When a function is called - a file is tested for existence. This checksum pushes a messageBar() object for both circumstances (True/False), yet the actual bar does not display in MapCanvas until after the subsequent exec_() is called and finished running.

def callUtherPendragonsSon(self):
    holyGrailFile = 'C:\ALongWayFrom\camelot.csv'
    if os.path.exists(holyGrailFile):
        self.iface.messageBar().pushMessage("Notice", "You will need many coconuts...",\
                                            level=QgsMessageBar.INFO, duration=3)
        beginTheJourney = gatherProvisionsAndMen()
        self.iface.messageBar().pushMessage("Warning", "There is no grail :( ",\
                                            level=QgsMessageBar.CRITICAL, duration=3)

Is there a means to assure the message bar is pushed prior to calling the exec_() ?


As it turns out, a command in the external Ui gatherProvisionsAndMen()'s init is causing the trouble. It is a data-thirsty function call, and seems to supersede the messagebar (even though it is executed thereafter). The messageBar itself is intended to preliminarily notify the user of this nested 'lengthy process' - but it seems such a notice needs to take place in another manner...

Perhaps I hold a misunderstanding in the logistics of programming but,

wouldn't the call to push a QgsMessageBar() need to complete before moving forward and executing the external Ui?

  • Do you mean you only see the bar after you've closed the dialog? Cannot replicate the issue. Feb 17, 2015 at 18:42
  • The bar is only displayed after the external Ui-dialog has passed the *.show() command. e.g.-both the messageBar and Ui appear simultaneously, rather then (as intended) the former before the later.
    – Katalpa
    Feb 17, 2015 at 18:44
  • Still cannot replicate it. In my test plugin, I added a for loop in between to delay the show() call, however, the message appears immediately after it's called. Feb 17, 2015 at 18:47
  • I cannot seem to find the success you mention. Is it possible that my QgisVer (2.7-Dev) is @ cause?
    – Katalpa
    Feb 17, 2015 at 18:52
  • 1
    That could be the case. Perhaps you could try with a simple version and see if it gets better, i.e., try to isolate the problem. Feb 17, 2015 at 19:05

2 Answers 2


To solve this problem, just say to the main window to repaint itself after pushing your message with the repaint function :

 self.iface.messageBar().pushMessage("Please wait...", level=QgsMessageBar.INFO, duration=0)
 # Do something that takes time

Just put dummy print 'xxx' statement immediately after self.iface.messageBar().pushMessage call.

  • I have found that if the Python plugin console is not open during such scripted prints - errors arise. Maybe due to the version I have implemented?
    – Katalpa
    Apr 24, 2015 at 17:19
  • Describe an error message please.
    – Artur Lill
    Apr 25, 2015 at 9:38
  • " File "C:/PROGRA~1/QGISWI~1/apps/qgis/./python/plugins\GraphicGroundwater\loadParticleTracks.py", line 265, in constructShapefile print newPathGroups IOError: [Errno 9] Bad file descriptor"
    – Katalpa
    Apr 25, 2015 at 18:06
  • You are right about Python plugin console: my solution works only if this console is open.
    – Artur Lill
    Apr 27, 2015 at 14:00
  • To debug an error just try to disable/enable installed plugin again... not sure what is the real cause of this error.
    – Artur Lill
    Apr 27, 2015 at 14:08

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