[PyQt] Non-Modal Dialog
Kyle Altendorf
sda at fstab.net
Wed Oct 9 02:48:23 BST 2019
On October 7, 2019 6:08:29 PM EDT, Dennis Jensen <djensen at pgcontrols.com> wrote:
>Actually QPixMap is not only not Thread safe per-sae but elements of it
>
>are Thread prohibited as are all QtWidgets
I know you shouldn't access GUI elements from other threads. I wasn't aware of this. Do you have a reference?
>On 10/6/2019 2:59 PM, Maurizio Berti wrote:
>> After some tests, I found that the problem is not about modal windows
>
>> at all.
>> If you check carefully, even after the QThread.sleep, the dialog
>> interaction is blocked until the image is saved.
>>
>> It turns out that the issue here is that QPixmap is *not* thread safe
>
>> (at least, not in all platforms).
>> It does not seem to be any official documentation about this, but I
>> found some information on this thread:
>>
>https://forum.qt.io/topic/52397/not-safe-to-use-qpixmap-outside-the-gui-thread/4
>>
>> A simple solution is to convert the pixmap to a QImage and use its
>> save() function, which seems to be thread safe and doesn't block the
>GUI:
>>
>> WIN.pixmap.toImage().save('/tmp/nonmodal_test.png')
>>
>> A couple of slightly unrelated suggestions, if I may.
>> - You don't need to return every function if the returned value is
>not
>> required, as Python implicitly returns None if no explicit return
>exists
>> - Avoid using object names that already are existing properties or
>> methods (like self.thread)
>> - You can connect the finished signal directly to the close (or,
>> better, accept) slot of the popup and delete the thread itelf:
>>
>> class WaitMessage(QMessageBox):
>> ''' a message box that can't be closed by the user
>> '''
>> def __init__(self, parent):
>> super(WaitMessage, self).__init__(QMessageBox.Information, 'Wait',
>> 'This is a test, please wait', parent=parent)
>> # setting NoButton in the constructor won't be enough, it
>must
>> be set explicitly
>> # in this way the Escape key won't hide the dialog
>> self.setStandardButtons(QMessageBox.NoButton)
>>
>> def closeEvent(self, event):
>> # ignore any attempt to close the dialog via the title bar
>buttoni
>> event.ignore()
>>
>> class WinMain(QMainWindow):
>> # ...
>> def test_part_1(self):
>> popup = WaitMessage(self)
>> worker = ThdWorker(self)
>> worker.started.connect(popup.exec_)
>> worker.finished.connect(worker.deleteLater)
>> worker.finished.connect(popup.deleteLater)
>> worker.start()
>>
>> With this approach you won't need another function to delete the
>popup
>> nor the thread, as they will be deleted in Qt "scope" with
>> deleteLater, and will be deleted by python followingly, since they're
>
>> not instance attributes.
>> Just ensure that both the popup and the worker have a parent,
>> otherwise they will be garbage collected as soon as the function
>returns.
>>
>> Cheers,
>> Maurizio
>>
>>
>> Il giorno dom 6 ott 2019 alle ore 18:20 Chuck Rhode
>> <CRhode at lacusveris.com <mailto:CRhode at lacusveris.com>> ha scritto:
>>
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> In the deep past, I've worked with VB, Tk, Pascal Delphi, and
>Gtk. I
>> seem to recall that all had non-modal dialog boxes for situations
>> where
>> you wanted to inform the user through the user interface that a
>> long-running task was in progress. Is this not done anymore?
>>
>> I assume there are still long running tasks such as QPixmap
>*save*s.
>>
>> These tasks cannot emit progress signals for powering a progress
>bar.
>> What alternatives are there?
>>
>> I can't get a cursor change to show up.
>>
>> Does one nowadays throw up a semitransparent overlay with a
>spinner?
>> That is not so simple or informative as a non-modal dialog, I
>think.
>>
>> I've pored over Stackoverflow posts about Qt from the last
>decade, and
>> I don't see a lot that I can use. Most say its as simple as
>> QMessageBox *open* instead of *exec_*, but this has not been my
>> experience with PyQt. Here is code that works, however:
>>
>> #!/usr/bin/python
>> # -*- coding: utf-8 -*-
>>
>> # nonmodal_example.py
>> # 2019 Oct 06 . ccr
>>
>> """Demonstrate how to show a non-modal dialog box before starting
>a
>> long-running task.
