xref: /frameworks/base/docs/html/guide/topics/connectivity/nfc/nfc.jd

page.title=NFC Basics
@jd:body


<div id="qv-wrapper">
<div id="qv">
  <h2>In this document</h2>
  <ol>
    <li><a href="#tag-dispatch">The Tag Dispatch System</a>
      <ol>
        <li><a href="#ndef">How NFC tags are mapped to MIME types and URIs</a></li>
        <li><a href="#dispatching">How NFC Tags are Dispatched to Applications</a></li>
      </ol>
    </li>
    <li><a href="#manifest">Requesting NFC Access in the Android Manifest</a></li>
    <li><a href="#filtering-intents">Filtering for Intents</a>
      <ol>
        <li><a href="#ndef-disc">ACTION_NDEF_DISCOVERED</a></li>
        <li><a href="#tech-disc">ACTION_TECH_DISCOVERED</a></li>
        <li><a href="#tag-disc">ACTION_TAG_DISCOVERED</a></li>
        <li><a href="#obtain-info">Obtaining information from intents</a></li>
      </ol>
    </li>
    <li><a href="#creating-records">Creating Common Types of NDEF Records</a>
      <ol>
        <li><a href="#abs-uri">TNF_ABSOLUTE_URI</a></li>
        <li><a href="#mime">TNF_MIME_MEDIA</a></li>
        <li><a href="#well-known-text">TNF_WELL_KNOWN with RTD_TEXT</a></li>
        <li><a href="#well-known-uri">TNF_WELL_KNOWN with RTD_URI</a></li>
        <li><a href="#ext-type">TNF_EXTERNAL_TYPE</a></li>
        <li><a href="#aar">Android Application Records</a></li>
      </ol>
    </li>
    <li><a href="#p2p">Beaming NDEF Messages to Other Devices</a></li>
  </ol>
</div>
</div>

<p>This document describes the basic NFC tasks you perform in Android. It explains how to send and
receive NFC data in the form of NDEF messages and describes the Android framework APIs that support
these features. For more advanced topics, including a discussion of working with non-NDEF data,
see <a href="{@docRoot}guide/topics/connectivity/nfc/advanced-nfc.html">Advanced NFC</a>.</p>


<p>There are two major uses cases when working with NDEF data and Android:</p>

<ul>
  <li>Reading NDEF data from an NFC tag</li>
  <li>Beaming NDEF messages from one device to another with <a href="#p2p">Android
Beam&trade;</a></li>
</ul>


<p>Reading NDEF data from an NFC tag is handled with the <a href="#tag-dispatch">tag dispatch
system</a>, which analyzes discovered NFC tags, appropriately categorizes the data, and starts
an application that is interested in the categorized data. An application that wants to handle the
scanned NFC tag can <a href="#filtering-intents">declare an intent filter</a> and
request to handle the data.</p>

<p>The Android Beam&trade; feature allows a device to push an NDEF message onto
another device by physically tapping the devices together. This interaction provides an easier way
to send data than other wireless technologies like Bluetooth, because with NFC, no manual device
discovery or pairing is required. The connection is automatically started when two devices come
into range. Android Beam is available through a set of NFC APIs, so any application can transmit
information between devices. For example, the Contacts, Browser, and YouTube applications use
Android Beam to share contacts, web pages, and videos with other devices.
</p>


<h2 id="tag-dispatch">The Tag Dispatch System</h2>

<p>Android-powered devices are usually looking for NFC tags when the screen
is unlocked, unless NFC is disabled in the device's Settings menu.
When an Android-powered device discovers an NFC tag, the desired behavior
is to have the most appropriate activity handle the intent without asking the user what application
to use. Because devices scan NFC tags at a very short range, it is likely that making users manually
select an activity would force them to move the device away from the tag and break the connection.
You should develop your activity to only handle the NFC tags that your activity cares about to
prevent the Activity Chooser from appearing.</p>

<p>To help you with this goal, Android provides a special tag dispatch system that analyzes scanned
NFC tags, parses them, and tries to locate applications that are interested in the scanned data. It
does this by:</p>

<ol>
  <li>Parsing the NFC tag and figuring out the MIME type or a URI that identifies the data payload
  in the tag.</li>
  <li>Encapsulating the MIME type or URI and the payload into an intent. These first two
  steps are described in <a href="#ndef">How NFC tags are mapped to MIME types and URIs</a>.</li>
  <li>Starts an activity based on the intent. This is described in
  <a href="#dispatching">How NFC Tags are Dispatched to Applications</a>.</li>
</ol>

<h3 id="ndef">How NFC tags are mapped to MIME types and URIs</h3>
<p>Before you begin writing your NFC applications, it is important to understand the different
types of NFC tags, how the tag dispatch system parses NFC tags, and the special work that the tag
dispatch system does when it detects an NDEF message. NFC tags come in a
wide array of technologies and can also have data written to them in many different ways.
Android has the most support for the NDEF standard, which is defined by the <a
href="http://www.nfc-forum.org/home">NFC Forum</a>.
</p>

