[PyQt] PyQt (QtGui.QTableWidget) problem using threads

[Brent Villalobos]

You can only do GUI operations in the main thread.  I would emit signals 
from your worker thread that are connected to operations in your main 
threads that do the actual gui manipulation.
-Brent

Ole Streicher wrote:
> Hi,
>
> When I try to update a table from another thread, my program crashes or
> gives really unexpected results.
>
> Here is some example code:
> ---------------------------------8<--------------------------------------
> import threading
> import sys
> import time
>
> from PyQt4 import QtGui, QtCore
>
> app = QtGui.QApplication(sys.argv)
>
> main = QtGui.QMainWindow()
> table = QtGui.QTableWidget(2, 2, main)
> main.setCentralWidget(table)
>
> class MyThread(threading.Thread):
>     def run(self):
>         time.sleep(3)
>         table.insertRow(2)
>         table.setCellWidget(2, 0, QtGui.QLabel('Hallo Welt'))
>         
> MyThread().start()
>
> main.show()
> app.exec_()
> ---------------------------------8<--------------------------------------
>
> The sleep() function just simulates some calculation.
> When I start the program, it always shows warnings like 
>
> QObject::setParent: Cannot set parent, new parent is in a different thread
> QPixmap: It is not safe to use pixmaps outside the GUI thread
> QObject::installEventFilter(): Cannot filter events for objects in a different thread.
>
> QObject::installEventFilter(): Cannot filter events for objects in a different thread.
> QObject::installEventFilter(): Cannot filter events for objects in a different thread.
> QCoreApplication::sendPostedEvents: Cannot send posted events for objects in another thread
> QCoreApplication::sendPostedEvents: Cannot send posted events for objects in another thread
>
> Sometimes it shows the QLabel in an extra window which re-openes when I
> try to close it. Sometimes this program crashes with the additional
> printout
>
> python: ../../src/xcb_io.c:176: process_responses: Assertion `!(req && current_request && !(((long) (req->sequence) - (long) (current_request)) <= 0))' failed.
> Aborted
>
> or 
>
> X Error: BadGC (invalid GC parameter) 13
>   Major opcode: 56 (X_ChangeGC)
>   Resource id:  0x2803500
> table.py: Fatal IO error: client killed
>
> What is wrong with my code and how can I add a table row and fill it
> with a QWidget from another thread? I already tried to set the parent of
> the QLabel to table or to main.
>
> Qt version 4.5.0, PyQt4 version 4.4.4 (kubuntu 9.04)
> Qt version 4.4.3, PyQt4 version 4.4.3 (SuSE 11.1)
>
> Best regards
>
> Ole
>
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