>>
>> """
>>
>> from __future__ import division
>> import sys
>> from PyQt5.QtWidgets import (
>> QApplication,
>> QMainWindow,
>> QWidget,
>> QGridLayout,
>> QPushButton,
>> QMessageBox,
>> )
>> from PyQt5.QtGui import (
>> QPixmap,
>> QTransform,
>> )
>> from PyQt5.QtCore import(
>> QThread,
>> )
>>
>> ZERO = 0
>> SPACE = ' '
>> NULL = ''
>> NUL = '\x00'
>> NA = -1
>>
>>
>> class ThdWorker(QThread):
>>
>> """An (arbitrarily) long-running task.
>>
>> """
>>
>> def run(self):
>> QThread.sleep(1)
>> WIN.pixmap.save('/tmp/nonmodal_test.png')
>> return
>>
>>
>> class WinMain(QMainWindow):
>>
>> """The (trivial) main window of the graphical user interface.
>>
>> """
>>
>> def __init__(self):
>> super(WinMain, self).__init__()
>> self.resize(800, 600)
>> self.central_widget = QWidget(self)
>> self.setCentralWidget(self.central_widget)
>> self.layout = QGridLayout()
>> self.central_widget.setLayout(self.layout)
>> self.btn_run = QPushButton('Run Next Test Scenario',
>> self.central_widget)
>> self.btn_run.setMaximumSize(200, 30)
>> self.btn_run.clicked.connect(self.test_part_1)
>> self.layout.addWidget(self.btn_run)
>> figure = QPixmap()
>> result =
>>
>figure.load('/usr/share/qt5/doc/qtdesigner/images/designer-screenshot.png')
>> if result:
>> pass
>> else:
>> raise NotImplementedError
>> transformation = QTransform()
>> transformation.scale(5.0, 5.0)
>> self.pixmap = figure.transformed(transformation)
>> return
>>
>> def test_part_1(self):
>>
>> """Fork a thread.
>>
>> """
>>
>> self.popup = QMessageBox(QMessageBox.Information, None,
>> 'This is a test. Please wait.')
>> self.popup.show()
>> self.thread = ThdWorker(self)
>> self.thread.finished.connect(self.test_part_2)
>> self.thread.start()
>> return
>>
>> def test_part_2(self):
>> self.popup.close()
>> del self.popup
>> del self.thread
>> return
>>
>>
>> if __name__ == "__main__":
>> APP = QApplication(sys.argv)
>> WIN = WinMain()
>> WIN.show()
>> result = APP.exec_()
>> sys.exit(result)
>>
>>
>> # Fin
>>
>> What really gripes me about this example, despite the fact that
>it
>> works for me, is the sleep at the beginning of the thread that
>starts
>> the long running thread. The sleep is essential. Although the
>> QMessageBox *show* paints its frame, it doesn't have time to
>paint its
>> contents unless the thread pauses before it even gets going.
>>
>> There HAS TO BE a more elegant way to allow non-modal dialogs to
>paint
>> completely. I've tried lots of different Stackoverflow
>> recommendations, and nothing works. I have a more complete (and
>> considerably longer) test suite ready to show you that is
>> available upon
>> request.
>>
>> - --
>> .. Be Seeing You,
>> .. Chuck Rhode, Sheboygan, WI, USA
>> .. Weather: http://LacusVeris.com/WX
>> .. 55° — Wind WSW 10 mph
>>
>> -----BEGIN PGP SIGNATURE-----
>> Version: GnuPG v2
>>
>> iEYEARECAAYFAl2aE+IACgkQYNv8YqSjllJHuwCfW+tQv04X3s8e6jE5gWZPqbeN
>> kZgAn2nbhXFERp5rmIcEuO6yEvC8+HVF
>> =bE0d
>> -----END PGP SIGNATURE-----
>> _______________________________________________
>> PyQt mailing list PyQt at riverbankcomputing.com
>> <mailto:PyQt at riverbankcomputing.com>
>> https://www.riverbankcomputing.com/mailman/listinfo/pyqt
>>
>>
>>
>> --
>> È difficile avere una convinzione precisa quando si parla delle
>> ragioni del cuore. - "Sostiene Pereira", Antonio Tabucchi
>> http://www.jidesk.net
>>
>> _______________________________________________
>> PyQt mailing list PyQt at riverbankcomputing.com
>> https://www.riverbankcomputing.com/mailman/listinfo/pyqt
More information about the PyQt
mailing list