qt4 - QT + How to call slot from custom C++ code running in a different thread

Question

I am new to QT and I am doing some learning.

I would like to trigger a slot that modify a GUI widget from a C++ thread(Currently a Qthread).

Unfortunatly I get a: ASSERTION failed at: Q_ASSERT(qApp && qApp->thread() == QThread::currentThread());

here is some code:

(MAIN + Thread class)

   class mythread : public QThread
    {
    public:
        mythread(mywindow* win){this->w = win;};
        mywindow* w;
        void run()
        {
            w->ui.textEdit->append("Hello");        //<--ASSERT FAIL
            //I have also try to call a slots within mywindow which also fail.
        };
    };

    int main(int argc, char *argv[])
    {
        QApplication* a = new QApplication(argc, argv);
        mywindow* w = new mywindow();

        w->show();
        mythread* thr = new mythread(w);
        thr->start();

        return a->exec();
    }

Window:

class mywindow : public QMainWindow
{
    Q_OBJECT

public:
    mywindow (QWidget *parent = 0, Qt::WFlags flags = 0);
    ~mywindow ();
    Ui::mywindow ui;

private:



public slots:
    void newLog(QString &log);
};

So I am curious on how to update the gui part by code in a different thread.

Thanks for helping

Answer 1

stribika got it almost right:

QMetaObject::invokeMethod( textEdit, "append", Qt::QueuedConnection,
                           Q_ARG( QString, myString ) );

cjhuitt's right, though: You usually want to declare a signal on the thread and connect it to the append() slot, to get object lifetime management for free (well, for the price of a minor interface change). On a sidenote, the additional argument:

               Qt::QueuedConnection ); // <-- This option is important!

from cjhuitt's answer isn't necessary anymore (it was, in Qt <= 4.1), since connect() defaults to Qt::AutoConnection which now (Qt >= 4.2) does the right thing and switches between queued and direct connection mode based on QThread::currentThread() and the thread affinity of the receiver QObject at emit time (instead of sender and receiver affinity at connect time).