[PyQt] Non-Modal Dialog

[Dennis Jensen]

Hey Chuck if you would like to drop me a line on Discord `DenniO#8137` 
we can discuss this item -- from what I understand its a combination of 
the GIL and how threads and multi-processes work -- which I can go into 
more depth with you off list

On 10/6/2019 11:18 AM, Chuck Rhode wrote:
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> 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
>
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