Calling setPlainText() for an object of a different thread leads to assertion failure

[bmesing]

Hello,

I have the following code that is located in the run() method of my class which is derived from QThread:

_pEventNotifyDlg->_pDateDisplay->setText("Test1");
_pEventNotifyDlg->_pMessageDisplay->setPlainText("Test2");

_pEventNotifyDlg->_pDateDisplay->setText("Test1");
_pEventNotifyDlg->_pMessageDisplay->setPlainText("Test2");

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While the first call works fine, the second causes a crash with the following error message:

QObject::startTimer: timers cannot be started from another thread
QObject::connect: Cannot queue arguments of type 'QRectF'
ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 81d1800. 
Receiver '' (of type 'QTextDocument') was created in thread 8061188", file kernel/qcoreapplication.cpp, line 293
Aborted

QObject::startTimer: timers cannot be started from another thread
QObject::connect: Cannot queue arguments of type 'QRectF'
ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 81d1800. 
Receiver '' (of type 'QTextDocument') was created in thread 8061188", file kernel/qcoreapplication.cpp, line 293
Aborted

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The _pEventNotifyDlg is an instance of a dialog class which belongs to the main thread. _pDateDisplay is a QLabel, and _pMessageDisplay is a QTextBrowser. I do not see that I am sending any events there, but I guess it is triggered by the setPlainText() method call.

Can anybody explain that behaviour to me? Am I misunderstanding something fundamental about threads?

Thanks Ben

QT Version 4.1.3