[PyQt] How to change the value which is shown on GUI

[Johoski, Timothy R]

> From: pyqt-bounces at riverbankcomputing.com [mailto:pyqt-bounces at riverbankcomputing.com] On Behalf Of ??
> Sent: Friday, July 26, 2013 9:45 AM
> To: pyqt at riverbankcomputing.com
> Subject: [PyQt] How to change the value which is shown on GUI
> 
> Hello list, I want to design a battery monitoring system via raspberrypi. The voltage of battery is real changing data, I try to write some code, but the voltage can not change when I change the value of voltage.
>  
> here is part of my code:
>  
> import sys
> from PyQt4 import QtGui,QtCore
> import time
>  
> class Example(QtGui.QWidget):
>      
>         def __init__(self):
>               super(Example,self).__init__()
>  
>               self.initUI()
>  
>          def initUI(self):
>                voltage=12 #e.g. I get the value of voltage is 12v
>                
>                voltageEdit=QtGui.QLabel(str(voltage),self)
>                voltageEdit.resize(voltageEdit.sizeHint())
>                voltageEdit.move(160,100)
>  
>                time.sleep(5) # I want the GUI shows another value of voltage 5 seconds later
>  
>                voltage=22
>                voltageEdit=QtGui.QLabel(str(voltage),self)
>                voltageEdit.resize(voltageEdit.sizeHint())
>                voltageEdit.move(160,100)
>  
>                grid=QtGui.QGridLayout()
>                self.setLayout(grid)
>  
>                self.setGeometry(300,200,600,400)
>                self.setWindowTitle("battery status")
>                self.show()
>  
> def main():
>         
>          app=QtGui.QApplication(sys.argv)
>          ex=Example()
>          sys.exit(app.exec())
>  
> if __name__='__main__':
>          main()
>  
>  
> When I executed this code, GUI shows the voltage is 12, and it will not change, please tell me how to fix it.
>  
> thanks in advance,
>  
> Harry

hi Harry, the following illustrates how to update the label every 5 seconds using a QTimer.  In the original code, time.sleep(5) will actually put the application to sleep and Qt will not process any events (mouse motion, button presses, repaint events, etc).  But in the code below, QTimer.singleShot "schedules" the updateLabel function to be called in 5 seconds.  QTimer.singleShot returns immediately, allowing the next lines of code to run and show the widget on the screen.  5 seconds later, Qt calls updateLabel which changes the voltage text (and then schedules another call to itself 5 more seconds from now).
Hope this helps.
- Tim

import sys
from PyQt4 import QtGui,QtCore
import time
 
class Example(QtGui.QWidget):
     
        def __init__(self):
              super(Example,self).__init__()
 
              self.initUI()
 
        def initUI(self):
              voltage=12 #e.g. I get the value of voltage is 12v
               
              voltageEdit=QtGui.QLabel(str(voltage),self)
              voltageEdit.resize(voltageEdit.sizeHint())
              voltageEdit.move(160,100)
 
              # after 5 seconds (5000 milliseconds), call self.updateLabel
              QtCore.QTimer.singleShot(5000, lambda: self.updateLabel(voltageEdit))
 
              grid=QtGui.QGridLayout()
              self.setLayout(grid)
 
              self.setGeometry(300,200,600,400)
              self.setWindowTitle("battery status")
              self.show()
 
        def updateLabel(self, voltageEdit):
              # change the following line to retrieve the new voltage from the device
              newvoltage=int(voltageEdit.text()) + 1
              voltageEdit.setText(str(newvoltage))
              QtCore.QTimer.singleShot(5000, lambda: self.updateLabel(voltageEdit))
 
def main():
        
         app=QtGui.QApplication(sys.argv)
         ex=Example()
         sys.exit(app.exec_())
 
if __name__=='__main__':
         main()