QNearFieldManager Class

The QNearFieldManager class provides access to notifications for NFC events. More...

Header: #include <QNearFieldManager>
CMake: find_package(Qt6 REQUIRED COMPONENTS Nfc)
target_link_libraries(mytarget PRIVATE Qt6::Nfc)
qmake: QT += nfc
Since: Qt 5.2
Inherits: QObject

Public Types

enum class AdapterState { Offline, TurningOn, Online, TurningOff }

Public Functions

QNearFieldManager(QObject *parent = nullptr)
virtual ~QNearFieldManager()
bool isEnabled() const
bool isSupported(QNearFieldTarget::AccessMethod accessMethod = QNearFieldTarget::AnyAccess) const
void setUserInformation(const QString &message)
bool startTargetDetection(QNearFieldTarget::AccessMethod accessMethod)
void stopTargetDetection(const QString &errorMessage = QString())


void adapterStateChanged(QNearFieldManager::AdapterState state)
void targetDetected(QNearFieldTarget *target)
void targetDetectionStopped()
void targetLost(QNearFieldTarget *target)

Detailed Description

NFC Forum devices support two modes of communications. The first mode, peer-to-peer communications, is used to communicate between two NFC Forum devices. The second mode, master/slave communications, is used to communicate between an NFC Forum device and an NFC Forum Tag or Contactless Card. The targetDetected() signal is emitted when a target device enters communications range. Communications can be initiated from the slot connected to this signal.

NFC Forum devices generally operate as the master in master/slave communications. Some devices are also capable of operating as the slave, so called Card Emulation mode. In this mode the local NFC device emulates a NFC Forum Tag or Contactless Card.

Applications can connect to the targetDetected() and targetLost() signals to get notified when an NFC Forum Tag enters or leaves proximity. Before these signals are emitted target detection must be started with the startTargetDetection() function. Target detection can be stopped with the stopTargetDetection() function. When the target is no longer required the target should be deleted as other applications may be blocked from accessing the target.

Member Type Documentation

[since 5.12] enum class QNearFieldManager::AdapterState

This enum describes the different states a NFC adapter can have.

QNearFieldManager::AdapterState::Offline1The nfc adapter is offline.
QNearFieldManager::AdapterState::TurningOn2The nfc adapter is turning on.
QNearFieldManager::AdapterState::Online3The nfc adapter is online.
QNearFieldManager::AdapterState::TurningOff4The nfc adapter is turning off.

This enum was introduced or modified in Qt 5.12.

Member Function Documentation

QNearFieldManager::QNearFieldManager(QObject *parent = nullptr)

Constructs a new near field manager with parent.

[signal, since 5.12] void QNearFieldManager::adapterStateChanged(QNearFieldManager::AdapterState state)

This signal is emitted whenever the state of the NFC adapter changed.

Note: Currently, this signal is only emitted on Android.

This function was introduced in Qt 5.12.

[signal] void QNearFieldManager::targetDetected(QNearFieldTarget *target)

This signal is emitted whenever a target is detected. The target parameter represents the detected target.

This signal will be emitted for all detected targets.

QNearFieldManager maintains ownership of target, however, it will not be destroyed until the QNearFieldManager destructor is called. Ownership may be transferred by calling setParent().

Do not delete target from the slot connected to this signal, instead call deleteLater().

Note: that if target is deleted before it moves out of proximity the targetLost() signal will not be emitted.

See also targetLost().

[signal, since 6.2] void QNearFieldManager::targetDetectionStopped()

This signal is emitted whenever the target detection is stopped.

Note: Mostly this signal is emitted when stopTargetDetection() has been called. Additionally the user is able to stop the detection on iOS within a popup shown by the system during the scan, which also leads to emitting this signal.

This function was introduced in Qt 6.2.

[signal] void QNearFieldManager::targetLost(QNearFieldTarget *target)

This signal is emitted whenever a target moves out of proximity. The target parameter represents the lost target.

Do not delete target from the slot connected to this signal, instead use deleteLater().

See also QNearFieldTarget::disconnected().

[virtual] QNearFieldManager::~QNearFieldManager()

Destroys the near field manager.

[since 6.2] bool QNearFieldManager::isEnabled() const

Returns true if the device has a NFC adapter and it is turned on; otherwise returns false.

This function was introduced in Qt 6.2.

See also isSupported().

[since 5.12] bool QNearFieldManager::isSupported(QNearFieldTarget::AccessMethod accessMethod = QNearFieldTarget::AnyAccess) const

Returns true if the underlying device has a NFC adapter; otherwise returns false. If an accessMethod is given, the function returns true only if the NFC adapter supports the given accessMethod.

This function was introduced in Qt 5.12.

See also isEnabled().

[since 6.2] void QNearFieldManager::setUserInformation(const QString &message)

Sets the message shown to the user by the system. If the target detection is running the message will be updated immediately and can be used as a progress message. The last message set before a call to startTargetDetection() without an error message is used as a success message. If the target detection is not running the message will be used as the initial message when the next detection is started. By default no message is shown to the user.

Note: Currently, this function only has an effect on iOS because a popup is shown by the system during the scan. On iOS, this message is mapped to the alert message which is shown upon successful completion of the scan. Other platforms will ignore message.

This function was introduced in Qt 6.2.

See also startTargetDetection() and stopTargetDetection().

bool QNearFieldManager::startTargetDetection(QNearFieldTarget::AccessMethod accessMethod)

Starts detecting targets and returns true if target detection is successfully started; otherwise returns false. Causes the targetDetected() signal to be emitted when a target is within proximity. Only tags with the given accessMethod will be delivered. Active detection continues until stopTargetDetection() has been called.

To detect targets with a different accessMethod, stopTargetDetection() must be called first.

Note: On iOS it is impossible to start target detection for both NdefAccess and TagTypeSpecificAccess at the same time. So if AnyAccess is selected, NdefAccess will be used instead.

See also stopTargetDetection().

void QNearFieldManager::stopTargetDetection(const QString &errorMessage = QString())

Stops detecting targets. The targetDetected() signal will no longer be emitted until another call to startTargetDetection() is made. Targets detected before are still valid.

Note: On iOS, detected targets become invalid after this call (e.g. an attempt to write or read NDEF messages will result in an error).

If an errorMessage is provided, this is a hint to the system that the goal, the application had, was not reached. The errorMessage and a matching error icon are shown to the user. Calling this function with an empty errorMessage, implies a successful operation end; otherwise an errorMessage should be passed to this function.

Note: Currently, errorMessage only has an effect on iOS because a popup is shown by the system during the scan where the errorMessage is visible. Other platforms will ignore this parameter.

See also setUserInformation().

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