Publish and Subscribe Example

Publisher

When acting as a publisher of Value Space content the program creates a PublisherDialog. This dialog contains a widget for setting the base path of the QValueSpacePublisher and widgets for setting the value of the two fixed attributes 'intValue' and 'stringValue'.

We declare three slots which we will use to respond to user input in the dialog.

    private slots:
        void createNewObject();
        void intValueChanged(int value);
        void setStringValue();
        void setByteArrayValue();

And connect them to signals from the widgets in the constructor.

        connect(ui->connectButton, SIGNAL(clicked()), this, SLOT(createNewObject()));
        connect(ui->intValue, SIGNAL(valueChanged(int)), this, SLOT(intValueChanged(int)));
        connect(ui->setStringButton, SIGNAL(clicked()), this, SLOT(setStringValue()));
        connect(ui->setByteArrayButton, SIGNAL(clicked()), this, SLOT(setByteArrayValue()));

To publish values in the Value Space we first need to create a QValueSpacePublisher. We do this in the createNewObject() slot, which is also used to handle changes in the base path. After the object is constructed we publish the initial values by explicitly calling the other two slots.

    void PublisherDialog::createNewObject()
    {
        if (publisher)
            delete publisher;

        publisher = new QValueSpacePublisher(ui->basePath->text());
        intValueChanged(ui->intValue->value());
        setStringValue();
        setByteArrayValue();
    }

We use QValueSpacePublisher::setValue() to set the values in response to dialog input.

    void PublisherDialog::intValueChanged(int value)
    {
        publisher->setValue("intValue", value);
    }

    void PublisherDialog::setStringValue()
    {
        publisher->setValue("stringValue", ui->stringValue->text());
    }

    void PublisherDialog::setByteArrayValue()
    {
        publisher->setValue("byteArrayValue", ui->byteArrayValue->text().toAscii());
    }

As a final step in the constructor we explicitly call the createNewObject() slot to create an initial QValueSpacePublisher.

        createNewObject();

Subscriber

When acting as a subscriber of Value Space content the program creates a SubscriberDialog. This dialog contains a widget for setting the base path of the QValueSpaceSubscriber and a table for displaying all of the values directly under base path in the Value Space.

We declare two slots to propagate values from the Value Space to the dialog in response to change notifications from QValueSpaceSubscriber.

    private slots:
        void changeSubscriberPath();
        void subscriberChanged();

To read values from the Value Space we first create a QValueSpaceSubscriber and connect to the contentsChanged() signal.

We explicitly call our itemChanged() slot to populate the table with the initial values.

    void SubscriberDialog::changeSubscriberPath()
    {
        ui->values->clearContents();

        if (!subscriber)
            subscriber = new QValueSpaceSubscriber(ui->basePath->text(), this);
        else
            subscriber->setPath(ui->basePath->text());

        connect(subscriber, SIGNAL(contentsChanged()), this, SLOT(subscriberChanged()));

        subscriberChanged();
    }

In response to the contentsChanged() signal we update all the values in the table.

    void SubscriberDialog::subscriberChanged()
    {
        ui->values->clearContents();

        QStringList subPaths = subscriber->subPaths();
        ui->values->setRowCount(subPaths.count());

        for (int i = 0; i < subPaths.count(); ++i) {
            QVariant v = subscriber->value(subPaths.at(i));

            QTableWidgetItem *pathItem = new QTableWidgetItem(subPaths.at(i));
            QTableWidgetItem *valueItem = new QTableWidgetItem(v.toString());
            QTableWidgetItem *typeItem = new QTableWidgetItem(v.typeName());
            ui->values->setItem(i, 0, pathItem);
            ui->values->setItem(i, 1, valueItem);
            ui->values->setItem(i, 2, typeItem);
        }
    }