiLoop def StartLoop(self): # This is your Start function # ... while True: # ... yield 0.085 # time.sleep(0.085) equivalent # ... 

   Since I do not know what your code look like, here is a working example using PyQT4 and guiLoop :

    from PyQt4 import QtGui import sys from guiLoop import guiLoop # https://gist.github.com/niccokunzmann/8673951 @guiLoop def led_blink(argument): while 1: print("LED on " + argument) yield 0.5 # time to wait print("LED off " + argument) yield 0.5 app = QtGui.QApplication(sys.argv) w = QtGui.QWidget() w.resize(250, 150) w.move(300, 300) w.setWindowTitle('Simple') w.show() led_blink(w, 'shiny!') sys.exit(app.exec_()) 

   guiLoop uses QTimer.singleShot(time, function) to make the loop continue.

   You can also stop the loop with stopLoop() of guiLoop.