Show a Loading Home Dialog before starting MainWindow

[hachbani]

Sorry again, I acknowledge that I've been wasting your time for a stupid mistake I've made pasting the code due to a lack of attention.

[JonB]

@hachbani
That's OK. At least you were polite enough to apologize, which is more than some :)

You may know PyQt5 more than me. But two things come to mind about your signal declaration

self.change_val = QtCore.Signal(int)

• PyQt5 signals should be class members, not instance members?
• You should be using pyqtSignal(int), not QtCore.Signal(int)?
• Similarly, @pyqtSlot decorator instead of @QtCore.Slot(int)? Don't know if that matters.

class MainWindow(QtWidgets.QMainWindow,  Ui_MainWindow):
    change_val = pyqtSignal(int)

Do either of those improve? Reference https://doc.bccnsoft.com/docs/PyQt5/signals_slots.html

[hachbani]

@hachbani said in Show a Loading Home Dialog before starting MainWindow:

I'm using Pyside2, pyothn 3.8

I'm using Pyside2, I'll think more about your first point
PyQt5 signals should be class members, not instance members?

[JonB]

@hachbani said in Show a Loading Home Dialog before starting MainWindow:

I'm using Pyside2,

Damn, so you are, that changes everything! I got distracted because someone called, damn....

PyQt5 signals should be class members, not instance members?

Yes, and I think this applies to PySide2 too, and is the cause of your error message. See 'PySide.QtCore.Signal' object has no attribute 'connect'?

And/or further, does your MainWindow.__init__() call super().__init__()? Omitting that can apparently lead to that error message too.

Finally, since your own signal does not seem to have multiple overloads, you could try plain

change_val.connect(self.set_progress_val)

without that [int].

See also https://wiki.qt.io/Qt_for_Python_Signals_and_Slots

[hachbani]

I've declared change_val as a class member, I get an error name 'change_val' is not defined

I've updated the code in my last comment. I do indeed call super in MainWindow init()

[JonB]

@hachbani said in Show a Loading Home Dialog before starting MainWindow:

've declared change_val as a class member, I get an error name 'change_val' is not defined

Refer the https://wiki.qt.io/Qt_for_Python_Signals_and_Slots I quoted earlier for examples. It may be that to reference the class variable you have to go self.change_val or MainWindow.change_val?

[hachbani]

Thanjs @JonB for you help ! Indeed the self.change_val worked. I get my ProgressDialog, I added some prints in set_progress_val to debug if it's been called correctly, and it is. The problem is the progressDialog freezes, no progress is shown.

Here's the actual code:

class MainWindow(QtWidgets.QMainWindow,  Ui_MainWindow):
    change_val = QtCore.Signal(int)

    def __init__(self, file_name,parent=None):
        """
        super(MainWindow, self).__init__(parent)
        ..
        __init__ code lines
        """

        self.change_val[int].connect(self.set_progress_val)
        self.progress = QtWidgets.QProgressDialog('loading...', 'cancel', 0, 100, self)
        self.progress.setValue(0)
        self.progress.show()
        self.LoadData(d.path)
    
    @QtCore.Slot(int)
    def set_progress_val(self, val):
        print('progress setVal called, new val: ', self.progress.value())
        self.progress.setValue(val)

    def LoadData(self, file_path):
        
        """
        Parsing lines of code
        ..
        self.change_val.emit(30)
        ..
        ..
        self.change_val.emit(60)
        ..
        ..
        """
        self.change_val.emit(100)
        #Parsing finished -> show the mainWindow
        self.show()

class HomeDialog(QtWidgets.QDialog, home_dialog.Ui_Dialog):
    def __init__(self, parent=None):
        super(HomeDialog, self).__init__(parent)
        self.setupUi(self)
        self.openB6.clicked.connect(self.get_file_name)

    def get_file_name(self):
        file_name = QtWidgets.QFileDialog.getOpenFileName(self, 'Open config file',
                                                            dir=path.join("/"),
                                                            filter="B6 (*.b6)")
        if not file_name[0]:
            return None
        else:
            self.path = file_name
            self.accept()

if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    app.setStyle(ProxyStyle())
    d = HomeDialog()
    if d.exec_():
        mainWin = MainWindow(file_name=d.path)
        mainWin.show()
        sys.exit(app.exec_())

Here's a screenshot of the displayed window when progressDialog is displayed:

[JonB]

@hachbani
Because LoadData() is in your GUI thread, Qt does not get to redraw/refresh the UI while it is running. I assume your bar shows once as "full" right at the end? I haven't used QProgressBar, but I imagine you should play with one of the following:

• Move LoadFile() to its own thread. That's the nicest, but can be the most code.

• Try self.progress.repaint() in your slot.

• Try QCoreApplication.processEvents() in your slot.

Is set_progress_val() called against each emit()? I think it is, because you are using DirectConnection; if not you can always call set_progress_val() directly instead of going via a signal.

[hachbani]

Hey, thanks so much man !!! I added QtCore.QCoreApplication.processEvents() to my slot, and it works !!

Maybe I'm going to take a look really later on the first point, about moving LoadData() to another thread, it seems interesting (I just never worked with QThread)

going to update the post with the full solution later, in case It'd save someone's day.

Have a nice week

[JonB]

@hachbani
Threads are tempting, especially for beginners, but nasty to get right, and I think more of an issue in Python than C++.

processEvents() is a bit "naughty", but awfully simple if it works. You probably have more important things to move onto than spending ages on a loading progress screen :)

The only thing is: if your LoadData() takes a bit of time, try clicking on something on the main window which has a slot action while it is still loading the data. The problem is that slot will execute, and if it expects your data load to be complete it won't be.

Have a look at the example at https://doc.qt.io/qt-5/qprogressdialog.html#details where

Compared to a modeless QProgressDialog, a modal QProgressDialog is simpler to use for the programmer. Do the operation in a loop, call setValue() at intervals

Is that code implying you can call QProgressDialog.setValue() as you go along without you having to worry about the event loop for updates? If that pattern works for you I'd be tempted to adopt it?