Dynamic QWidget for QStackedWidget using ID

[hobbyProgrammer]

I have an application with a mainwindow and a stackedwidget.
I like to create a widget that displays all the information about a formula 1 circuit, but it needs to be dynamic. I don't want to create a widget for each circuit, but I want it to retreive the data from the database using its ID.
I promoted the first index of the stacked widget to Circuit and already tried this:

Circuit.h:

    explicit Circuit(int ID,QWidget *parent = nullptr);

Circuit.cpp:

Circuit::Circuit(int ID, QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Circuit)
{
    ui->setupUi(this);
}

but it gives me this error:

no matching function for call to 'Circuit::Circuit()'
no matching constructor for initialization of 'Circuit'

        page = new Circuit();
        page->setObjectName(QString::fromUtf8("page"));
        stackedWidget->addWidget(page);

Is there anyone who knows what the proper way to do this is?

[mrjj]

@hobbyProgrammer said in Dynamic QWidget for QStackedWidget using ID:

page = new Circuit();

Hi
You have to give it the int in the ctor
page = new Circuit(666);
( ps. do you store it in the Circuit class, the code dont show that at all )

[hobbyProgrammer]

@mrjj Hi, I don't store it yet. I'd like to create a good setup before starting into the actual coding.

From the MainWindow how do I call this?

    QSqlQuery query(db);
    query.prepare("SELECT DISTINCT(name) FROM circuit WHERE circuit_id = :circuitID");
    query.bindValue(":circuitID", circuitID);
    query.exec();

    QSqlQueryModel *model = new QSqlQueryModel();
    model->setQuery(query);

    for(int i = 0; i < model->rowCount(); i++)
    {
        QString strCircuitName = model->data(model->index(i,0)).toString();
        const char* charCircuitName = strCircuitName.toStdString().c_str();
        QAction *circuitAct = new QAction(tr(charCircuitName));
        ui->menuCircuits->addAction(circuitAct);
        connect(circuitAct, &QAction::triggered, this, &MainWindow::goToCircuit);
    }

void MainWindow::goToCircuit()
{
    qDebug() << "circuitID: " << circuitID;
    Circuit *circuit = new Circuit(circuitID);
    ui->stackedWidget->setCurrentWidget(circuit);
}

When I start the app it goes straight to the page with index 0 (because of the code below, that was causing the error previously).
Whenever I press either Circuit 1 or Circuit 2, it doesn't seem to do anything. I suspect that my connect isn't the proper way to do this, but how should I do this?

page = new Circuit(0);
page->setObjectName(QString::fromUtf8("page"));
stackedWidget->addWidget(page);

[JonB]

@hobbyProgrammer
I'm sorry I don't have time to answer the signal/slot/connect part, you'll perhaps want to use a C++ lambda for that, there are various ways but you need your slot to gain access to which circuit ID the action is for, in some shape or form.

But I couldn't help noticing:

        QString strCircuitName = model->data(model->index(i,0)).toString();
        const char* charCircuitName = strCircuitName.toStdString().c_str();
        QAction *circuitAct = new QAction(tr(charCircuitName));

You don't want to do it this way. At minimum from docs use:

Similarly, you can pass a QString to a function that takes a const char * argument using the qPrintable() macro which returns the given QString as a const char *. This is equivalent to calling <QString>.toLocal8Bit().constData().

Separately

    Circuit *circuit = new Circuit(circuitID);
    ui->stackedWidget->setCurrentWidget(circuit);

https://doc.qt.io/qt-5/qstackedwidget.html#setCurrentWidget

Sets the current widget to be the specified widget. The new current widget must already be contained in this stacked widget.

You're going to need a https://doc.qt.io/qt-5/qstackedwidget.html#addWidget.

[hobbyProgrammer]

@JonB Hi,
thanks for your help.
I really need to know how to load these Circuits in the menu dynamically tho. Is there anyone else who might know how to help me?

I thought it could be done using QSignalMap, but I can't seem to find the solution anywhere

[hobbyProgrammer]

This post is deleted!

[hobbyProgrammer]

Allright, I got it working. It might not be the most beautiful solution so any feedback on how to improve the code is always welcome, but this is what I got so far:

void MainWindow::fillCircuitMenu()
{
    QSqlQuery query(db);
    query.prepare("SELECT DISTINCT(name), id FROM circuit WHERE circuit_id = :circuitID");
    query.bindValue(":circuitID", circuitID);
    query.exec();

    QSqlQueryModel *model = new QSqlQueryModel();
    model->setQuery(query);

    for(int i = 0; i < model->rowCount(); i++)
    {
        QString strCircuitName = model->data(model->index(i,0)).toString();
        const char* charCircuitName = strCircuitName.toStdString().c_str();

        QAction *circuitAct = new QAction(tr(charCircuitName));
        this->circuitID = model->data(model->index(i,1)).toInt();
        ui->menuCircuits->addAction(circuitAct);

        Circuit *circuit = new Circuit(circuitID);
        qvCircuitMenu.insert(i, circuit);

        QSignalMapper *signalMapper = new QSignalMapper(this);
        connect(circuitAct, SIGNAL(triggered()), signalMapper, SLOT(map()));
        signalMapper->setMapping(circuitAct, circuitID);
        connect(signalMapper, SIGNAL(mapped(int)), this, SLOT(goToCircuit(int)));
    }
}

void MainWindow::goToCircuit(int index)
{
    qDebug() << "goToCircuit: " << index;
    Circuit *circuit = new Circuit(index);
    ui->stackedWidget->addWidget(circuit);
    ui->stackedWidget->setCurrentWidget(circuit);
}

[JonB]

@hobbyProgrammer
I don't know what is going on here, but I note that for a given circuitID you do two new Circuit(circuitID)s, one in fillCircuitMenu() and another any time slot goToCircuit(int index) is invoked. I don't know if that is correct, no re-use of same Circuit instance?

Separately, I don't think there is any need to use deprecated QSignalMapper any longer. You can replace with new signal/slot syntax (you should get away from SIGNAL/SLOT() macros in all new code) plus a lambda. See e.g. https://doc.qt.io/qt-5/qsignalmapper.html#details for an example of this.