QNearFieldTarget Class

The QNearFieldTarget class provides an interface for communicating with a target device. More...

Header: #include <QNearFieldTarget>
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

class RequestId
enum AccessMethod { UnknownAccess, NdefAccess, TagTypeSpecificAccess, AnyAccess }
flags AccessMethods
enum Error { NoError, UnknownError, UnsupportedError, TargetOutOfRangeError, NoResponseError, …, TimeoutError }
enum Type { ProprietaryTag, NfcTagType1, NfcTagType2, NfcTagType3, NfcTagType4, …, MifareTag }

Public Functions

QNearFieldTarget(QObject *parent = nullptr)
virtual ~QNearFieldTarget()
QNearFieldTarget::AccessMethods accessMethods() const
bool disconnect()
bool hasNdefMessage()
int maxCommandLength() const
QNearFieldTarget::RequestId readNdefMessages()
QVariant requestResponse(const QNearFieldTarget::RequestId &id) const
QNearFieldTarget::RequestId sendCommand(const QByteArray &command)
QNearFieldTarget::Type type() const
QByteArray uid() const
bool waitForRequestCompleted(const QNearFieldTarget::RequestId &id, int msecs = 5000)
QNearFieldTarget::RequestId writeNdefMessages(const QList<QNdefMessage> &messages)


void disconnected()
void error(QNearFieldTarget::Error error, const QNearFieldTarget::RequestId &id)
void ndefMessageRead(const QNdefMessage &message)
void requestCompleted(const QNearFieldTarget::RequestId &id)

Detailed Description

QNearFieldTarget provides a generic interface for communicating with an NFC target device. Both NFC Forum devices and NFC Forum Tag targets are supported by this class. All target specific classes subclass this class.

The type() function can be used to get the type of the target device. The uid() function returns the unique identifier of the target. The AccessMethods flags returns from the accessMethods() function can be tested to determine which access methods are supported by the target.

If the target supports NdefAccess, hasNdefMessage() can be called to test if the target has a stored NDEF message, readNdefMessages() and writeNdefMessages() functions can be used to get and set the NDEF message.

If the target supports TagTypeSpecificAccess, sendCommand() can be used to send a single proprietary command to the target and retrieve the response.

Member Type Documentation

enum QNearFieldTarget::AccessMethod
flags QNearFieldTarget::AccessMethods

This enum describes the access methods a near field target supports.

QNearFieldTarget::UnknownAccess0x00The target supports an unknown access type.
QNearFieldTarget::NdefAccess0x01The target supports reading and writing NDEF messages using readNdefMessages() and writeNdefMessages().
QNearFieldTarget::TagTypeSpecificAccess0x02The target supports sending tag type specific commands using sendCommand().
QNearFieldTarget::AnyAccess0xffThe target supports any of the known access types.

The AccessMethods type is a typedef for QFlags<AccessMethod>. It stores an OR combination of AccessMethod values.

enum QNearFieldTarget::Error

This enum describes the error codes that a near field target reports.

QNearFieldTarget::NoError0No error has occurred.
QNearFieldTarget::UnknownError1An unidentified error occurred.
QNearFieldTarget::UnsupportedError2The requested operation is unsupported by this near field target.
QNearFieldTarget::TargetOutOfRangeError3The target is no longer within range.
QNearFieldTarget::NoResponseError4The target did not respond.
QNearFieldTarget::ChecksumMismatchError5The checksum has detected a corrupted response.
QNearFieldTarget::InvalidParametersError6Invalid parameters were passed to a tag type specific function.
QNearFieldTarget::ConnectionError7Failed to connect to the target.
QNearFieldTarget::NdefReadError8Failed to read NDEF messages from the target.
QNearFieldTarget::NdefWriteError9Failed to write NDEF messages to the target.
QNearFieldTarget::CommandError10Failed to send a command to the target.
QNearFieldTarget::TimeoutError11The request could not be completed within the time specified in waitForRequestCompleted().

enum QNearFieldTarget::Type

This enum describes the type of tag the target is detected as.

QNearFieldTarget::ProprietaryTag0An unidentified proprietary target tag.
QNearFieldTarget::NfcTagType11An NFC tag type 1 target.
QNearFieldTarget::NfcTagType22An NFC tag type 2 target.
QNearFieldTarget::NfcTagType33An NFC tag type 3 target.
QNearFieldTarget::NfcTagType44An NFC tag type 4 target. This value is used if the NfcTagType4 cannot be further refined by NfcTagType4A or NfcTagType4B below.
QNearFieldTarget::NfcTagType4A5An NFC tag type 4 target based on ISO/IEC 14443-3A.
QNearFieldTarget::NfcTagType4B6An NFC tag type 4 target based on ISO/IEC 14443-3B.
QNearFieldTarget::MifareTag7A Mifare target.

