PyQt progress bar not updating or appearing until 100%

Question

EDIT: There are a number of similar posts on PyQt4 progress bars not updating. They all focus on the issue of threads & where the program actually updates the window. Although helpful, my code was so structured that the replies were not practical. The accepted answer given here is simple, to the point & works.

I am using Python 2.7 and PyQT 4 on a Win 7 x64 machine.

I am trying to clear my window of one widget, an 'Accept' button, see code, and replace it with a progress bar.

Even though I close the 'Accept' button & add the progress bar before the processing loop is entered into. The window is only updated after the loop has finished & the progress bar jumps straight to 100%.

My code,

from PyQt4 import QtCore, QtGui
import sys
import time

class CentralWidget(QtGui.QWidget):

    def __init__(self, parent=None):
        super(CentralWidget, self).__init__(parent)

        # set layouts
        self.layout = QtGui.QVBoxLayout(self)

        # Poly names
        self.pNames = QtGui.QLabel("Import file name", self)  
        self.polyNameInput = QtGui.QLineEdit(self) 

        # Polytype selection
        self.polyTypeName = QtGui.QLabel("Particle type", self)
        polyType = QtGui.QComboBox(self)
        polyType.addItem("")
        polyType.addItem("Random polyhedra")
        polyType.addItem("Spheres")
        polyType.addItem("Waterman polyhedra")
        polyType.activated[str].connect(self.onActivated)

        # Place widgets in layout        
        self.layout.addWidget(self.pNames)
        self.layout.addWidget(self.polyNameInput)
        self.layout.addWidget(self.polyTypeName)
        self.layout.addWidget(polyType)
        self.layout.addStretch()

    # Combobox choice
    def onActivated(self, text):

        if text=="Random polyhedra":
            self.randomPolyhedra(text)     
        if text=="Spheres":         # not implementaed yet
            self.polyTypeName.setText("Not implemented yet.")
            self.polyTypeName.adjustSize()      
        if text=="Waterman polyhedra": # not implementaed yet
            self.polyTypeName.setText("Not implemented yet.")
            self.polyTypeName.adjustSize()   

    # New options for random polyhedra choice    
    def randomPolyhedra(self, text):    

        self.polyNumberLbl = QtGui.QLabel("How many: ", self)            
        self.polyNumber = QtGui.QLineEdit(self) 
        self.acceptSeed = QtGui.QPushButton('Accept') # Accept button created
        self.acceptSeed.clicked.connect(lambda: self.ranPolyGen())
        self.layout.addWidget(self.polyNumberLbl)
        self.layout.addWidget(self.polyNumber)
        self.layout.addWidget(self.acceptSeed)      # Accept button in layout
        self.randFlag = True
        self.polyTypeName.setText(text)
        self.polyTypeName.adjustSize()

    # Act on option choices for random polyhedra 
    def ranPolyGen(self):

        polyCount = int(self.polyNumber.text())
        self.progressBar = QtGui.QProgressBar() # Progress bar created
        self.progressBar.setMinimum(1)
        self.progressBar.setMaximum(polyCount)
        self.acceptSeed.close()                 # Accept button closed
        self.layout.addWidget(self.progressBar) # Add progressbar to layout
        for poly in range(1, polyCount+1):
            time.sleep(1) # Calls to main polyhedral generating code go here
            print poly
            self.progressBar.setValue(poly)
        self.doneLbl = QtGui.QLabel("Done", self)
        self.layout.addWidget(self.doneLbl)

# Creates GUI
class Polyhedra(QtGui.QMainWindow):

    def __init__(self):

        super(Polyhedra, self).__init__()

        # Place central widget in layout
        self.central_widget = CentralWidget(self)
        self.setCentralWidget(self.central_widget)

        # Set up window        
        self.setGeometry(500, 500, 300, 300)
        self.setWindowTitle('Pyticle')
        self.show()

    # Combo box
    def onActivated(self, text):

        self.central_widget.onActivated(text)


def main():

    app = QtGui.QApplication(sys.argv)
    poly = Polyhedra()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

Below is a picture of during loop execution & after completion.

I dont think I have got my head around the addWidget() method. I was under the impression that this would add another widget to the present layout (a vbox layout here) & that the .close() method removed a widget when directed to do so.

What am I missing?

Answer 1

You can add:

from PyQt4.QtGui import QApplication

Then in your for loop:

QApplication.processEvents() 

Your app is actually becoming unresponsive, you need to call processEvents() to process the events and redraw the gui. I am not overly familiar with pyqt but I imagine another alternative is using a thread.