Question

In the attached example script, why won’t the MyDialog instance show properly when I set MyDialog’s parent to self on line 20 instead of leaving it blank? First I thought the shortcut had stopped working somehow, but obviously that’s not the case.

In this case it doesn’t really make any difference whether the parent is set, but in my real case I need the parent to be set.

Am I missing something obvious here?

import sys

from PyQt4.QtCore import *
from PyQt4.QtGui import *

class MyDialog(QDialog):
    def __init__(self, parent=None):
        QDialog.__init__(self, parent)
        self.setWindowFlags(Qt.FramelessWindowHint)
        self.setFocusPolicy(Qt.StrongFocus)
        label = QLabel(self)
        label.setText("World")
        hbox = QHBoxLayout()
        hbox.addWidget(label)
        self.setLayout(hbox)

class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        QMainWindow.__init__(self, parent)
        self.my_dialog = MyDialog()
        #self.my_dialog = MyDialog(self)
        label = QLabel(self)
        label.setText("Hello")
        self.setCentralWidget(label)
        shortcut = QShortcut(QKeySequence(Qt.Key_Tab), self, self.show_my_dialog)
        shortcut.setContext(Qt.ApplicationShortcut)
        self.show()
    def show_my_dialog(self):
        md = self.my_dialog
        if md.isVisible():
            md.hide()
            print 'hide'
        else:
            md.show()
            print 'show'

def main():
    app = QApplication([])
    main_window = MainWindow()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

Answer 1

On my machine (Kubuntu 11.10) it’s working.
If Dialog’s parent is None – it opens another frameless window, and i have two entries in taskbar. If i close the main window, dialog remains.

If you are using Windows – the behavior you described might be related to it. Maybe the window is shown, it’s just behind other windows?

If Dialog’s parent is the main window – the frameless dialog is shown inside the main window – in the top left corner near the label.

You might be interested in this info:

A dialog window is a top-level window mostly used for short-term tasks
and brief communications with the user. QDialogs may be modal or
modeless. QDialogs can provide a return value, and they can have
default buttons. QDialogs can also have a QSizeGrip in their
lower-right corner, using setSizeGripEnabled().

Note that QDialog (an
any other widget that has type Qt::Dialog) uses the parent widget
slightly differently from other classes in Qt. A dialog is always a
top-level widget, but if it has a parent, its default location is
centered on top of the parent’s top-level widget (if it is not
top-level itself). It will also share the parent’s taskbar entry.

Use
the overload of the QWidget::setParent() function to change the
ownership of a QDialog widget. This function allows you to explicitly
set the window flags of the reparented widget; using the overloaded
function will clear the window flags specifying the window-system
properties for the widget (in particular it will reset the Qt::Dialog
flag).