[Qgis-user] Event loop in QGIS3

[Patrick Dunford]

Thanks for this question. I had the same issue in my code, but running a 
console script in the Qgis application, printing to the console output 
would achieve the same thing. Is this applicable to scripts that run in 
the console?

On 17/08/22 07:02, Tudorache, Marian via Qgis-user wrote:
>
> Hello community,
>
> A while ago I sent a question about a problem with QMessageBox and 
> message bar does not get updated during a long process.
>
> In my example I create a script like this.
>
> from qgis.PyQt import QtWidgets
>
> message = "Wait to open the airspace project..."
>
> msg = QtWidgets.QMessageBox()
>
> msg.setText(message)
>
> msg.show()
>
> qgis.utils.iface.messageBar().pushMessage("Wait", message)
>
> for i in range(1000):
>
>     print(i)
>
> qgis.utils.iface.messageBar().pushMessage("Done", "The process is done")
>
> msg.setText("The process is done")
>
> msg.show()
>
> qgis.utils.iface.messageBar().pushMessage("Done", "The process is done"))
>
> 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.
>
> Then during the loop it displays the variable i.
>
> At the end of the loop the QMessageBox displays the message "The 
> process is done" which is also pushed to the messageBar.
>
> 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.
>
> The print inside the loop displays the I and when the loop is done the 
> QMessageBox displays the message "The process is done".
>
> 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..."
>
> I modified the scrip by adding QApplication.processEvents() inside the 
> loop and now everything is fine.
>
> It seems QGIS3 no longer triggers this event loop and I have to do 
> this explicitly by calling processEvents from QApplication.
>
> *Why QGIS 3 needs to call QApplication.processEvents() and QGIS 2 does 
> not need?*
>
> Thank you,
>
> Marian
>
>
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