update text in a Qt interface from method not in main script

Question

I want to call in my main program a method ExecuteM where in a while loop a text in my interface in Qt (call result), done with Qt creator will be update for each iteration.

class Machine():
    def __init__(self, result):
        self.result=result

    def ExecuteM(self, Var1, Var2):
        while Var1 != 'stop':
            Var2 = Var2 + 3
            self.result.setText(newResult())
            sleep(0.5)

then in my main script:

def main(self):
    self.TM=Machine(self.result)
    self.TM.ExecuteM(var1, var2)

but it does not work the text does not update at each iteration, why ?

score 2 · Accepted Answer · edited May 23 '17 at 12:08

2

If you execute a while-loop in the main thread, it will block the gui. All events will be queued until the while-loop terminates and control can return to the event-loop. So you either have to move the blocking while-loop into a separate thread, or periodically force the event-loop to process the pending events. In your example, it should probably be possible to achieve the latter like this:

    def ExecuteM(self, Var1, Var2):
        while Var1 != 'stop':
            Var2 = Var2 + 3
            self.result.setText(newResult())
            QApplication.processEvents()
            sleep(0.5)

But that's just a short-term solution. It would probably be better to use a worker thread and send a custom signal back to the main thread.

edited May 23 '17 at 12:08

Community

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1

answered Dec 12 '16 at 17:22

ekhumoro

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thanks, I think i start to understand the idea. But when I try your short-term solution I get : `QApplication.processEvents() NameError: global name 'QApplication' is not defined` ...? – Dadep Dec 12 '16 at 17:38
@Dadep. You need to import it - or maybe use `QtGui.QApplication` (or `QtWidgets.QApplication` for PyQt5). – ekhumoro Dec 12 '16 at 17:49
It was a problem of `from PyQt4.QtCore import *, from PyQt4.QtGui import * ` ... Ah yes exactly ! (I was writing comment at the same time) Thanks – Dadep Dec 12 '16 at 17:50

update text in a Qt interface from method not in main script

1 Answers1