java.lang.Object | |
↳ | android.nfc.Tag |
Represents an NFC tag that has been discovered.
Tag
is an immutable object that represents the state of a NFC tag at
the time of discovery. It can be used as a handle to TagTechnology
classes
to perform advanced operations, or directly queried for its ID via getId()
and the
set of technologies it contains via getTechList()
. Arrays passed to and
returned by this class are not cloned, so be careful not to modify them.
A new tag object is created every time a tag is discovered (comes into range), even
if it is the same physical tag. If a tag is removed and then returned into range, then
only the most recent tag object can be successfully used to create a TagTechnology
.
Tag
object is created and passed to a
single activity via the EXTRA_TAG
extra in an
Intent
via startActivity(Intent)
. A four stage dispatch is used
to select the
most appropriate activity to handle the tag. The Android OS executes each stage in order,
and completes dispatch as soon as a single matching activity is found. If there are multiple
matching activities found at any one stage then the Android activity chooser dialog is shown
to allow the user to select the activity to receive the tag.
The Tag dispatch mechanism was designed to give a high probability of dispatching a tag to the correct activity without showing the user an activity chooser dialog. This is important for NFC interactions because they are very transient -- if a user has to move the Android device to choose an application then the connection will likely be broken.
NfcAdapter.enableForegroundDispatch()
is
given priority. See the documentation on
NfcAdapter.enableForegroundDispatch()
for
its usage.
NdefRecord
in the first
NdefMessage
. If the record is a URI, SmartPoster, or MIME data
startActivity(Intent)
is called with ACTION_NDEF_DISCOVERED
. For URI
and SmartPoster records the URI is put into the intent's data field. For MIME records the MIME
type is put in the intent's type field. This allows activities to register to be launched only
when data they know how to handle is present on a tag. This is the preferred method of handling
data on a tag since NDEF data can be stored on many types of tags and doesn't depend on a
specific tag technology.
See ACTION_NDEF_DISCOVERED
for more detail. If the tag does not contain
NDEF data, or if no activity is registered
for ACTION_NDEF_DISCOVERED
with a matching data URI or MIME type then dispatch
moves to stage 3.
startActivity(Intent)
is called with ACTION_TECH_DISCOVERED
to
dispatch the tag to an activity that can handle the technologies present on the tag.
Technologies are defined as sub-classes of TagTechnology
, see the package
android.nfc.tech
. The Android OS looks for an activity that can handle one or
more technologies in the tag. See ACTION_TECH_DISCOVERED
for more detail.
startActivity(Intent)
is called with
ACTION_TAG_DISCOVERED
. This is intended as a fall-back mechanism.
See ACTION_TAG_DISCOVERED
.
Tags can have a wide range of capabilities. Simple tags just offer read/write semantics,
and contain some one time
programmable areas to make read-only. More complex tags offer math operations
and per-sector access control and authentication. The most sophisticated tags
contain operating environments allowing complex interactions with the
code executing on the tag. Use TagTechnology
classes to access a broad
range of capabilities available in NFC tags.
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Inherited Constants | |||||||||||
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From interface
android.os.Parcelable
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Fields | |||||||||||
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CREATOR |
Public Methods | |||||||||||
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Describe the kinds of special objects contained in this Parcelable's
marshalled representation.
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Get the Tag Identifier (if it has one).
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Get the technologies available in this tag, as fully qualified class names.
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Human-readable description of the tag, for debugging.
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Flatten this object in to a Parcel.
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Inherited Methods | |||||||||||
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From class
java.lang.Object
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From interface
android.os.Parcelable
|
Describe the kinds of special objects contained in this Parcelable's marshalled representation.
Get the Tag Identifier (if it has one).
The tag identifier is a low level serial number, used for anti-collision and identification.
Most tags have a stable unique identifier (UID), but some tags will generate a random ID every time they are discovered (RID), and there are some tags with no ID at all (the byte array will be zero-sized).
The size and format of an ID is specific to the RF technology used by the tag.
This function retrieves the ID as determined at discovery time, and does not perform any further RF communication or block.
Get the technologies available in this tag, as fully qualified class names.
A technology is an implementation of the TagTechnology
interface,
and can be instantiated by calling the static get(Tag)
method on the implementation with this Tag. The TagTechnology
object can then be used to perform advanced, technology-specific operations on a tag.
Android defines a mandatory set of technologies that must be correctly
enumerated by all Android NFC devices, and an optional
set of proprietary technologies.
See TagTechnology
for more details.
The ordering of the returned array is undefined and should not be relied upon.
TagTechnology
class-names.
Human-readable description of the tag, for debugging.
Flatten this object in to a Parcel.
dest | The Parcel in which the object should be written. |
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flags | Additional flags about how the object should be written.
May be 0 or PARCELABLE_WRITE_RETURN_VALUE .
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