<p>NDEF data is encapsulated inside a message ({@link android.nfc.NdefMessage}) that contains one
or more records ({@link android.nfc.NdefRecord}). Each NDEF record must be well-formed according to
the specification of the type of record that you want to create. Android
also supports other types of tags that do not contain NDEF data, which you can work with by using
the classes in the {@link android.nfc.tech} package. To learn more
about these technologies, see the <a href="{@docRoot}guide/topics/connectivity/nfc/advanced-nfc.html">Advanced
NFC</a> topic. Working with these other types of tags involves
writing your own protocol stack to communicate with the tags, so we recommend using NDEF when
possible for ease of development and maximum support for Android-powered devices.
</p>

<p class="note"><strong>Note:</strong>
To download complete NDEF specifications, go to the <a
href="http://www.nfc-forum.org/specs/spec_license">NFC Forum Specification Download</a> site and see
<a href="#creating-records">Creating common types of NDEF records</a> for examples of how to
construct NDEF records. </p>

<p>Now that you have some background in NFC tags, the following sections describe in more detail how
Android handles NDEF formatted tags. When an Android-powered device scans an NFC tag containing NDEF
formatted data, it parses the message and tries to figure out the data's MIME type or identifying
URI. To do this, the system reads the first {@link android.nfc.NdefRecord} inside the {@link
android.nfc.NdefMessage} to determine how to interpret the entire NDEF message (an NDEF message can
have multiple NDEF records). In a well-formed NDEF message, the first {@link android.nfc.NdefRecord}
contains the following fields:
<dl>
  <dt><strong>3-bit TNF (Type Name Format)</strong></dt>
  <dd>Indicates how to interpret the variable length type field. Valid values are described in
described in <a href="#table1">Table 1</a>.</dd>

  <dt><strong>Variable length type</strong></dt>
  <dd>Describes the type of the record. If using {@link android.nfc.NdefRecord#TNF_WELL_KNOWN}, use
this field to specify the Record Type Definition (RTD). Valid RTD values are described in <a
href="#table2">Table 2</a>.</dd>

<dt><strong>Variable length ID</strong></dt>
<dd>A unique identifier for the record. This field is not used often, but
if you need to uniquely identify a tag, you can create an ID for it.</dd>

<dt><strong>Variable length payload</strong></dt>
<dd>The actual data payload that you want to read or write. An NDEF
message can contain multiple NDEF records, so don't assume the full payload is in the first NDEF
record of the NDEF message.</dd>

</dl>

<p>The tag dispatch system uses the TNF and type fields to try to map a MIME type or URI to the
NDEF message. If successful, it encapsulates that information inside of a {@link
android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intent along with the actual payload. However, there
are cases when the tag dispatch system cannot determine the type of data based on the first NDEF
record. This happens when the NDEF data cannot be mapped to a MIME type or URI, or when the
NFC tag does not contain NDEF data to begin with. In such cases, a {@link
android.nfc.Tag} object that has information about the tag's technologies and the payload are
encapsulated inside of a {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent instead.</p>

<p>
<a href="#table1">Table 1.</a> describes how the tag dispatch system maps TNF and type
fields to MIME types or URIs. It also describes which TNFs cannot be mapped to a MIME type or URI.
In these cases, the tag dispatch system falls back to
{@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.

<p>For example, if the tag dispatch system encounters a record of type {@link
android.nfc.NdefRecord#TNF_ABSOLUTE_URI}, it maps the variable length type field of that record
into a URI. The tag dispatch system encapsulates that URI in the data field of an {@link
android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intent along with other information about the tag,
such as the payload. On the other hand, if it encounters a record of type {@link
android.nfc.NdefRecord#TNF_UNKNOWN}, it creates an intent that encapsulates the tag's technologies
instead.</p>


<p class="table-caption" id="table1">
  <strong>Table 1.</strong> Supported TNFs and their mappings</p>
<table id="mappings">
  <tr>
    <th>Type Name Format (TNF)</th>
    <th>Mapping</th>
  </tr>
  <tr>
    <td>{@link android.nfc.NdefRecord#TNF_ABSOLUTE_URI}</td>
    <td>URI based on the type field.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#TNF_EMPTY}</td>
    <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#TNF_EXTERNAL_TYPE}</td>
    <td>URI based on the URN in the type field. The URN is encoded into the NDEF type field in
        a shortened form: <code><em>&lt;domain_name&gt;:&lt;service_name&gt;</em></code>.
        Android maps this to a URI in the form:
        <code>vnd.android.nfc://ext/<em>&lt;domain_name&gt;:&lt;service_name&gt;</em></code>.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#TNF_MIME_MEDIA}</td>
    <td>MIME type based on the type field.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#TNF_UNCHANGED}</td>
    <td>Invalid in the first record, so falls back to
        {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#TNF_UNKNOWN}</td>
    <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#TNF_WELL_KNOWN}</td>
    <td>MIME type or URI depending on the Record Type Definition (RTD), which you set in the
type field. See <a  href="#well_known">Table 2.</a> for more information on
available RTDs and their mappings.</td>
  </tr>
</table>

