Class Tag

java.lang.Object
com.codename1.nfc.Tag
public abstract class Tag extends Object

A tag discovered by Nfc.readTag(NfcReadOptions) or Nfc.addTagListener(NfcListener). The lifetime of a Tag is tied to the reader session that produced it: once the tag leaves the field (or the caller closes the session) all subsequent calls on this instance fail with NfcError.TAG_LOST.

Apps inspect the tag via getTypes() to learn which technologies are available and call one of:

A Tag may return null from a technology accessor when the underlying tag does not support that technology (consult supports(TagType) first). Ports subclass Tag to provide the native transceive implementation -- application code never instantiates Tag directly.

  • Constructor Details

    • Tag

      protected Tag(Set<TagType> types, byte[] id)
      Subclasses populate the technology list and (when known) the tag's hardware UID. Pass an empty array for id if the platform does not expose one.

  • Method Details

    • getTypes

      public final Set<TagType> getTypes()
      Technologies advertised by this tag. Always at least one entry on a discovered tag; an empty set indicates a tag the platform could not classify (rare).

    • supports

      public final boolean supports(TagType t)
      Convenience: getTypes().contains(t).

    • getId

      public final byte[] getId()
      Tag's hardware identifier (NFCA.uid on iOS / Tag.getId() on Android). Defensively copied. Returns an empty array if the platform did not surface a UID.

    • readNdef

      public AsyncResource<NdefMessage> readNdef()
      Reads the NDEF message currently stored on this tag. Fails with NfcError.UNSUPPORTED_TAG if supports(TagType) of TagType.NDEF is false.

    • writeNdef

      public AsyncResource<Boolean> writeNdef(NdefMessage message)
      Writes (or overwrites) the NDEF message on this tag. Fails with NfcError.READ_ONLY if the tag has been locked, and with NfcError.CAPACITY_EXCEEDED when the serialised message is larger than getMaxNdefSize(). Default implementation reports NfcError.UNSUPPORTED_TAG.

    • makeReadOnly

      public AsyncResource<Boolean> makeReadOnly()
      Permanently locks the tag's NDEF area against future writes. Not all tags expose this operation -- on those the call fails with NfcError.UNSUPPORTED_TAG. Irreversible -- a locked tag cannot be re-armed.

    • getMaxNdefSize

      public int getMaxNdefSize()
      Largest NDEF message size (in bytes) that fits on this tag. Returns -1 when the platform does not expose the figure (iOS Core NFC hides it on non-NDEF-formatted tags).

    • isWritable

      public boolean isWritable()
      true when the tag's NDEF area is writable. Defaults to false on the base class.

    • hasNdef

      public boolean hasNdef()
      Convenience: true when readNdef() returns at least one NdefRecord right now. Defaults to supports(TagType.NDEF).

    • getIsoDep

      public IsoDep getIsoDep()
      Returns an IsoDep view of this tag for ISO 7816 / EMV / passport APDU exchange, or null if the tag does not advertise TagType.ISO_DEP.

    • getMifareClassic

      public MifareClassic getMifareClassic()
      Returns a MifareClassic view of this tag, or null when not supported. iOS always returns null for MIFARE Classic.

    • getMifareUltralight

      public MifareUltralight getMifareUltralight()
      Returns a MifareUltralight view, or null when not supported.

    • getNfcA

      public NfcA getNfcA()
      Raw NFC-A (ISO 14443-3A) transceive view, or null.

    • getNfcB

      public NfcB getNfcB()
      Raw NFC-B (ISO 14443-3B) transceive view, or null. Android-only.

    • getNfcF

      public NfcF getNfcF()
      Raw FeliCa (JIS X 6319-4) transceive view, or null.

    • getNfcV

      public NfcV getNfcV()
      Raw ISO 15693 / vicinity transceive view, or null. Android-only.