[Solved] Running function with QtConcurrent::run

McLion

Hi

I have a function
char QTGUI_MainWindow::FormatSDcardForLivePause(void)
that I need to run in a separate thread and catch when it has finished without blocking the rest of the application.
I am trying as follows:

QFutureWatcher<char> watcher;
connect(&watcher, SIGNAL(finished()), this, SLOT(handleFinished()));
QFuture<char> future = QtConcurrent::run(FormatSDcardForLivePause);
watcher.setFuture(future);

According: http://doc.qt.io/qt-4.8/qtconcurrentrun.html
I get a
no matching function for call to 'run(<unresolved overload function type>)

What am I doing wrong?
Thanks
McL

SGaist

Hi,

You function belongs to QTGUI_MainWindow, see QtConcurrentRun using member functions

JKSH

@McLion said:

I get a
no matching function for call to 'run(<unresolved overload function type>)

See the documentation on how to use QtConcurrent::run() on class member functions: http://doc.qt.io/qt-5/qtconcurrentrun.html#using-member-functions

Please remember that functions for GUI-related classes cannot be called from another thread.

McLion

Thank you guys.
It is working now and the function perfectly runs in a different thread. Thanks also for the hint with the GUI-related classes. I had some output to the GUI that generated errors at runtime and did not show. Funny it did show once the GUI was hide and show again. So, if I need the output, I will have to implement something different.

However, I still have an issue with the FutureWatcher. The SLOT that should be called upon finished never gets called.

QFutureWatcher<char> watcher;
connect(&watcher, SIGNAL(finished()), this, SLOT(FinishedFormat()));
QFuture<char> Format = QtConcurrent::run(this, &QTGUI_MainWindow::FormatSDcardForLivePause);
watcher.setFuture(Format);

void QTGUI_MainWindow::FinishedFormat()

I need to know when it's finished as well as getting the return value (false or true - not implemented yet). Any idea what I am doing wrong that it gets not called at all?

McLion

Update:
Found the cause for the SLOT not being called. Moved declaration of QFutureWatcher and QFuture to the constructor of the class:

FormatWatcher = new QFutureWatcher<char>;
QFuture<char> Format;
connect(FormatWatcher, SIGNAL(finished()), this, SLOT(FinishedFormat()));

Now trying to get the result/return value ...

SGaist

FormatWatcher = new QFutureWatcher<char>;
QFuture<char> Format;
connect(FormatWatcher, SIGNAL(finished()), this, SLOT(FinishedFormat()));
watcher->setFuture(Format);

Then you can retrieve the future from the watcher and get the result you need

McLion

Everything works as supposed now.
Calling cSuccess = FormatWatcher->result(); in the FinishedFormat SLOT gets the result.

SGaist

I've missed that one :D Thanks for reminding me.

McLion

I'd like to add:

Specially if the Watcher needs to be used multiple times it's important to disconnect it after use:

disconnect(FormatWatcher, SIGNAL(finished()), this, SLOT(FinishedFormat()));       // disconnect former slot used with watcher