Adding QWidget in QMainWindow which already has a central widget in PyQt

Question

I am developing a GUI app in PyQt.

For the buttons, I have used QWidget and for a QSqlTable I have used a QMainWindow.

I know I can add QWidget by adding setCentralwidget in QMainWindow. But in order to show the Table, I need the table to be central widget.

Individually both work, but I am unable to have both at the same time.

My code is given below:

import sys
from PyQt5 import QtCore, QtWidgets
from PyQt5.QtWidgets import QVBoxLayout, QGroupBox, QGridLayout, QPushButton,QLabel.  
from PyQt5.QtGui import QPixmap
from PyQt5 import QtGui
from gwWindow import groundwaterWindow
from swWindow import surfacewaterWindow
from kwWindow import karstwaterWindow
from PyQt5.QtCore import Qt, QModelIndex
from PyQt5.QtSql import QSqlDatabase, QSqlTableModel, QSqlQuery
from PyQt5.QtWidgets import (QApplication, QMainWindow, QMessageBox, QTableView,     QPushButton, QGridLayout, QGroupBox, QVBoxLayout)
from PyQt5 import QtCore
from PyQt5.QtCore import pyqtSignal


class MainWindow(QtWidgets.QWidget):
    def __init__(self):
        QtWidgets.QWidget.__init__(self)
        self.title = "PPCP Selection"
        self.top = 100

        self.left = 100
        self.width = 1200
        self.height = 1200


        self.InitWindow()

    def InitWindow(self):
        self.setWindowTitle(self.title)
        self.setGeometry(self.top, self.left, self.width, self.height)

        self.createLayout()

        vBoxLayout = QVBoxLayout()

        vBoxLayout.addWidget(self.groupBox1)
        # vBoxLayout.addWidget(self.groupBox2)
        self.setLayout(vBoxLayout)
        # self.showMaximized()

    def createLayout(self):
        self.groupBox1 = QGroupBox("PPCP Selection")
        self.groupBox1.setFont(QtGui.QFont("Arial", 30))
        gridLayout = QGridLayout()
        gridLayout.setRowStretch(2, 2)


        self.button1 = QPushButton("Evaluate")
        gridLayout.addWidget(self.button1, 1, 0, 1, 1)
        #self.button1.clicked.connect(self.switch1)
        gridLayout.addWidget(self.button1)
        self.button1.setFocusPolicy(QtCore.Qt.NoFocus)

        self.groupBox1.setLayout(gridLayout)


class RealMainWindow(QMainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setWindowTitle("QTableView Example")
        self.resize(415, 200)
        # Set up the model
        self.model = TableModel(self)
        self.model.setTable("Table2")
        self.model.setEditStrategy(QSqlTableModel.OnFieldChange)
        #self.model.setHeaderData(0, Qt.Horizontal, "ID")


        self.model.select()
        # Set up the view
        self.view = QTableView()
        self.view.setModel(self.model)
        #self.view.resizeColumnsToContents()

        self.another = MainWindow()

        # I want both of the following


        # self.setCentralWidget(self.view)
        # self.setCentralWidget(self.another)

    def secondWindow(self):
        self.another = MainWindow()
        self.another.show()



class TableModel(QSqlTableModel):
    def __init__(self, *args, **kwargs):
        QSqlTableModel.__init__(self, *args, **kwargs)
        self.checkeable_data = {}

    def flags(self, index):
        fl = QSqlTableModel.flags(self, index)
        if index.column() == 0:
            fl |= Qt.ItemIsUserCheckable
        return fl

    def data(self, index, role=Qt.DisplayRole):
        if role == Qt.CheckStateRole and (
            self.flags(index) & Qt.ItemIsUserCheckable != Qt.NoItemFlags
        ):
            if index.row() not in self.checkeable_data.keys():
                self.setData(index, Qt.Unchecked, Qt.CheckStateRole)
            return self.checkeable_data[index.row()]
        else:
            return QSqlTableModel.data(self, index, role)

    def setData(self, index, value, role=Qt.EditRole):
        if role == Qt.CheckStateRole and (
            self.flags(index) & Qt.ItemIsUserCheckable != Qt.NoItemFlags
         ):
            self.checkeable_data[index.row()] = value
            self.dataChanged.emit(index, index, (role,))
            return True
        return QSqlTableModel.setData(self, index, value, role)


def createConnection():

    con = QSqlDatabase.addDatabase("QSQLITE")
    con.setDatabaseName("ppcp_database.db")
    if not con.open():
        QMessageBox.critical(
            None,
            "QTableView Example - Error!",
            "Database Error: %s" % con.lastError().databaseText(),
        )
        return False
    return True

app = QApplication(sys.argv)
if not createConnection():
  sys.exit(1)
win = RealMainWindow()
win.show()
sys.exit(app.exec_())

Answer 1

Use a Qt layout:

class RealMainWindow(QMainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setWindowTitle("QTableView Example")
        self.resize(415, 200)

        # Set up the model
        self.model = TableModel(self)
        self.model.setTable("Table2")
        self.model.setEditStrategy(QSqlTableModel.OnFieldChange)
        self.model.select()

        self.view = QTableView()
        self.view.setModel(self.model)

        self.another = MainWindow()

        central_widget = QWidget()
        self.setCentralWidget(central_widget)
        lay = QVBoxLayout(central_widget)
        lay.addWidget(self.view)
        lay.addWidget(self.another)