This demo presents how to use NFC for communication using Qt framework on mobile platform. Application has simple UI and logic that can be an example of creative NFC usage. Demo presents following features:

• NFC tags detection
• NFC tags reading
• NFC tags writing
• Exposing C++ to Qml to build creative cooking mobile app 🍗 🍳

If you need more detailed blog post on NFC topic you can read this blog post on Scythe Studio blog. Here we will talk only about NFC tags detection.

We created a NFCManager class that among other members and methods, have important QNearFieldManager instance saved. Connecting to this object is crucial to control detection and handle signals.

// directives, forward declarations, structure declaration

class NFCManager : public QObject
{
    Q_OBJECT
    // properties
    QML_ELEMENT

public:
    explicit NFCManager(QObject *parent = nullptr);

    // ...

public slots:
    void startReading();
    void stopDetecting();
    void saveRecord(const QString &dishName, int seconds);

signals:
    // ...
    void recordChanged(const Record &record);
    void wroteSuccessfully();
    void nfcError(const QString &error);

private slots:
    // ...
    void onTargetDetected(QNearFieldTarget *target);
    void onTargetLost(QNearFieldTarget *target);

    void onNdefMessageRead(const QNdefMessage &message);
    void onNdefMessageWritten();
    void handleTargetError(QNearFieldTarget::Error error, const QNearFieldTarget::RequestId &id);

private:
    // ...
    QNearFieldManager *m_manager;
    QNearFieldTarget::RequestId m_request;
};

#endif // NFCMANAGER_H

Then we connect to register slots for two important signals emitted by QNearFieldManager instance. The first one - targetDetected, is emitted when target device (device, tag, card) goes into a range. When target device leaves communication range, targetLost signal is emitted.

NFCManager::NFCManager(QObject *parent)
    : QObject(parent)
    , m_manager(new QNearFieldManager(this))
{

    connect(m_manager, &QNearFieldManager::targetDetected,
            this, &NFCManager::onTargetDetected);
    connect(m_manager, &QNearFieldManager::targetLost,
            this, &NFCManager::onTargetLost);
}

And that's pretty it. This way you can detect tags, but before you will see slots executed, you need to ask QNearFieldManager to start detection. You start detection by calling startTargetDetection() method on manager, but first set target access mode by calling setTargetAccessModes(mode).

void NFCManager::startReading()
{
    // ...
    m_manager->setTargetAccessModes(QNearFieldManager::NdefReadTargetAccess);
    m_manager->startTargetDetection();
}

void NFCManager::stopDetecting()
{
    // ...
    m_manager->setTargetAccessModes(QNearFieldManager::NoTargetAccess);
    m_manager->stopTargetDetection();
}

Once you are done with your NFC feature you can call stopTargetDetection() to prevent future NFC target events.

Yeah so that's it. This Readme is already too long, so feel free to visit our blog to discover how to actually read and write messages from/on NFC tags.

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