- Qt 6.5
- Qt NFC
- C++ Classes
- QNearFieldTarget
- Qt 6.5.0 Reference Documentation

# 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
Inherits: | QObject

- List of all members, including inherited members

## 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)

## Signals

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

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

Constructs a new near field target with parent.

### `[virtual]` QNearFieldTarget::~QNearFieldTarget()

Destroys the near field target.

### QNearFieldTarget::AccessMethods QNearFieldTarget::accessMethods() const

Returns the access methods supported by this near field target.

### 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`.

### `[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.

### bool QNearFieldTarget::hasNdefMessage()

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

### 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.

See also sendCommand().

### `[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().

### 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.

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

This signal is emitted when a request id completes.

See also sendCommand().

### 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.