CODEWITHSUNDEEP
c++qt
manatttta
manatttta

Reputation: 3124

Qt Busy Processing dialog

I have an App that consumes lots of time running an algorithm. When the filter is running, the GUI obviously blocks until the algorithm is finished.

For that reason I want to show a modal dialog while the algorithm runs, displaying a "Busy" message. This way, the GUI would still be responsive. I tried doing it as follows:

dialog->setModal(true);
dialog->show();

// Run the code that takes up a lot of time
....

dialog->close();

However, this way the dialog shows up but it's all black (it's not drawn), Hoe can I solve this?

Upvotes: 1

Views: 639

Answers (1)

k.v.
k.v.

Reputation: 1223

If GUI has to be responsive, heavy algorithm should run in non-main (non-GUI) thread. To be responsive, GUI has to have access to main thread to process events in event loop.

You can use QFuture with QtConcurrent::run to implement this.

Example of QFuture usage:

TAlgoResult HeavyAlgorithm() {/* Here is algorithm routine */};
QFuture<TAlgoResult> RunHeavyAlgorithmAsync() 
{
    QtConcurrent::run([&](){return HeavyAlgorithm();});
}

// class which calls algo
class AlgoCaller
{
    QFutureWatcher<TAlgoResult> m_future_watcher;
    QDialog*                    mp_modal_dialog;

    AlgoCaller()
    {
        QObject::connect(&m_future_watcher, &QFutureWatcher<void>::finished, 
        [&]()
        {
            mp_modal_dialog->close(); // close dialog when calculation finished
        })
    }

    void CallAlgo() // to be called from main thread
    {
        mp_modal_dialog->show(); // show dialog before algo start
        m_future_watcher.setFuture(RunHeavyAlgorithmAsync()); 
            // start algo in background

        // main thread is not blocked and events can be processed
    }

};

Upvotes: 3

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