- Qt 6.8
- Qt NFC
- C++ Classes
- QNearFieldManager
- Qt 6.8.3 Reference Documentation

# 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`
Inherits: | QObject

- List of all members, including inherited members

## Public Types

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

## Public Functions

| QNearFieldManager(QObject *parent = nullptr)
virtual | ~QNearFieldManager()
`(since 6.2)` bool | isEnabled() const
bool | isSupported(QNearFieldTarget::AccessMethod accessMethod = QNearFieldTarget::AnyAccess) const
`(since 6.2)` void | setUserInformation(const QString &message)
bool | startTargetDetection(QNearFieldTarget::AccessMethod accessMethod)
void | stopTargetDetection(const QString &errorMessage = QString())

## Signals

void | adapterStateChanged(QNearFieldManager::AdapterState state)
void | targetDetected(QNearFieldTarget *target)
`(since 6.2)` 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.

##### NFC on Linux

The Linux NFC project provides software to support NFC on Linux platforms. The neard daemon will allow access to the supported hardware via DBus interfaces. QtNfc requires neard version 0.14 which can be built from source or installed via the appropriate Linux package manager. Not all API features are currently supported. To allow QtNfc to access the DBus interfaces the neard daemon has to be running. In case of problems debug output can be enabled by enabling categorized logging for 'qt.nfc.neard'.

## Member Type Documentation

### enum class QNearFieldManager::AdapterState

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

Constant | Value | Description
--- | --- | ---
`QNearFieldManager::AdapterState::Offline` | `1` | The nfc adapter is offline.
`QNearFieldManager::AdapterState::TurningOn` | `2` | The nfc adapter is turning on.
`QNearFieldManager::AdapterState::Online` | `3` | The nfc adapter is online.
`QNearFieldManager::AdapterState::TurningOff` | `4` | The nfc adapter is turning off.

## Member Function Documentation

### `[explicit]` QNearFieldManager::QNearFieldManager(QObject *parent = nullptr)

Constructs a new near field manager with parent.

### `[virtual noexcept]` QNearFieldManager::~QNearFieldManager()

Destroys the near field manager.

### `[signal]` 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.

### `[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().

### 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.

See also isEnabled().

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

Sets the message that the system shows to the user. If 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 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 the system shows a popup 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 started successfully; otherwise returns `false`. Causes the targetDetected() signal to be emitted when a target is within proximity. Only tags with the given accessMethod will be reported. Target detection continues until stopTargetDetection() is 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.

Note: On platforms using neard, target detection will stop as soon as a tag has been detected.

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

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

See also setUserInformation().

### `[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().