<p class="table-caption" id="table2">
  <strong>Table 2.</strong> Supported RTDs for TNF_WELL_KNOWN and their
mappings</p>
<table id="well-known">
  <tr>
    <th>Record Type Definition (RTD)</th>
    <th>Mapping</th>
  </tr>
  <tr>
    <td>{@link android.nfc.NdefRecord#RTD_ALTERNATIVE_CARRIER}</td>
    <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#RTD_HANDOVER_CARRIER}</td>
    <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#RTD_HANDOVER_REQUEST}</td>
    <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#RTD_HANDOVER_SELECT}</td>
    <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#RTD_SMART_POSTER}</td>
    <td>URI based on parsing the payload.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#RTD_TEXT}</td>
    <td>MIME type of <code>text/plain</code>.</td>
  </tr>
    <td>{@link android.nfc.NdefRecord#RTD_URI}</td>
    <td>URI based on payload.</td>
  </tr>
</table>

<h3 id="dispatching">How NFC Tags are Dispatched to Applications</h3>

<p>When the tag dispatch system is done creating an intent that encapsulates the NFC tag and its
identifying information, it sends the intent to an interested application that
filters for the intent. If more than one application can handle the intent, the Activity Chooser
is presented so the user can select the Activity. The tag dispatch system defines three intents,
which are listed in order of highest to lowest priority:</p>

<ol>
  <li>
      {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED}: This intent is used to start an
Activity when a tag that contains an NDEF payload is scanned and is of a recognized type. This is
the highest priority intent, and the tag dispatch system tries to start an Activity with this
intent before any other intent, whenever possible.
  </li>

    <li>{@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}: If no activities register to
handle the {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED}
intent, the tag dispatch system tries to start an application with this intent. This
intent is also directly started (without starting {@link
android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} first) if the tag that is scanned
contains NDEF data that cannot be mapped to a MIME type or URI, or if the tag does not contain NDEF
data but is of a known tag technology.
</li>

    <li>{@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}: This intent is started
    if no activities handle the {@link
android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or {@link
android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}
    intents.</li>
  </ol>

<p>The basic way the tag dispatch system works is as follows:</p>

<ol>
  <li>Try to start an Activity with the intent that was created by the tag dispatch system
when parsing the NFC tag (either
{@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or {@link
android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}).</li>
  <li>If no activities filter for that intent, try to start an Activity with the next
  lowest priority intent (either {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} or {@link
android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}) until an application filters for the
  intent or until the tag dispatch system tries all possible intents.</li>
  <li>If no applications filter for any of the intents, do nothing.</li>
</ol>

<img src="{@docRoot}images/nfc_tag_dispatch.png" />

<p class="figure"><strong>Figure 1. </strong> Tag Dispatch System</p>


<p>Whenever possible, work with NDEF messages and the {@link
android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intent, because it is the most specific out of
the three. This intent allows you to start your application at a more appropriate time than the
other two intents, giving the user a better experience.</p>

<h2 id="manifest">Requesting NFC Access in the Android Manifest</h2>

  <p>Before you can access a device's NFC hardware and properly handle NFC intents, declare these
  items in your <code>AndroidManifest.xml</code> file:</p>

  <ul>
    <li>The NFC <code>&lt;uses-permission&gt;</code> element to access the NFC hardware:
      <pre>
&lt;uses-permission android:name="android.permission.NFC" /&gt;
</pre>
    </li>

    <li>The minimum SDK version that your application can support. API level 9 only supports
    limited tag dispatch via {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}, and only gives
    access to NDEF messages via the {@link android.nfc.NfcAdapter#EXTRA_NDEF_MESSAGES} extra. No
    other tag properties or I/O operations are accessible. API level 10
    includes comprehensive reader/writer support as well as foreground NDEF pushing, and API level
    14 provides an easier way to push NDEF messages to other devices with Android Beam and extra
    convenience methods to create NDEF records.
<pre class="pretty-print">
&lt;uses-sdk android:minSdkVersion="10"/&gt;
</pre>
    </li>

    <li>The <code>uses-feature</code> element so that your application shows up in Google
Play only for devices that have NFC hardware:
      <pre>
&lt;uses-feature android:name="android.hardware.nfc" android:required="true" /&gt;
</pre>
<p>If your application uses NFC functionality, but that functionality is not crucial to your
application, you can omit the <code>uses-feature</code> element and check for NFC avalailbility at
runtime by checking to see if {@link android.nfc.NfcAdapter#getDefaultAdapter getDefaultAdapter()}
is <code>null</code>.</p>
    </li>
  </ul>

