Issues when attaching and detaching external app from QDockWidget

Consider this little piece of code:

import subprocess
import win32gui
import win32con
import time
import sys
from PyQt5.Qt import *  # noqa


class Mcve(QMainWindow):

    def __init__(self, path_exe):
        super().__init__()

        menu = self.menuBar()

        attach_action = QAction('Attach', self)
        attach_action.triggered.connect(self.attach)
        menu.addAction(attach_action)

        detach_action = QAction('Detach', self)
        detach_action.triggered.connect(self.detach)
        menu.addAction(detach_action)

        self.dock = QDockWidget("Attach window", self)
        self.addDockWidget(Qt.RightDockWidgetArea, self.dock)

        p = subprocess.Popen(path_exe)
        time.sleep(0.5)  # Give enough time so FindWindowEx won't return 0
        self.hwnd = win32gui.FindWindowEx(0, 0, "CalcFrame", None)
        if self.hwnd == 0:
            raise Exception("Process not found")

    def detach(self):
        try:
            self._window.setParent(None)
            # win32gui.SetWindowLong(self.hwnd, win32con.GWL_EXSTYLE, self._style)
            self._window.show()
            self.dock.setWidget(None)
            self._widget = None
            self._window = None
        except Exception as e:
            import traceback
            traceback.print_exc()

    def attach(self):
        # self._style = win32gui.GetWindowLong(self.hwnd, win32con.GWL_EXSTYLE)
        self._window = QWindow.fromWinId(self.hwnd)
        self._widget = self.createWindowContainer(self._window)
        self.dock.setWidget(self._widget)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    w = Mcve("C:\\Windows\\system32\\calc.exe")
    w.show()
    sys.exit(app.exec_())

The goal here is to fix the code so the window attaching/detaching into a QDockWidget will be made properly. Right now, the code has 2 important issues.

Issue1

Style of the original window is screwed up:

a) Before attaching (the calculator has a menu bar)

b) When attached (the calculator menu bar is gone)

c) When detached (the menu bar hasn't been restored properly)

I've already tried using flags/setFlags qt functions or getWindowLong/setWindowLong but I haven't had luck with all my attempts

Issue2

If you have attached and detached the calculator to the mainwindow, and then you decide to close the mainwindow, you definitely want everything (pyqt process) to be closed and cleaned properly. Right now, that won't be the case, why?

In fact, when you've attached/detached the calculator to the mainwindow, the python process will hold and you'll need to force the termination of the process manually (i.e. ctrl+break conemu, ctrl+c cmd prompt)... which indicates the code is not doing things correctly when parenting/deparenting

Additional notes:

• http://doc.qt.io/qt-5/qwindow.html#fromWinId
• http://doc.qt.io/qt-5/qwidget.html#createWindowContainer
• In the above minimal code I'm spawning calc.exe as a child process but you can assume calc.exe is an existing non-child process spawned by let's say explorer.exe

Solution 1:

I found part of the issue wrt to closing. So when you are creating the self._window in the attach function and you close the MainWindow, that other window (thread) is sitting around still. So if you add a self._window = None in the __init__ function and add a __del__ function as below, that part is fixed. Still not sure about the lack of menu. I'd also recommend holding onto the subprocess handle with self.__p instead of just letting that go. Include that in the __del__ as well.

    def __del__(self):
        self.__p.terminate()
        if self._window:
            print('terminating window')
            self._window.close

Probably better yet would be to include a closeEvent

    def closeEvent(self, event):
        print('Closing time')
        self.__p.terminate()
        if self._window is not None:
            print('terminating window')
            self._window.close