Member Function Documentation

QNearFieldTarget::QNearFieldTarget(QObject *parent = nullptr)

Constructs a new near field target with parent.

[signal] void QNearFieldTarget::disconnected()

This signal is emitted when the near field target moves out of proximity.

[signal] void QNearFieldTarget::error(QNearFieldTarget::Error error, const QNearFieldTarget::RequestId &id)

This signal is emitted when an error occurs while processing request id. The error parameter describes the error.

[signal] void QNearFieldTarget::ndefMessageRead(const QNdefMessage &message)

This signal is emitted when a complete NDEF message has been read from the target.

See also readNdefMessages().

[signal] void QNearFieldTarget::requestCompleted(const QNearFieldTarget::RequestId &id)

This signal is emitted when a request id completes.

See also sendCommand().

[virtual] QNearFieldTarget::~QNearFieldTarget()

Destroys the near field target.

QNearFieldTarget::AccessMethods QNearFieldTarget::accessMethods() const

Returns the access methods supported by this near field target.

[since 5.9] bool QNearFieldTarget::disconnect()

Closes the connection to the target to enable communication with the target from a different instance. The connection will also be closed, when the QNearFieldTarget is destroyed. A connection to the target device is (re)created to process a command or read/write a NDEF messages.

Returns true only if an existing connection was successfully closed; otherwise returns false.

This function was introduced in Qt 5.9.

bool QNearFieldTarget::hasNdefMessage()

Returns true if at least one NDEF message is stored on the near field target; otherwise returns false.

[since 5.9] int QNearFieldTarget::maxCommandLength() const

Returns the maximum number of bytes that can be sent with sendCommand. 0 will be returned if the target does not support sending tag type specific commands.

This function was introduced in Qt 5.9.

See also sendCommand().

QNearFieldTarget::RequestId QNearFieldTarget::readNdefMessages()

Starts reading NDEF messages stored on the near field target. Returns a request id which can be used to track the completion status of the request. An invalid request id will be returned if the target does not support reading NDEF messages.

An ndefMessageRead() signal will be emitted for each NDEF message. The requestCompleted() signal will be emitted was all NDEF messages have been read. The error() signal is emitted if an error occurs.

Note: An attempt to read an NDEF message from a tag, that is in INITIALIZED state as defined by NFC Forum, will fail with the NdefReadError, as the tag is formatted to support NDEF but does not contain a message yet.

QVariant QNearFieldTarget::requestResponse(const QNearFieldTarget::RequestId &id) const

Returns the decoded response for request id. If the request is unknown or has not yet been completed an invalid QVariant is returned.

QNearFieldTarget::RequestId QNearFieldTarget::sendCommand(const QByteArray &command)

Sends command to the near field target. Returns a request id which can be used to track the completion status of the request. An invalid request id will be returned if the target does not support sending tag type specific commands.

The requestCompleted() signal will be emitted on successful completion of the request; otherwise the error() signal will be emitted.

Once the request completes successfully the response can be retrieved from the requestResponse() function. The response of this request will be a QByteArray.

See also requestCompleted() and waitForRequestCompleted().

QNearFieldTarget::Type QNearFieldTarget::type() const

Returns the type of tag type of this near field target.

QByteArray QNearFieldTarget::uid() const

Returns the UID of the near field target.

Note: On iOS, this function returns an empty QByteArray for a near field target discovered using NdefAccess method.

See also QNearFieldTarget::AccessMethod.

bool QNearFieldTarget::waitForRequestCompleted(const QNearFieldTarget::RequestId &id, int msecs = 5000)

Waits up to msecs milliseconds for the request id to complete. Returns true if the request completes successfully and the requestCompeted() signal is emitted; otherwise returns false.

QNearFieldTarget::RequestId QNearFieldTarget::writeNdefMessages(const QList<QNdefMessage> &messages)

Writes the NDEF messages in messages to the target. Returns a request id which can be used to track the completion status of the request. An invalid request id will be returned if the target does not support reading NDEF messages.

The requestCompleted() signal will be emitted when the write operation completes successfully; otherwise the error() signal is emitted.

© 2022 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.