  <h2 id="filtering-intents">Filtering for NFC Intents</h2>

  <p>To start your application when an NFC tag that you want to handle is scanned, your application
can filter for one, two, or all three of the NFC intents in the Android manifest. However, you
usually want to filter for the {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intent for the
most control of when your application starts. The {@link
android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent is a fallback for {@link
android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} when no applications filter for
 {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or for when the payload is not
NDEF. Filtering for {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED} is usually too general of a
category to filter on.  Many applications will filter for {@link
android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or {@link
android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} before {@link
android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}, so your application has a low probability of
starting. {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED} is only available as a last resort
for applications to filter for in the cases where no other applications are installed to handle the
{@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or {@link
android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}intent.</p>

<p>Because NFC tag deployments vary and are many times not under your control, this is not always
possible, which is why you can fallback to the other two intents when necessary. When you have
control over the types of tags and data written, it is recommended that you use NDEF to format your
tags. The following sections describe how to filter for each type of intent.</p>


<h3 id="ndef-disc">ACTION_NDEF_DISCOVERED</h3>
<p>
To filter for {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intents, declare the
intent filter along with the type of data that you want to filter for. The
following example filters for {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED}
intents with a MIME type of <code>text/plain</code>:
</p>
<pre>
&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.NDEF_DISCOVERED"/&gt;
    &lt;category android:name="android.intent.category.DEFAULT"/&gt;
    &lt;data android:mimeType="text/plain" /&gt;
&lt;/intent-filter&gt;
</pre>
<p>The following example filters for a URI in the form of
<code>http://developer.android.com/index.html</code>.
<pre>
&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.NDEF_DISCOVERED"/&gt;
    &lt;category android:name="android.intent.category.DEFAULT"/&gt;
   &lt;data android:scheme="http"
              android:host="developer.android.com"
              android:pathPrefix="/index.html" />
&lt;/intent-filter&gt;
</pre>


  <h3 id="tech-disc">ACTION_TECH_DISCOVERED</h3>

  <p>If your activity filters for the {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent,
you must create an XML resource file that specifies the technologies that your activity supports
within a <code>tech-list</code> set. Your activity is
  considered a match if a <code>tech-list</code> set is a subset of the technologies that are
  supported by the tag, which you can obtain by calling {@link android.nfc.Tag#getTechList
  getTechList()}.</p>

  <p>For example, if the tag that is scanned supports MifareClassic, NdefFormatable, and NfcA, your
  <code>tech-list</code> set must specify all three, two, or one of the technologies (and nothing
  else) in order for your activity to be matched.</p>

  <p>The following sample defines all of the technologies. You can remove the ones that you do not
  need. Save this file (you can name it anything you wish) in the
  <code>&lt;project-root&gt;/res/xml</code> folder.</p>
  <pre>
&lt;resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"&gt;
    &lt;tech-list&gt;
        &lt;tech&gt;android.nfc.tech.IsoDep&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.NfcA&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.NfcB&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.NfcF&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.NfcV&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.Ndef&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.NdefFormatable&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.MifareClassic&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.MifareUltralight&lt;/tech&gt;
    &lt;/tech-list&gt;
&lt;/resources&gt;
</pre>

  <p>You can also specify multiple <code>tech-list</code> sets. Each of the <code>tech-list</code>
  sets is considered independently, and your activity is considered a match if any single
  <code>tech-list</code> set is a subset of the technologies that are returned by {@link
  android.nfc.Tag#getTechList getTechList()}. This provides <code>AND</code> and <code>OR</code>
  semantics for matching technologies. The following example matches tags that can support the
  NfcA and Ndef technologies or can support the NfcB and Ndef technologies:</p>
  <pre>
&lt;resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"&gt;
    &lt;tech-list&gt;
        &lt;tech&gt;android.nfc.tech.NfcA&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.Ndef&lt;/tech&gt;
    &lt;/tech-list&gt;
&lt;/resources&gt;

&lt;resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"&gt;
    &lt;tech-list&gt;
        &lt;tech&gt;android.nfc.tech.NfcB&lt;/tech&gt;
        &lt;tech&gt;android.nfc.tech.Ndef&lt;/tech&gt;
    &lt;/tech-list&gt;
&lt;/resources&gt;
</pre>

  <p>In your <code>AndroidManifest.xml</code> file, specify the resource file that you just created
  in the <code>&lt;meta-data&gt;</code> element inside the <code>&lt;activity&gt;</code>
  element like in the following example:</p>
  <pre>
&lt;activity&gt;
...
&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.TECH_DISCOVERED"/&gt;
&lt;/intent-filter&gt;

&lt;meta-data android:name="android.nfc.action.TECH_DISCOVERED"
    android:resource="@xml/nfc_tech_filter" /&gt;
...
&lt;/activity&gt;
</pre>

