Calling a function in the main window from a widget (PySide)

Question

Basicly what I want is:

1. Show a widget in the main window containing a button that opens a QFileDialog
2. When a file is selected the widget containing the button should be switched to a new widget that shows some visualizations which are based on the file content.

In the code example below, this means invoking the open_file() method from the showFileSelectionDialog() method.

The problem is how to do this? I tried taking the parent as argument when initializing the widget and then connecting the button to self.parent.open_file. But this gets complicated and I do not like that the widget is hardcoded to be a child of the main window.

As fair as I can understand, a better approach would be to use Communicate() to emit an event. But then I do not know how to get the file name information to the open_file() method.

#Code greatly inspired by the ZetCode PySide tutorial (http://zetcode.com/gui/pysidetutorial/)

import sys
from PySide import QtGui

class MainApplicationWindow(QtGui.QMainWindow):

    def __init__(self):
        super(MainApplicationWindow, self).__init__()

        self.initUI()

    def initUI(self):

        self.setWindowTitle('<Application title>')
        self.setCentralWidget(FileSelectWidget())
        self.statusBar()

        self.resize(250, 200)
        self.center()
        self.show()

    def center(self):
        qr = self.frameGeometry()
        cp = QtGui.QDesktopWidget().availableGeometry().center()
        qr.moveCenter(cp)
        self.move(qr.topLeft())

    def open_file(self, file_name):
        f = open(file_name, 'r')
        with f:
            data = f.read()
            #TODO: Do something with the data and visualize it!
            print data

class FileSelectWidget(QtGui.QWidget):

    def __init__(self):
        super(FileSelectWidget, self).__init__()

        self.initUI()

    def initUI(self):

        selectLogFilesButton = QtGui.QPushButton('Select log files', self)
        selectLogFilesButton.clicked.connect(self.showFileSelectionDialog)

        hbox = QtGui.QHBoxLayout()
        hbox.addStretch()
        hbox.addWidget(selectLogFilesButton)
        hbox.addStretch()

        vbox = QtGui.QVBoxLayout()
        vbox.addStretch()
        vbox.addLayout(hbox)
        vbox.addStretch()

        self.setLayout(vbox)

    def showFileSelectionDialog(self):

        file_name, _ = QtGui.QFileDialog.getOpenFileName(self, 'Open file', '/home')


def main():

    app = QtGui.QApplication(sys.argv)
    window = MainApplicationWindow()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

Answer 1

The FileSelectWidget class should define a custom signal that can be connected to the open_file slot.

In order to do that, make sure the QtCore module is imported, and then define the custom signal like this:

class FileSelectWidget(QtGui.QWidget):
    fileSelected = QtCore.Signal(object)

Then emit the signal whenever a file is selected:

    def showFileSelectionDialog(self):
        file_name, _ = QtGui.QFileDialog.getOpenFileName(
                           self, 'Open file', '/home')
        if file_name:
            self.fileSelected.emit(file_name)

And finally, connect the signal to the slot:

    widget = FileSelectWidget()
    widget.fileSelected.connect(self.open_file)
    self.setCentralWidget(widget)