How to update QTableWidget immediately?

  • Hello,
    I have a task, startet by user using signal-slot functionality which takes about 5-20 seconds.
    This task is mainly a for-next-statement, which calculates some things and fills a QTableWidget with the result, that means about 200 Items.
    I want, that the single result items are immedialely displayed. I can do this by calling "myTableWidget->repaint()" .
    But that causes the whole window to repaint (even is the visible area is full) and that makes it very very slow (2..3 times slower), compared without using ->repaint().
    But without repaint the Widget is only repainted after the for-next Statement (after that 5..20 seconds)
    I tried already a timer and repaint all 200ms, but that is not much better.
    ->update() does not help. Without repaint() the widget is only refreshed after i return from my slot (and after the for-next-statement is finished)

    Is there a easy way, to update/repaint ONLY the new items (i only append them at the end) in the QTableWidget? (like Explorer search for files....that list is updated immediately when some new files are found)
    I do not want to create a new task...i do not need to replay to user action during filling the TableWidget (no scrolling necessary till i finished)...and i do not want to use QTableView....

    is there still a possibility?

  • @tomweb Hi, and welcome to the Qt forum! You could try calling void QCoreApplication::processEvents(QEventLoop::ProcessEventsFlags flags = QEventLoop::AllEvents) instead of repaint(). Maybe that's faster.

  • Lifetime Qt Champion

    Hi and welcome to devnet,

    What about creating a loop through signals and slots ? That way you can keep your UI responsive.

    For example :

    void MyClass::processData()
        if (_itemList.isEmpty()) {
        int next = _itemList.takeFirst();
        // process
        _tableWidget->setItem(row, col, new QTableWidgetItem(processingResult));
        QTimer::singleShot(this, 0, &processData)

    You can even make tweak it and make it interruptible if needed.

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