<p>For more information about working with tag technologies and the {@link
android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent, see <a
href="{@docRoot}guide/topics/connectivity/nfc/advanced-nfc.html#tag-tech">Working with Supported Tag
Technologies</a> in the Advanced NFC document.</p>
<h3 id="tag-disc">ACTION_TAG_DISCOVERED</h3>
<p>To filter for {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED} use the following intent
filter:</p>


<pre>&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.TAG_DISCOVERED"/&gt;
&lt;/intent-filter&gt;
</pre>



<h3 id="obtain-info">Obtaining information from intents</h3>

<p>If an activity starts because of an NFC intent, you can obtain information about the scanned NFC
tag from the intent. Intents can contain the following extras depending on the tag that was scanned:

<ul>
  <li>{@link android.nfc.NfcAdapter#EXTRA_TAG} (required): A {@link android.nfc.Tag} object
representing the scanned tag.</li>
  <li>{@link android.nfc.NfcAdapter#EXTRA_NDEF_MESSAGES} (optional): An array of NDEF messages
parsed from the tag. This extra is mandatory on {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED
intents.</li>
  <li>{@link android.nfc.NfcAdapter#EXTRA_ID} (optional): The low-level ID of the tag.</li></ul>

<p>To obtain these extras, check to see if your activity was launched with one of
the NFC intents to ensure that a tag was scanned, and then obtain the extras out of the
intent. The following example checks for the {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED}
intent and gets the NDEF messages from an intent extra.</p>

<pre>
public void onResume() {
    super.onResume();
    ...
    if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) {
        Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
        if (rawMsgs != null) {
            msgs = new NdefMessage[rawMsgs.length];
            for (int i = 0; i &lt; rawMsgs.length; i++) {
                msgs[i] = (NdefMessage) rawMsgs[i];
            }
        }
    }
    //process the msgs array
}
</pre>

<p>Alternatively, you can obtain a {@link android.nfc.Tag} object from the intent, which will
contain the payload and allow you to enumerate the tag's technologies:</p>

<pre>Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);</pre>


<h2 id="creating-records">Creating Common Types of NDEF Records</h2>
<p>This section describes how to create common types of NDEF records to help you when writing to
NFC tags or sending data with Android Beam. It also describes how to create the corresponding
intent filter for the record. All of these NDEF record examples should be in the first NDEF
record of the NDEF message that you are writing to a tag or beaming.</p>

<h3 id="abs-uri">TNF_ABSOLUTE_URI</h3>
<p>Given the following {@link android.nfc.NdefRecord#TNF_ABSOLUTE_URI} NDEF record, which is
stored as the first record inside of an {@link android.nfc.NdefMessage}:</p>

<pre>
NdefRecord uriRecord = new NdefRecord(
    NdefRecord.TNF_ABSOLUTE_URI ,
    "http://developer.android.com/index.html".getBytes(Charset.forName("US-ASCII")),
    new byte[0], new byte[0]);
</pre>

<p>the intent filter would look like this:</p>
<pre>
&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.NDEF_DISCOVERED" /&gt;
    &lt;category android:name="android.intent.category.DEFAULT" /&gt;
    &lt;data android:scheme="http"
        android:host="developer.android.com"
        android:pathPrefix="/index.html" /&gt;
&lt;/intent-filter&gt;
</pre>


<h3 id="mime">TNF_MIME_MEDIA</h3>
<p>Given the following {@link android.nfc.NdefRecord#TNF_MIME_MEDIA} NDEF record, which is stored as
the first record inside
of an {@link android.nfc.NdefMessage}:</p>
<pre>
NdefRecord mimeRecord = new NdefRecord(
    NdefRecord.TNF_MIME_MEDIA ,
    "application/com.example.android.beam".getBytes(Charset.forName("US-ASCII")),
    new byte[0], "Beam me up, Android!".getBytes(Charset.forName("US-ASCII")));
</pre>

<p>the intent filter would look like this:</p>
<pre>
&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.NDEF_DISCOVERED" /&gt;
    &lt;category android:name="android.intent.category.DEFAULT" /&gt;
    &lt;data android:mimeType="application/com.example.android.beam" /&gt;
&lt;/intent-filter&gt;
</pre>


<h3 id="well-known-text">TNF_WELL_KNOWN with RTD_TEXT</h3>

<p>Given the following {@link android.nfc.NdefRecord#TNF_WELL_KNOWN} NDEF record, which is stored as
the first record inside of an {@link android.nfc.NdefMessage}:</p>
<pre>
public NdefRecord createTextRecord(String payload, Locale locale, boolean encodeInUtf8) {
    byte[] langBytes = locale.getLanguage().getBytes(Charset.forName("US-ASCII"));
    Charset utfEncoding = encodeInUtf8 ? Charset.forName("UTF-8") : Charset.forName("UTF-16");
    byte[] textBytes = payload.getBytes(utfEncoding);
    int utfBit = encodeInUtf8 ? 0 : (1 &lt;&lt; 7);
    char status = (char) (utfBit + langBytes.length);
    byte[] data = new byte[1 + langBytes.length + textBytes.length];
    data[0] = (byte) status;
    System.arraycopy(langBytes, 0, data, 1, langBytes.length);
    System.arraycopy(textBytes, 0, data, 1 + langBytes.length, textBytes.length);
    NdefRecord record = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,
    NdefRecord.RTD_TEXT, new byte[0], data);
    return record;
}
</pre>

