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c++multithreadingqtqtconcurrent

Connecting signals/slots on separate thread using QtConcurrent::run

In my application I have the following code in a dialog:

connect(drive, SIGNAL(FileProgressChanged(Progress)), SLOT(OnFileProgressChanged(Progress)));

QtConcurrent::run(this, &ProgressDialog::PerformOperation, Operation, *Path, OutPath, drive);

The PerformOperation function eventually calls to a function in drive which emits the signal FileProgressChanged, and my OnFileProgressChanged function is as follows:

void ProgressDialog::OnFileProgressChanged(Progress p)
{
    if (ui->progressCurrent->maximum() != p.Maximium)
        ui->progressCurrent->setMaximum(p.Maximium);

    ui->progressCurrent->setValue(p.Current);

    if (ui->groupBoxCurrent->title().toStdString() != p.FilePath)
        ui->groupBoxCurrent->setTitle(QString::fromStdString(p.FilePath));
}

I was doing some reading and saw that QFuture and QFutureWatcher support monitoring progress values (which would work great in this situation!), but those cannot be used in conjunction with QtConcurrent::run.

How would I go about connecting the signal that gets moved emitted on the separate thread to the slot on my main thread so I can monitor the progress of the function called on the emitter thread?

*Edit -- * I actually found an error with my code, but it doesn't seem to have an affect. I forgot to add this as an argument after the signal

connect(drive, SIGNAL(FileProgressChanged(Progress)), this, SLOT(OnFileProgressChanged(Progress)));
Solution

  • Try using connect() with QueuedConnection, like:

    connect(drive, SIGNAL(FileProgressChanged(Progress)), this, SLOT(OnFileProgressChanged(Progress)), Qt::QueuedConnection);

    The connection should already be queued by default (since the emitter and receiver are in different threads), but this just makes it more explicit.

    EDIT: The problem was that the Progress type wasn't registered with Qt's meta-object system. Adding qRegisterMetaType<Progress>("Progress"); fixed the problem.