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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Hi Chris,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I read that article and based on it I found out that I need to put processEvents() and I understand the logic in this.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Someone said:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt;font-family:"Segoe UI",sans-serif;color:#232629;background:#F9F8F6">In more recent QGIS versions the Python console no longer triggers this event loop, as it's often quite dangerous to execute the loop in the
middle of other running code.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt;font-family:"Segoe UI",sans-serif;color:#232629;background:#F9F8F6"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt;font-family:"Segoe UI",sans-serif;color:#232629;background:#F9F8F6">It seems somehow QGIS 2.18 was designed to send automatically updates to the GUIs when a loop is running and this capability was eliminated
in QGIS 3 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Anyway, thank you for your answer.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Marian<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> chris hermansen <clhermansen@gmail.com>
<br>
<b>Sent:</b> August 16, 2022 4:40 PM<br>
<b>To:</b> Tudorache, Marian <Marian.Tudorache@navcanada.ca><br>
<b>Cc:</b> qgis-user@lists.osgeo.org<br>
<b>Subject:</b> [EXT] Re: [Qgis-user] Event loop in QGIS3<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-line-height-alt:.75pt"><span style="font-size:1.0pt;color:white">Marian and list, On Tue, Aug 16, 2022 at 12: 02 PM Tudorache, Marian via Qgis-user <qgis-user@ lists. osgeo. org> wrote: Hello community, A while ago I sent a
question about a problem with QMessageBox and message bar does not get updated <o:p>
</o:p></span></p>
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<p class="MsoNormal" style="mso-line-height-alt:.75pt"><span style="font-size:1.0pt;color:white"><o:p></o:p></span></p>
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<p class="MsoNormal">Marian and list,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Tue, Aug 16, 2022 at 12:02 PM Tudorache, Marian via Qgis-user <<a href="mailto:qgis-user@lists.osgeo.org">qgis-user@lists.osgeo.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Hello community,<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">A while ago I sent a question about a problem with QMessageBox and message bar does not get updated during a long process.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">In my example I create a script like this.
<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">from qgis.PyQt import QtWidgets<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">message = "Wait to open the airspace project..."<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">msg = QtWidgets.QMessageBox()<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">msg.setText(message)<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">msg.show()<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">qgis.utils.iface.messageBar().pushMessage("Wait", message)<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">for i in range(1000):<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> print(i)<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">qgis.utils.iface.messageBar().pushMessage("Done", "The process is done")<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">msg.setText("The process is done")<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">msg.show()<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">qgis.utils.iface.messageBar().pushMessage("Done", "The process is done"))<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">When I run the scrip in QGIS 2.18 the QMessageBox displays first the message "Wait to open the airspace project...". The same message is pushed to messageBar.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Then during the loop it displays the variable i.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">At the end of the loop the QMessageBox displays the message "The process is done" which is also pushed to the messageBar.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">When I run the same scrip on QGIS 3 the QMessageBox is empty. The message "Wait to open the airspace project..." is not displayed by QMessageBox nor by messageBar.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">The print inside the loop displays the I and when the loop is done the QMessageBox displays the message "The process is done".<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">The messageBar displays also the message "The process is done". And after a while it displays the initial message "Wait to open the airspace project..."<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I modified the scrip by adding QApplication.processEvents() inside the loop and now everything is fine.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">It seems
<span style="font-size:11.5pt;font-family:"Segoe UI",sans-serif;color:#232629;background:#F9F8F6">
QGIS3 no longer triggers this event loop and I have to do this explicitly by calling
</span>processEvents from QApplication.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="color:black;background:yellow">Why QGIS 3 needs to call QApplication.processEvents() and QGIS 2 does not need?</span></b><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Marian, did you read this article?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><a href="https://urldefense.com/v3/__https:/doc.qt.io/qt-5/qcoreapplication.html*details__;Iw!!P0kg3YazkQ!CcSBA7taBRD4nM94gtxzazyv0U6cmASgYsOj82Fb8dTTzEuCUBZIOlqx018StM8IglMsIkz51FTlYFb0J6ClVfIwQbFuLA$">https://doc.qt.io/qt-5/qcoreapplication.html#details</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">There you will see this:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The event loop is started with a call to <a href="https://urldefense.com/v3/__https:/doc.qt.io/qt-5/qcoreapplication.html*exec__;Iw!!P0kg3YazkQ!CcSBA7taBRD4nM94gtxzazyv0U6cmASgYsOj82Fb8dTTzEuCUBZIOlqx018StM8IglMsIkz51FTlYFb0J6ClVfLZXx-a2Q$">
exec</a>(). Long-running operations can call <a href="https://urldefense.com/v3/__https:/doc.qt.io/qt-5/qcoreapplication.html*processEvents__;Iw!!P0kg3YazkQ!CcSBA7taBRD4nM94gtxzazyv0U6cmASgYsOj82Fb8dTTzEuCUBZIOlqx018StM8IglMsIkz51FTlYFb0J6ClVfI1OxPavQ$">
processEvents</a>() to keep the application responsive.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In your case, your "long-running operation" is your for loop. And it is not QGIS3 that has the responsibility to trigger processEvents() but your own long-running operation, at least the way I'm reading this.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">As to why QGIS 2 did not need this, I don't know.<br clear="all">
<o:p></o:p></p>
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<p class="MsoNormal"><br>
-- <o:p></o:p></p>
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<p class="MsoNormal">Chris Hermansen · clhermansen "at" gmail "dot" com<br>
<br>
C'est ma façon de parler.<o:p></o:p></p>
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