<p>the intent filter would look like this:</p>
<pre>
&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.NDEF_DISCOVERED" /&gt;
    &lt;category android:name="android.intent.category.DEFAULT" /&gt;
    &lt;data android:mimeType="text/plain" /&gt;
&lt;/intent-filter&gt;
</pre>


<h3 id="well-known-uri">TNF_WELL_KNOWN with RTD_URI</h3>

<p>Given the following {@link android.nfc.NdefRecord#TNF_WELL_KNOWN} NDEF record, which is stored as
the first record inside of an {@link android.nfc.NdefMessage}:</p>

<pre>
byte[] uriField = "example.com".getBytes(Charset.forName("US-ASCII"));
byte[] payload = new byte[uriField.length + 1];              //add 1 for the URI Prefix
byte payload[0] = 0x01;                                      //prefixes http://www. to the URI
System.arraycopy(uriField, 0, payload, 1, uriField.length);  //appends URI to payload
NdefRecord rtdUriRecord = new NdefRecord(
    NdefRecord.TNF_WELL_KNOWN, NdefRecord.RTD_URI, new byte[0], payload);
</pre>

<p>the intent filter would look like this:</p>

<pre>
&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.NDEF_DISCOVERED" /&gt;
    &lt;category android:name="android.intent.category.DEFAULT" /&gt;
    &lt;data android:scheme="http"
        android:host="example.com"
        android:pathPrefix="" /&gt;
&lt;/intent-filter&gt;
</pre>

<h3 id="ext-type">TNF_EXTERNAL_TYPE</h3>
<p>Given the following {@link android.nfc.NdefRecord#TNF_EXTERNAL_TYPE} NDEF record, which is stored
as the first record inside of an {@link android.nfc.NdefMessage}:</p>

<pre>
byte[] payload;
...
NdefRecord mimeRecord = new NdefRecord(
    NdefRecord.TNF_EXTERNAL_TYPE, "example.com:externalType", new byte[0], payload);
</pre>

<p>the intent filter would look like this:</p>
<pre>
&lt;intent-filter&gt;
    &lt;action android:name="android.nfc.action.NDEF_DISCOVERED" /&gt;
    &lt;category android:name="android.intent.category.DEFAULT" /&gt;
    &lt;data android:scheme="vnd.android.nfc"
        android:host="ext"
        android:pathPrefix="/example.com:externalType"/&gt;
&lt;/intent-filter&gt;
</pre>


<p>Use TNF_EXTERNAL_TYPE for more generic NFC tag deployments to better support both
Android-powered and non-Android-powered devices.</p>

<p class="note"><strong>Note</strong>: URNs for {@link
android.nfc.NdefRecord#TNF_EXTERNAL_TYPE} have a canonical format of:
<code>urn:nfc:ext:example.com:externalType</code>, however the NFC Forum RTD specification
declares that the <code>urn:nfc:ext:</code> portion of the URN must be ommitted from the
NDEF record. So all you need to provide is the domain (<code>example.com</code> in the example)
and type (<code>externalType</code> in the example) separated by a colon.
When dispatching TNF_EXTERNAL_TYPE, Android converts the <code>urn:nfc:ext:example.com:externalType</code> URN to a
<code>vnd.android.nfc://ext/example.com:externalType</code> URI, which is what the intent filter in the example
declares.</p>

<h3 id="aar">Android Application Records</h3>

<p>
Introduced in Android 4.0 (API level 14), an Android Application Record (AAR) provides a stronger
certainty that your application is started when an NFC tag is scanned. An AAR has the package name
of an application embedded inside an NDEF record. You can add an AAR to any NDEF record of your NDEF message,
because Android searches the entire NDEF message for AARs. If it finds an AAR, it starts the application based
on the package name inside the AAR. If the application is not present on the device,
Google Play is launched to download the application.</p>

<p>AARs are useful if you want to prevent other applications from filtering for the same intent and
potentially handling specific tags that you have deployed. AARs are only supported at the
application level, because of the package name constraint, and not at the Activity level as with
intent filtering. If you want to handle an intent at the Activity level, <a
href="#filtering-intents">use intent filters</a>.
</p>



