How to avoid the child QMainWindow disappearing? - pyqt

Question

When I click the button, "ChildWindow" will flash and disappear. Then If I add the function exec_(), it will report an "AttributeError" because "QMainWindow" don't have this attribute.
How to modify the function "showChildWindow" so that it can work well? Thank you.
import sys
from PyQt4 import QtCore, QtGui
class MainWindow(QtGui.QMainWindow):
def __init__(self, parent=None):
QtGui.QWidget.__init__(self, parent)
self.setWindowTitle("MainWindow Window!")
self.setGeometry(400, 400, 100, 100)
self.centerWidget = QtGui.QWidget()
self.setCentralWidget(self.centerWidget)
self.pushButton = QtGui.QPushButton("&Button")
layout = QtGui.QVBoxLayout()
layout.addWidget(self.pushButton)
self.centerWidget.setLayout(layout)
class ChildWindow(QtGui.QMainWindow):
def __init__(self, parent=None):
QtGui.QWidget.__init__(self, parent)
self.setWindowTitle("Child Window!")
def showChildWindow():
mw = MainWindow()
child_win = ChildWindow(mw)
child_win.show()
#child_win.exec_() #AttributeError: 'ChildWindow' object has no attribute 'exec_'
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
myapp = MainWindow()
myapp.show()
QtCore.QObject.connect(myapp.pushButton,QtCore.SIGNAL("clicked()"),showChildWindow)
sys.exit(app.exec_())
This program can work well.
import sys
from PyQt4 import QtCore, QtGui
class MainWindow(QtGui.QMainWindow):
def __init__(self, parent=None):
QtGui.QWidget.__init__(self, parent)
self.setWindowTitle("MainWindow Window!")
self.setGeometry(400, 400, 100, 100)
self.centerWidget = QtGui.QWidget()
self.setCentralWidget(self.centerWidget)
pushButton = QtGui.QPushButton("&Button")
layout = QtGui.QVBoxLayout()
layout.addWidget(pushButton)
self.centerWidget.setLayout(layout)
QtCore.QObject.connect(pushButton,QtCore.SIGNAL("clicked()"),self.showChildWindow)
def showChildWindow(self):
self.child_win = ChildWindow(self)
self.child_win.show()
class ChildWindow(QtGui.QMainWindow):
def __init__(self, parent=None):
QtGui.QWidget.__init__(self, parent)
self.setWindowTitle("Child Window!")
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
myapp = MainWindow()
myapp.show()
sys.exit(app.exec_())

Answer 1

The real question appears to be: how do I access the main-window from other modules in my application?
My preferred general solution to this problem is to sub-class QApplication and add a simple accessor method, like this:
class Application(QtGui.QApplication):
def __init__(self):
QtGui.QApplication.__init__(self, sys.argv)
self._window = None
def window(self):
if self._window is None:
self._window = MainWindow()
return self._window
if __name__ == "__main__":
app = QtGui.qApp = Application()
app.window().show()
sys.exit(app.exec_())
With that in place, you can easily get access the methods of the main-window in other modules like this:
from PyQt4 import QtGui
QtGui.qApp.window().showChildWindow()

Answer 2

I had the same problem. The child QMainWindow would randomly disappear while interacting with the parent window.
This is the bad source code that causes this problem:
def showChildWindow(self):
child_win = ChildWindow()
child_win.show()
This is the good source code that fixes the problem:
def showChildWindow(self):
child_win = ChildWindow(self)
child_win.show()
When you instantiate the child window, make sure you pass the parent self.