How to control QProgressBar with Signal

Question

Pushing the button starts 100 rounds cycle. With QLabel.setText() we update self.label from inside of scope of clicked() function.

Answer 1

The code declares a local progressbar object connected to a custom 'customSignal` using:

QtCore.QObject.connect(self, QtCore.SIGNAL("customSignal(int)"), progressbar, QtCore.SLOT("setValue(int)"))

with four arguments passed to QtCore.QObject.connect().

The first argument self is the object that will be emitting the signal. Since the function that will do the "sleep-every-second-processing" is declared under the main Dialog instance we pass self here.

The second argument is the name of the signal itself: 'customSignal'.

The progressbar object is used as third and its method setValue as fourth last argument.

class ProgressBar(QtGui.QProgressBar):
    def __init__(self, parent=None):
        super(ProgressBar, self).__init__(parent=parent)

class Dialog(QtGui.QDialog):
    def __init__(self):
        super(QtGui.QDialog,self).__init__()
        layout = QtGui.QVBoxLayout()
        self.setLayout(layout)
        self.label = QtGui.QLabel('idle...')
        layout.addWidget(self.label)

        progressbar = ProgressBar(self)
        QtCore.QObject.connect(self, QtCore.SIGNAL("customSignal(int)"), progressbar, QtCore.SLOT("setValue(int)"))

        layout.addWidget(progressbar) 

        button = QtGui.QPushButton('Process')
        button.clicked.connect(self.clicked)
        layout.addWidget(button) 

    def clicked(self):
        for value in range(101):
            message = '...processing %s of 100'%value
            self.label.setText(message)
            self.emit(QtCore.SIGNAL("customSignal(int)"), value)
            QtGui.qApp.processEvents()
            time.sleep(1)


if __name__ == '__main__':
    app = QtGui.QApplication([])
    dialog = Dialog()
    dialog.resize(300, 100)
    dialog.show()
    app.exec_()

--------------------

Here is variation of the same solution except linking to the progressbar method. import time

class ProgressBar(QtGui.QProgressBar):
    def __init__(self, parent=None):
        super(ProgressBar, self).__init__(parent=parent)

    def set_to_value(self, value):
        self.setValue(value)
        QtGui.qApp.processEvents()
        return True

    def closeEvent(self, event):
        self._active=False

class Dialog(QtGui.QDialog):
    def __init__(self):
        QtGui.QDialog.__init__(self, parent=None)
        layout = QtGui.QVBoxLayout()
        self.setLayout(layout)
        self.label = QtGui.QLabel('idle...')
        layout.addWidget(self.label)

        progressbar = ProgressBar(self)
        QtCore.QObject.connect(self, QtCore.SIGNAL("customSignal(int)"), progressbar.set_to_value )
        layout.addWidget(progressbar) 

        button = QtGui.QPushButton('Process')
        button.clicked.connect(self.clicked)
        layout.addWidget(button) 

    def clicked(self):
        for value in range(101):
            message = '...processing %s of 100'%value
            self.label.setText(message)
            self.emit(QtCore.SIGNAL("customSignal(int)"), value)
            QtGui.qApp.processEvents()
            time.sleep(1)

if __name__ == '__main__':
    app = QtGui.QApplication([])
    dialog = Dialog()
    dialog.resize(300, 100)
    dialog.show()
    app.exec_()

======================

This code now links a custom signal to a function referred as Slot in Qt.

from PySide import QtCore, QtGui
import time

class ProgressBar(QtGui.QProgressBar):
    def __init__(self, parent=None):
        super(ProgressBar, self).__init__(parent=parent)

    @QtCore.Slot(int)
    def set_to_value(self, value):
        self.setValue(value)
        QtGui.qApp.processEvents()
        return True

    def closeEvent(self, event):
        self._active=False

class Dialog(QtGui.QDialog):
    def __init__(self):
        QtGui.QDialog.__init__(self, parent=None)
        layout = QtGui.QVBoxLayout()
        self.setLayout(layout)
        self.label = QtGui.QLabel('idle...')
        layout.addWidget(self.label)

        progressbar = ProgressBar(self)
        # QtCore.QObject.connect(self, QtCore.SIGNAL("customSignal(int)"), progressbar.set_to_value )
        QtCore.QObject.connect(self, QtCore.SIGNAL("customSignal(int)"), progressbar, QtCore.SLOT("set_to_value(int)"))

        layout.addWidget(progressbar) 

        button = QtGui.QPushButton('Process')
        button.clicked.connect(self.clicked)
        layout.addWidget(button) 

    def clicked(self):
        for value in range(101):
            message = '...processing %s of 100'%value
            self.label.setText(message)
            self.emit(QtCore.SIGNAL("customSignal(int)"), value)
            QtGui.qApp.processEvents()
            time.sleep(1)

if __name__ == '__main__':
    dialog = Dialog()
    dialog.resize(300, 100)
    dialog.show()