Empty QMainWindow, PyQt

Question

I have two QMainWindows, I'm trying to call one from the other one. The window opens but , it is empty and does not respond until the parent window is closed.

My Code:

from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    _fromUtf8 = lambda s: s

class Ui_MainWindow(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self,None)

    def setupUi(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(184, 165)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.pushButton = QtGui.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(40, 40, 75, 23))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 184, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QObject.connect(self.pushButton , QtCore.SIGNAL("clicked()"),self.gone)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))
        self.pushButton.setText(QtGui.QApplication.translate("MainWindow", "PushButton", None, QtGui.QApplication.UnicodeUTF8))

    def gone(self):
        mainwindow = QtGui.QMainWindow()
        self.mw2 = Ui_MainWindow1()
        self.mw2.setupUi(mainwindow)
        self.mw2.show()

class Ui_MainWindow1(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self,None)

    def setupUi(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(170, 175)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.label = QtGui.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(40, 60, 101, 16))
        self.label.setObjectName(_fromUtf8("label"))
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 170, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))
        self.label.setText(QtGui.QApplication.translate("MainWindow", "This is second", None, QtGui.QApplication.UnicodeUTF8))

def startmain():
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow() # <-- Instantiate QMainWindow object.
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    app.exec_()

if __name__ == "__main__":
    import sys
    startmain()

Answer 1

I don't understand why you are creating QMainWindow objects when your Ui_MainWindow and Ui_MainWindow1 classes are subclasses of QMainWindow. Basically, you have four main windows, when you only need two.

Instead of creating QMainWindows called MainWindow, and setting things up in them, set up each window in itself by using self instead of MainWindow. The following appears to work for me, in that the first window has a button, and clicking it opens the second with a label in it:

from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    _fromUtf8 = lambda s: s

class Ui_MainWindow(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self,None)

    def setupUi(self):
        self.setObjectName(_fromUtf8("self"))
        self.resize(184, 165)
        self.centralwidget = QtGui.QWidget(self)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.pushButton = QtGui.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(40, 40, 75, 23))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        self.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(self)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 184, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        self.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(self)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        self.setStatusBar(self.statusbar)

        self.retranslateUi()
        QtCore.QObject.connect(self.pushButton , QtCore.SIGNAL("clicked()"),self.gone)
        QtCore.QMetaObject.connectSlotsByName(self)

    def retranslateUi(self):
        self.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))
        self.pushButton.setText(QtGui.QApplication.translate("MainWindow", "PushButton", None, QtGui.QApplication.UnicodeUTF8))

    def gone(self):
        self.mw2 = Ui_MainWindow1()
        self.mw2.setupUi()
        self.mw2.show()

class Ui_MainWindow1(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self,None)

    def setupUi(self):
        self.setObjectName(_fromUtf8("self"))
        self.resize(170, 175)
        self.centralwidget = QtGui.QWidget(self)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.label = QtGui.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(40, 60, 101, 16))
        self.label.setObjectName(_fromUtf8("label"))
        self.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(self)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 170, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        self.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(self)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        self.setStatusBar(self.statusbar)

        self.retranslateUi()
        QtCore.QMetaObject.connectSlotsByName(self)

    def retranslateUi(self):
        self.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))
        self.label.setText(QtGui.QApplication.translate("MainWindow", "This is second", None, QtGui.QApplication.UnicodeUTF8))

def startmain():
    app = QtGui.QApplication(sys.argv)
    ui = Ui_MainWindow()
    ui.setupUi()
    ui.show()
    app.exec_()

if __name__ == "__main__":
    import sys
    startmain()