QWidget.update() or repaint() not refreshing the QWidget

Question

I am trying to create a GUI application in python using PyQt5 and wanted to implement splash screen in it. The problem is that after hiding the splash screen image I add a button to the same QWidget and call update() but it isn't showing.

Code

import sys
from PyQt5.QtWidgets import QApplication, QLabel, QWidget,QPushButton
from PyQt5.QtGui import QCursor,QPixmap
from PyQt5.QtCore import Qt,QTimer

class classer:
   def __init__(self):
      self.w=QWidget()
      self.w.setFixedSize(640,480)
      self.w.setWindowTitle("Classer")

   def splashScreen(self):
      img = QLabel(self.w)
      img.setGeometry(0,0,640,480)
      pixmap = QPixmap('SplashScreen.png')
      img.setPixmap(pixmap.scaled(640,480,Qt.KeepAspectRatio))
      self.w.show()
      QTimer.singleShot(2000, img.hide)

   def mainScreen(self):
      btn=QPushButton(self.w)
      btn.setText('Click')
      btn.move(270,228)
      btn.setCursor(QCursor(Qt.PointingHandCursor))
      self.w.update()
      print("reached here!")

   def run(self):
      self.splashScreen()
      self.mainScreen()
      sys.exit(app.exec_())
    
if __name__ == '__main__':
   app = QApplication([])
   app.setStyleSheet(open('StyleSheet.css').read())
   instance=classer()
   instance.run()

Splash Screen

Current state after hiding image and calling .update()

Desired state after hiding image and calling .update()

Answer 1

The method update will only work on visible widgets (doc), and the QPushButton is not visible since the w.show() method is called before the button creation. So you don't really need update here.

You can achieve this by moving some lines, like below :

   def splashScreen(self):
      img = QLabel(self.w)
      img.setGeometry(0,0,640,480)
      pixmap = QPixmap('background.png')
      img.setPixmap(pixmap.scaled(640,480,Qt.KeepAspectRatio))    
      QTimer.singleShot(2000, img.hide)

   def mainScreen(self):
      btn=QPushButton(self.w)
      btn.setText('Click')
      btn.move(270,228)
      btn.setCursor(QCursor(Qt.PointingHandCursor))

   def run(self):    
      self.mainScreen()   # --> paint the button
      self.splashScreen() # --> paint the img on top layer
      self.w.show()       # --> display the widget

It's better to keep self.w.show() outside splashScreen, the whole widget will not depend on the splash display (in case you want to comment self.splashScreen() to save 2sec each time you run the program, for example).