CODEWITHSUNDEEP
c++qt
Martin
Martin

Reputation: 4862

How to show a QMessageBox completely before the next function call

I want to use a QMessageBox to announce a short waiting interval to the user.

QMessageBox* box(new QMessageBox(QMessageBox::Information,"Parser","Processing " + mFileName));
box->setStandardButtons(QMessageBox::NoButton);
box->setWindowModality(Qt::WindowModal);
box->show();
QApplication::processEvents();

parser.analyseFile(mFileName);

box->hide();
box->deleteLater();
QApplication::processEvents();

The function only takes few seconds. The box gets displayed but neither the icon nor the text is shown in time before the function finishes. Why does QApplication::processEvents(); not prevent the program from continuation before the box is completely shown. Is it possible to achieve the desired behaviour without resorting to threads.

Upvotes: 1

Views: 1059

Answers (1)

Jeremy Friesner
Jeremy Friesner

Reputation: 73294

Doing the processing in a separate thread would be preferable, since that would leave the GUI thread free to do things like handle mouse events, window resizes, etc, while the task is being completed; that way the GUI won't "freeze up" temporarily.

If you don't want to spawn a thread, however, you can call processEvents() periodically from within your analyseFile() function and that will give you roughly the same behavior. Try to call it at least every 50mS to avoid sluggish GUI response.

A second possibility might be to add a slot somewhere:

void MyClass :: ParseFile()
{
   parser.analyseFile(mFileName);
   box->hide();
   box->deleteLater();
}

... and then invoke that asynchronously like this:

QTimer::singleShot(0, this, SLOT(ParseFile()));

... that might give the windowing system enough time to finish displaying the QMessageBox before ParseFile() executes, or it might not (in which case you could try to increase the delay argument from 0 to, say, 100 milliseconds instead). That's a little hacky, but it could work.

Upvotes: 1

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