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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.

Constant Value Description
QNearFieldTarget::UnknownAccess 0x00 The target supports an unknown access type.
QNearFieldTarget::NdefAccess 0x01 The target supports reading and writing NDEF messages using readNdefMessages() and writeNdefMessages().
QNearFieldTarget::TagTypeSpecificAccess 0x02 The target supports sending tag type specific commands using sendCommand().
QNearFieldTarget::AnyAccess 0xff The 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.

Constant Value Description
QNearFieldTarget::NoError 0 No error has occurred.
QNearFieldTarget::UnknownError 1 An unidentified error occurred.
QNearFieldTarget::UnsupportedError 2 The requested operation is unsupported by this near field target.
QNearFieldTarget::TargetOutOfRangeError 3 The target is no longer within range.
QNearFieldTarget::NoResponseError 4 The target did not respond.
QNearFieldTarget::ChecksumMismatchError 5 The checksum has detected a corrupted response.
QNearFieldTarget::InvalidParametersError 6 Invalid parameters were passed to a tag type specific function.
QNearFieldTarget::ConnectionError 7 Failed to connect to the target.
QNearFieldTarget::NdefReadError 8 Failed to read NDEF messages from the target.
QNearFieldTarget::NdefWriteError 9 Failed to write NDEF messages to the target.
QNearFieldTarget::CommandError 10 Failed to send a command to the target.
QNearFieldTarget::TimeoutError 11 The 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.

Constant Value Description
QNearFieldTarget::ProprietaryTag 0 An unidentified proprietary target tag.
QNearFieldTarget::NfcTagType1 1 An NFC tag type 1 target.
QNearFieldTarget::NfcTagType2 2 An NFC tag type 2 target.
QNearFieldTarget::NfcTagType3 3 An NFC tag type 3 target.
QNearFieldTarget::NfcTagType4 4 An NFC tag type 4 target. This value is used if the NfcTagType4 cannot be further refined by NfcTagType4A or NfcTagType4B below.
QNearFieldTarget::NfcTagType4A 5 An NFC tag type 4 target based on ISO/IEC 14443-3A.
QNearFieldTarget::NfcTagType4B 6 An NFC tag type 4 target based on ISO/IEC 14443-3B.
QNearFieldTarget::MifareTag 7 A 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 support 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.

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.

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