<p>If a tag contains an AAR, the tag dispatch system dispatches in the following manner:</p>
<ol>
  <li>Try to start an Activity using an intent filter as normal. If the Activity that matches
the intent also matches the AAR, start the Activity.</li>
  <li>If the Activity that filters for the intent does not match the
AAR, if multiple Activities can handle the intent, or if no Activity handles the intent, start the
application specified by the AAR.</li>
  <li>If no application can start with the AAR, go to Google Play to download the
application based on the AAR.</li>
</ol>

</p>

<p class="note"><strong>Note:</strong> You can override AARs and the intent dispatch system with the <a
href="{@docRoot}guide/topics/connectivity/nfc/advanced-nfc.html#foreground-dispatch">foreground dispatch
system</a>, which allows a foreground activity to have priority when an NFC tag is discovered.
With this method, the activity must be in the foreground to
override AARs and the intent dispatch system.</p>

<p>If you still want to filter for scanned tags that do not contain an AAR, you can declare
intent filters as normal. This is useful if your application is interested in other tags
that do not contain an AAR. For example, maybe you want to guarantee that your application handles
proprietary tags that you deploy as well as general tags deployed by third parties. Keep in mind
that AARs are specific to Android 4.0 devices or later, so when deploying tags, you most likely want
to use a combination of AARs and MIME types/URIs to support the widest range of devices. In
addition, when you deploy NFC tags, think about how you want to write your NFC tags to enable
support for the most devices (Android-powered and other devices). You can do this by
defining a relatively unique MIME type or URI to make it easier for applications to distinguish.
</p>

<p>Android provides a simple API to create an AAR,
{@link android.nfc.NdefRecord#createApplicationRecord createApplicationRecord()}. All you need to
do is embed the AAR anywhere in your {@link android.nfc.NdefMessage}. You do not want
to use the first record of your {@link android.nfc.NdefMessage}, unless the AAR is the only
record in the {@link android.nfc.NdefMessage}. This is because the Android
system checks the first record of an {@link android.nfc.NdefMessage} to determine the MIME type or
URI of the tag, which is used to create an intent for applications to filter. The following code
shows you how to create an AAR:</p>

<pre>
NdefMessage msg = new NdefMessage(
        new NdefRecord[] {
            ...,
            NdefRecord.createApplicationRecord("com.example.android.beam")}
</pre>


<h2 id="p2p">Beaming NDEF Messages to Other Devices</h2>

<p>Android Beam allows simple peer-to-peer data exchange between two Android-powered devices. The
application that wants to beam data to another device must be in the foreground and the device
receiving the data must not be locked. When the beaming device comes in close enough contact with a
receiving device, the beaming device displays the "Touch to Beam" UI. The user can then choose
whether or not to beam the message to the receiving device.</p>

<p class="note"><strong>Note:</strong> Foreground NDEF pushing was available at API level 10,
which provides similar functionality to Android Beam. These APIs have since been deprecated, but
are available to support older devices. See {@link android.nfc.NfcAdapter#enableForegroundNdefPush
enableForegroundNdefPush()} for more information.</p>

<p>You can enable Android Beam for your application by calling one of the two methods:</p>
  <ul>
    <li>{@link android.nfc.NfcAdapter#setNdefPushMessage setNdefPushMessage()}: Accepts an
{@link android.nfc.NdefMessage} to set as the message to beam. Automatically beams the message
when two devices are in close enough proximity.</li>
    <li>{@link android.nfc.NfcAdapter#setNdefPushMessageCallback setNdefPushMessageCallback()}:
Accepts a callback that contains a
{@link android.nfc.NfcAdapter.CreateNdefMessageCallback#createNdefMessage createNdefMessage()}
which is called when a device is in range to beam data to. The callback lets you create
the NDEF message only when necessary.</li>
  </ul>

<p>An activity can only push one NDEF message at a time, so {@link
android.nfc.NfcAdapter#setNdefPushMessageCallback setNdefPushMessageCallback()} takes precedence
over {@link android.nfc.NfcAdapter#setNdefPushMessage setNdefPushMessage()} if both are set. To use
Android Beam, the following general guidelines must be met:
</p>

  <ul>
    <li>The activity that is beaming the data must be in the foreground. Both devices must have
their screens unlocked.</li>

    <li>You must encapsulate the data that you are beaming in an {@link android.nfc.NdefMessage}
    object.</li>

    <li>The NFC device that is receiving the beamed data must support the
    <code>com.android.npp</code> NDEF push protocol or NFC Forum's SNEP (Simple NDEF Exchange
Protocol). The <code>com.android.npp</code> protocol is required for devices on API level 9 (Android
2.3) to API level 13 (Android 3.2). <code>com.android.npp</code> and SNEP are both required on
API level 14 (Android 4.0) and later.</li>
</li>
  </ul>

  <p class="note"><strong>Note:</strong> If your activity enables Android Beam and is
in the foreground, the standard intent dispatch system is disabled. However, if your activity also
enables <a href="{@docRoot}guide/topics/connectivity/nfc/advanced-nfc.html#foreground-dispatch">foreground
dispatching</a>, then it can still scan tags that match the intent filters set in the foreground
dispatching.</p>

