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Android Reference

Ndef


android.nfc.tech

Class Ndef

  • All Implemented Interfaces:
    TagTechnology, Closeable, AutoCloseable


    public final class Ndef
    extends Object
    Provides access to NDEF content and operations on a Tag.

    Acquire a Ndef object using get(android.nfc.Tag).

    NDEF is an NFC Forum data format. The data formats are implemented in NdefMessage and NdefRecord. This class provides methods to retrieve and modify the NdefMessage on a tag.

    There are currently four NFC Forum standardized tag types that can be formatted to contain NDEF data.

    It is mandatory for all Android devices with NFC to correctly enumerate Ndef on NFC Forum Tag Types 1-4, and implement all NDEF operations as defined in this class.

    Some vendors have there own well defined specifications for storing NDEF data on tags that do not fall into the above categories. Android devices with NFC should enumerate and implement Ndef under these vendor specifications where possible, but it is not mandatory. getType() returns a String describing this specification, for example MIFARE_CLASSIC is com.nxp.ndef.mifareclassic.

    Android devices that support MIFARE Classic must also correctly implement Ndef on MIFARE Classic tags formatted to NDEF.

    For guaranteed compatibility across all Android devices with NFC, it is recommended to use NFC Forum Types 1-4 in new deployments of NFC tags with NDEF payload. Vendor NDEF formats will not work on all Android devices.

    Note: Methods that perform I/O operations require the android.Manifest.permission#NFC permission.

    • Method Detail

      • get

        public static Ndef get(Tag tag)
        Get an instance of Ndef for the given tag.

        Returns null if Ndef was not enumerated in Tag.getTechList(). This indicates the tag is not NDEF formatted, or that this tag is NDEF formatted but under a vendor specification that this Android device does not implement.

        Does not cause any RF activity and does not block.

        Parameters:
        tag - an NDEF compatible tag
        Returns:
        Ndef object
      • getCachedNdefMessage

        public NdefMessage getCachedNdefMessage()
        Get the NdefMessage that was read from the tag at discovery time.

        If the NDEF Message is modified by an I/O operation then it will not be updated here, this function only returns what was discovered when the tag entered the field.

        Note that this method may return null if the tag was in the INITIALIZED state as defined by NFC Forum, as in this state the tag is formatted to support NDEF but does not contain a message yet.

        Does not cause any RF activity and does not block.

        Returns:
        NDEF Message read from the tag at discovery time, can be null
      • getMaxSize

        public int getMaxSize()
        Get the maximum NDEF message size in bytes.

        Does not cause any RF activity and does not block.

        Returns:
        size in bytes
      • isWritable

        public boolean isWritable()
        Determine if the tag is writable.

        NFC Forum tags can be in read-only or read-write states.

        Does not cause any RF activity and does not block.

        Requires android.Manifest.permission#NFC permission.

        Returns:
        true if the tag is writable
      • getNdefMessage

        public NdefMessage getNdefMessage()
                                   throws IOException,
                                          FormatException
        Read the current NdefMessage on this tag.

        This always reads the current NDEF Message stored on the tag.

        Note that this method may return null if the tag was in the INITIALIZED state as defined by NFC Forum, as in that state the tag is formatted to support NDEF but does not contain a message yet.

        This is an I/O operation and will block until complete. It must not be called from the main application thread. A blocked call will be canceled with IOException if close() is called from another thread.

        Requires the android.Manifest.permission#NFC permission.

        Returns:
        the NDEF Message, can be null
        Throws:
        TagLostException - if the tag leaves the field
        IOException - if there is an I/O failure, or the operation is canceled
        FormatException - if the NDEF Message on the tag is malformed
      • writeNdefMessage

        public void writeNdefMessage(NdefMessage msg)
                              throws IOException,
                                     FormatException
        Overwrite the NdefMessage on this tag.

        This is an I/O operation and will block until complete. It must not be called from the main application thread. A blocked call will be canceled with IOException if close() is called from another thread.

        Requires the android.Manifest.permission#NFC permission.

        Parameters:
        msg - the NDEF Message to write, must not be null
        Throws:
        TagLostException - if the tag leaves the field
        IOException - if there is an I/O failure, or the operation is canceled
        FormatException - if the NDEF Message to write is malformed
      • canMakeReadOnly

        public boolean canMakeReadOnly()
        Indicates whether a tag can be made read-only with makeReadOnly().

        Does not cause any RF activity and does not block.

        Returns:
        true if it is possible to make this tag read-only
      • makeReadOnly

        public boolean makeReadOnly()
                             throws IOException
        Make a tag read-only.

        This sets the CC field to indicate the tag is read-only, and where possible permanently sets the lock bits to prevent any further modification of the memory.

        This is a one-way process and cannot be reverted!

        This is an I/O operation and will block until complete. It must not be called from the main application thread. A blocked call will be canceled with IOException if close() is called from another thread.

        Requires the android.Manifest.permission#NFC permission.

        Returns:
        true on success, false if it is not possible to make this tag read-only
        Throws:
        TagLostException - if the tag leaves the field
        IOException - if there is an I/O failure, or the operation is canceled
      • isConnected

        public boolean isConnected()
        Description copied from interface: TagTechnology
        Helper to indicate if I/O operations should be possible.

        Returns true if TagTechnology.connect() has completed, and TagTechnology.close() has not been called, and the Tag is not known to be out of range.

        Does not cause RF activity, and does not block.

        Specified by:
        isConnected in interface TagTechnology
        Returns:
        true if I/O operations should be possible


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