QThread and GUI

[jesse_mark]

Hello,

I am trying to use QThread with GUI application, so the GUI wont stall on me.

in th GUI, i have a window through witch i load a Txt file and parse it and do processing on it, they are in this manner

loadFile (... )
{
  readFile(..);
  parseFile(..);
  prossValues(...);
}

loadFile (... )
{
  readFile(..);
  parseFile(..);
  prossValues(...);
}

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when i run the loadFile slot, it takes long time, and the GUI stalls.

what i did so far, is

I sub-classed the QThread,
override the run method and,
emit a signal called loadFile(). in the run method.


In the class where i need to load the file ,
I create a mythread and,
connect the loadFile signal to a loadFile slot.

the the signal triggers fine and i load the file, but the gui still stalls,
which i think it means that im still running on the main thread. not on the thread i created.

so, Please let me know what im missing and what the mistake im making and how can i fix it.

Thanks

Jesse.

[wysota]

We'd need to see the actual code. Bear in mind that QThread object lives in the main thread and not in the thread it represents, that's probably your issue.

Anyway, I suggest you use QtConcurrent::run() instead of a standalone QThread. For such simple usecases it's much easier to use.

QString loadTextFile(const QString &fileName) {
  QFile f(fileName);
  if(!f.open(...)) return QString();
  QTextStream stream(&f);
  return stream.readAll();
}
 
// ...
QFutureWatcher<QString> *futureWatcher = new ...; // optional
connect(futureWatcher, SIGNAL(finished()), this, SLOT(...))); // optional
QFuture<QString> future = QtConcurrent::run(loadTextFile, QStringLiteral("somefile.txt"));
futureWatcher->setFuture(future); // optional
 
// ... do something in the meantime
 
QString content = future.result(); // will block if the result is not ready (alternative to useing QFutureWatcher)

QString loadTextFile(const QString &fileName) {
  QFile f(fileName);
  if(!f.open(...)) return QString();
  QTextStream stream(&f);
  return stream.readAll();
}

// ...
QFutureWatcher<QString> *futureWatcher = new ...; // optional
connect(futureWatcher, SIGNAL(finished()), this, SLOT(...))); // optional
QFuture<QString> future = QtConcurrent::run(loadTextFile, QStringLiteral("somefile.txt"));
futureWatcher->setFuture(future); // optional

// ... do something in the meantime

QString content = future.result(); // will block if the result is not ready (alternative to useing QFutureWatcher)

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