PYQT5 QMainWindow setCentralWidget consisting of multiple box layouts

Question

For a project in programming class we need to develop an application and have to use PYQT5 for the GUI.

I have a class based on QMainWindow. There are some lines of code I don't quite understand. Below is the initialization:

# Snippet 1
class ApplicationWindow(QtWidgets.QMainWindow):
def __init__(self):
    QtWidgets.QMainWindow.__init__(self)
    # self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
    self.setWindowTitle("Main Window")

Then, the following variables/GUI elements are defined:

    # Snippet 2
    self.main_widget = QtWidgets.QWidget(self)

    l = QtWidgets.QVBoxLayout(self.main_widget)
    sc = MyStaticMplCanvas(width=5, height=4, dpi=100) # just some graph
    dc = MyDynamicMplCanvas(width=5, height=4, dpi=100) # another graph
    l.addWidget(sc)
    l.addWidget(dc)

Then, I tried to add a horizontal box layout with the following content:

   # Snippet 3
    x = QtWidgets.QHBoxLayout(self.main_widget) # new
    b1 = QtWidgets.QPushButton("Test1") # new
    b2 = QtWidgets.QPushButton("Test2") # new
    x.addWidget(p1) # new
    x.addWidget(p2) # new

Lastly, the central widget is generated:

    # Snippet 4
    self.main_widget.setFocus()
    self.setCentralWidget(self.main_widget)

The program itself produces no error and works properly. But only the two graphs in snippet 2 are displayed in the window. If you delete

self.main_widget

from

l = QtWidgets.QVBoxLayout(self.main_widget)

and leave the parenthesis empty, only the buttons in snippet 3 are displayed.

What is the meaning behind the following assignment?

self.main_widget = QtWidgets.QWidget(self)

Are you able to combine the vertical and horizontal box layout into a single one and therefore display the two buttons as well as the two graphs as the central widget? This was my original plan and I tried some things with the addLayout() and setLayout() options and wanted to add these layouts to the setCentralWidget() but was not successful.

Do you have an idea on how to display a combination of multliple box layouts as the central widget in a class based on QMainWindow?

Thank you very much. :)

score 4 · Accepted Answer · answered Apr 15 '19 at 16:33

You can nest layouts using addLayout() on a layout; the inner layout then becomes a child of the layout it is inserted into.

class ApplicationWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()

        # self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
        self.setWindowTitle("Main Window")

        self.main_widget = QtWidgets.QWidget(self)
        self.main_widget.setFocus()
        self.setCentralWidget(self.main_widget)

        l = QtWidgets.QVBoxLayout(self.main_widget)
        sc = MyStaticMplCanvas(width=5, height=4, dpi=100)  # just some graph
        dc = MyDynamicMplCanvas(width=5, height=4, dpi=100) # another graph
        l.addWidget(sc)
        l.addWidget(dc)        

       # Snippet 3
        x = QtWidgets.QHBoxLayout()         # self.main_widget) # new
        b1 = QtWidgets.QPushButton("Test1") # new
        b2 = QtWidgets.QPushButton("Test2") # new
        x.addWidget(b1)                     # new   + b1
        x.addWidget(b2)                     # new   + b2

        l.addLayout(x)                                                  # <----

if __name__ == "__main__": 
    import sys 
    app = QtWidgets.QApplication(sys.argv) 
    MainWindow = ApplicationWindow() 
    MainWindow.show() 
    sys.exit(app.exec_())

Amazing! This is exactly what I was looking for. Thank you very much! — Pascal, Apr 15 '19 at 19:08

PYQT5 QMainWindow setCentralWidget consisting of multiple box layouts

1 Answers1