QSerialPort stops responding while QFileDialog::getExistingDirectory is active - c++

Question

My application stops receiving data with QSerialPort while using QFileDialog::getExistingDirectory. It resumes receiving data after the closure of the dialog. Is there a way to prevent that?

Answer 1

You're calling a blocking method. While that method executes, the event loop can't run, because it's somewhere at the bottom of the call stack, waiting for your slot to return back to it. This is the synchronous way of coding that doesn't reflect what's really happening, as the world is asynchronous. So don't code that way.
Instead, you should set up the file dialog while it's invisible, then show() it, and have the desired code execute in a slot connected to the QDialog::accepted() signal.
You could factor the setup out and have a nice asynchronous helper, used similarly to getExistingDirectory:
template <typename F> void withExistingDirectoryDo(F && fun, QObject * context = 0,
QWidget * parent = 0, const QString & caption = QString(),
const QString & dir = QString(), Options options = QFileDialog::ShowDirsOnly) {
auto * dialog = new QFileDialog(parent);
auto helper = [fun, dialog]{ fun(dialog->directory()); };
if (context)
connect(dialog, &QDialog::accepted, context, helper);
else
connect(dialog, &QDialog::accepted, helper);
dialog->setAttribute(Qt::WA_DeleteOnClose);
dialog->setOptions(options);
dialog->setFileMode(QFileDialog::Directory);
dialog->show();
}
Here's the code transformation:
void before() {
foo();
auto dir = QFileDialog::getExistingDirectory(); // bad synchronous code
bar(dir);
}
void after() {
foo();
withExistingDirectoryDo([this](const QDir & dir) {
bar(dir);
}, this);
}