How can I run my Qt function after a thread has finished? - c++

Question

void MainWindow::on_pushButton_clicked()
{
QFuture<int> future = QtConcurrent::run(identify); //Thread1
if (future.isFinished())
{
//DoSomething();
}
}
I have this code. I want to run the DoSomething() function after the identify function finished running. Is it possible?

Answer 1

You can pass the QFuture object to a QFutureWatcher and connect its finished() signal to the function or slot DoSomething().
For example:
void MainWindow::on_pushButton_clicked()
{
QFuture<int> future = QtConcurrent::run(identify); //Thread1
QFutureWatcher<int> *watcher = new QFutureWatcher<int>(this);
connect(watcher, SIGNAL(finished()), this, SLOT(doSomething()));
// delete the watcher when finished too
connect(watcher, SIGNAL(finished()), watcher, SLOT(deleteLater()));
watcher->setFuture(future);
}
void MainWindow::DoSomething() // slot or ordinary function
{
// ...
}
Or you could use a nested event loop to keep the GUI responsive and have everything inside the same function:
void MainWindow::on_pushButton_clicked()
{
QFuture<int> future = QtConcurrent::run(identify); //Thread1
QFutureWatcher<int> watcher;
QEventLoop loop;
// QueuedConnection is necessary in case the signal finished is emitted before the loop starts (if the task is already finished when setFuture is called)
connect(&watcher, SIGNAL(finished()), &loop, SLOT(quit()), Qt::QueuedConnection);
watcher.setFuture(future);
loop.exec();
DoSomething();
}

Answer 2

I like this call layout.
auto watcher = new QFutureWatcher<int>(this);
connect(watcher, &QFutureWatcher<int>::finished,
[watcher, this] ()
{
watcher->deleteLater();
auto res = watcher->result();
// ...
});
watcher->setFuture(QtConcurrent::run(identify, param1, param2));