I Need Help with PyQt5 - Problem with QPushButton Signal and Slot

q&a
1

Hello everyone, :smiling_face_with_three_hearts:

I just starting out with PyQt5, and I am stuck trying to get a button to call a function. I have been learning Python for a couple months and wanted to build a basic GUI app. I followed some tutorials online, but for some reason, clicking the button doesn’t seem to run the function I made.

Here is a stripped-down version of my code, in case it helps:

lass Controller:
def __init__(self, view):
    self._view = view
    self._connectSignals()


def _connectSignals(self):
    self._view.button.clicked.connect(self._calculate)


def _calculate(self):
    print('trying to calculate')

When I run the code, the window appears with the button, but clicking the button does not print “Button clicked!” in the console.

Could someone please help me understand what I am doing wrong? Is there something I am missing about the way signals and slots work in PyQt5?

I also check this: https://forum.pythonguis.com/t/help-with-pyqt5-bitmap-graphics-tutorialqlikview But I have not found any solution. Could anyone guide me about this. And your suggestion will be really grateful.

Thanks in advance! :innocent:

Respected community member :blush:

2

Hey Onikaa. Welcome to Python and PyQt.

It looks like you are attempting to follow a model-view-controller (MVC) architecture. Without seeing the tutorial you are following and the entirety of your code I can’t say for certain why _calculate isn’t working properly for you.

Admittedly, I am not very familiar with MVC programs so I won’t attempt to give you any advice there, maybe someone else will chime in for you on that. What I can do is point you down a simpler road for creating your first PyQt applications. What I’ve included for you below is a simple application with a single button. The app defines a class MainWindow which inherits the widget QMainWindow and explicitly defines the widgets to use in that window. You can use this boiler plate code as a foundation to flesh out your own creation.

Let me know if you have any questions about this code. Good luck!

-Trever

from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton
from PyQt5.QtCore import pyqtSlot  # Decorator to identify a function as a slot


class MainWindow(QMainWindow):
    """Extend the QMainWindow as the base for you app."""

    def __init__(self):
        """Initialize MainWindow."""
        # Run __init__ for QMainWindow
        super().__init__()

        # Give the window a title
        self.setWindowTitle("Push Button Example")

        # Resize the window so whole title is visible.
        self.resize(300, 50)

        # Define the button
        self.push_button = QPushButton("Push Button")

        # Assign the 'clicked' signal to a slot
        self.push_button.clicked.connect(self.button_clicked)

        # Make the button the central widget
        # Normally, the button would be added to a "central layout" which is
        # assigned to a central widget, but for brevity, I'm ommiting the
        # layout.
        self.setCentralWidget(self.push_button)

    # The decorator isn't stricly required, I just like using it. It comes in
    # really handy when you need to retrieve a value from the sending widget.
    @pyqtSlot()
    def button_clicked(self):
        """Slot to hold the instructions for when the button is clicked."""
        print("You clicked the button!")


# Define script if file is run directly. Ignored if MainWindow is called from
# another file.
if __name__ == "__main__":
    import sys

    # Instantiate application
    app = QApplication(sys.argv)

    # Instantiate and show MainWindow
    main_window = MainWindow()
    main_window.show()

    # Execute the application
    sys.exit(app.exec_())