Update QMessageBox continuously within specific function in Qt - qt

Question

I have a program which when it runs, at first the user is asked to initialize the system. In that question form, there are 3 checkboxes that the user can check them for specific person or every persons and the system initializes the items related to that checkbox for the person(s).
When a checkbox is selected, a specific function and subsequently the specific class is called and initialization is done.
In the mainwindow.cpp I have:
InitializeDialog *id=new InitializeDialog;
connect(id,&InitializeDialog::initializeSignal,this,&MainWindow::initializeSlot);
id->exec();
id is the question form which has 3 checkboxes in it. And:
void MainWindow::initializeSlot(QStringList persons, bool interests, bool plots, bool graphs)
{
initializeMBox->setWindowTitle(tr("Initializing System")+"...");
initializeMBox->setText(tr("Please wait until initialization has been done") + ".<br>");
initializeMBox->show();
initializeMBox->setStandardButtons(0);
if (interests)//checkbox 1 is checked
initializeInterests(persons);
if (plots)//checkbox 2 is checked
initializePlots(persons);
if(graphs)//checkbox 3 is checked
initializeGraphs(persons);
initializeMBox->setStandardButtons(QMessageBox::Ok);
}
And again:
void MainWindow::initializeInterests(QStringList persons)
{
for(int p=0;p<persons_comboBox_->count();p++)
{
persons_comboBox_->setCurrentIndex(p);
if (persons.contains(persons_comboBox_->currentText()))
{
//..
//create a specific class object and some specific functions
//..
//*
initializeMBox->setText(initializeMBox->text() + "<div><img src=\":/tickIcon.png\" height=\"10\" width=\"10\">" + " " + tr("Interests analyzed for the persons") + ": " + persons_comboBox_->currentText() + ".</div>");
}
}
}
initializePlots and initializeGraphs are similiar to initializeInterests.
The problem starts from here:
I want to show a message after initialization for every person (as I mentioned by star in initializeInterests) but my initializeMBox (is a QMessageBox) does not show the message continuously and when all persons are initialized, all messages are shown suddenly. It should be noted that I see my initializeMBox is getting bigger but it seems that my QMessageBox is Freezed.
I can't use QtConcurrent::run because my QMessageBox is updated from mainwindow (and so from the base thread) by the line that I mentioned by star.
How can I have a QMessageBox which be updated continuously?

Answer 1

Don't reenter the event loop. Replace id->exec() with id->show(). Manage the dialog's lifetime - perhaps it shouldn't be dynamically created at all.
Don't block in initializeInterests. Instead of changing the combo box, get its data, send it out to an async job, set everything up there, then send the results back.
Pass containers by const reference, not value.
Don't create strings by concatenation.
If the input persons list is long, sort it to speed up look-ups.
For example:
class StringSignal : public QObject {
Q_OBJECT
public:
Q_SIGNAL void signal(const QString &);
};
void MainWindow::initializeInterests(const QStringList &personsIn) {
auto in = personsIn;
std::sort(in.begin(), in.end());
QStringList persons;
persons.reserve(in.size());
for (int i = 0; i < persons_comboBox_->count(); ++i) {
auto const combo = persons_comboBox->itemText(i);
if (std::binary_search(in.begin(), in.end(), combo))
persons << combo;
}
QtConcurrent::run([persons = std::move(persons), w = this](){
StringSignal source;
connect(&source, &StringSignal::signal, w, [w](const QString & person){
w->initalizeMBox->setText(
QStringLiteral("%1 <div><img src=...> %2: %3.</div>")
.arg(w->initalizeMBox->text())
.arg(tr("Interests analyzed for the person"))
.arg(person)
);
});
for (auto &person : persons) { // persons is const
// create a specific object etc.
QThread::sleep(1); // let's pretend we work hard here
source.signal(person);
}
});
}
The creation of the "specific objects" you allude to should not access anything in the gui thread. If it doesn't - pass a copy of the required data, or access it in a thread-safe manner. Sometimes it makes sense, instead of copying the data, move it into the worker, and then when the worker is done - move it back into the gui, by the way of a lambda.