  <p>To enable Android Beam:</p>

  <ol>
    <li>Create an {@link android.nfc.NdefMessage} that contains the {@link android.nfc.NdefRecord}s
that you want to push onto the other device.</li>

    <li>Call {@link
android.nfc.NfcAdapter#setNdefPushMessage setNdefPushMessage()} with a {@link
android.nfc.NdefMessage} or call {@link
android.nfc.NfcAdapter#setNdefPushMessageCallback setNdefPushMessageCallback} passing in a {@link
android.nfc.NfcAdapter.CreateNdefMessageCallback} object in the <code>onCreate()</code> method of
your activity. These methods require at least one activity that you want to enable with Android
Beam, along with an optional list of other activities to activate.

<p>In general, you normally use {@link
android.nfc.NfcAdapter#setNdefPushMessage setNdefPushMessage()} if your Activity only needs to
push the same NDEF message at all times, when two devices are in range to communicate. You use
{@link android.nfc.NfcAdapter#setNdefPushMessageCallback setNdefPushMessageCallback} when your
application cares about the current context of the application and wants to push an NDEF message
depending on what the user is doing in your application.</p>
    </li>
  </ol>

<p>The following sample shows how a simple activity calls {@link
android.nfc.NfcAdapter.CreateNdefMessageCallback} in the <code>onCreate()</code> method of an
activity (see <a href="{@docRoot}resources/samples/AndroidBeamDemo/index.html">AndroidBeamDemo</a>
for the complete sample). This example also has methods to help you create a MIME record:</p>

<pre id="code-example">
package com.example.android.beam;

import android.app.Activity;
import android.content.Intent;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.NfcAdapter.CreateNdefMessageCallback;
import android.nfc.NfcEvent;
import android.os.Bundle;
import android.os.Parcelable;
import android.widget.TextView;
import android.widget.Toast;
import java.nio.charset.Charset;


public class Beam extends Activity implements CreateNdefMessageCallback {
    NfcAdapter mNfcAdapter;
    TextView textView;

    &#064;Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TextView textView = (TextView) findViewById(R.id.textView);
        // Check for available NFC Adapter
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if (mNfcAdapter == null) {
            Toast.makeText(this, "NFC is not available", Toast.LENGTH_LONG).show();
            finish();
            return;
        }
        // Register callback
        mNfcAdapter.setNdefPushMessageCallback(this, this);
    }

    &#064;Override
    public NdefMessage createNdefMessage(NfcEvent event) {
        String text = ("Beam me up, Android!\n\n" +
                "Beam Time: " + System.currentTimeMillis());
        NdefMessage msg = new NdefMessage(
                new NdefRecord[] { createMimeRecord(
                        "application/com.example.android.beam", text.getBytes())
         /**
          * The Android Application Record (AAR) is commented out. When a device
          * receives a push with an AAR in it, the application specified in the AAR
          * is guaranteed to run. The AAR overrides the tag dispatch system.
          * You can add it back in to guarantee that this
          * activity starts when receiving a beamed message. For now, this code
          * uses the tag dispatch system.
          */
          //,NdefRecord.createApplicationRecord("com.example.android.beam")
        });
        return msg;
    }

    &#064;Override
    public void onResume() {
        super.onResume();
        // Check to see that the Activity started due to an Android Beam
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) {
            processIntent(getIntent());
        }
    }

    &#064;Override
    public void onNewIntent(Intent intent) {
        // onResume gets called after this to handle the intent
        setIntent(intent);
    }

    /**
     * Parses the NDEF Message from the intent and prints to the TextView
     */
    void processIntent(Intent intent) {
        textView = (TextView) findViewById(R.id.textView);
        Parcelable[] rawMsgs = intent.getParcelableArrayExtra(
                NfcAdapter.EXTRA_NDEF_MESSAGES);
        // only one message sent during the beam
        NdefMessage msg = (NdefMessage) rawMsgs[0];
        // record 0 contains the MIME type, record 1 is the AAR, if present
        textView.setText(new String(msg.getRecords()[0].getPayload()));
    }

    /**
     * Creates a custom MIME type encapsulated in an NDEF record
     */
    public NdefRecord createMimeRecord(String mimeType, byte[] payload) {
        byte[] mimeBytes = mimeType.getBytes(Charset.forName("US-ASCII"));
        NdefRecord mimeRecord = new NdefRecord(
                NdefRecord.TNF_MIME_MEDIA, mimeBytes, new byte[0], payload);
        return mimeRecord;
    }
}
</pre>

<p>Note that this code comments out an AAR, which you can remove. If you enable the AAR, the
application specified in the AAR always receives the Android Beam message. If the application is not
present, Google Play launches to download the application. Therefore, the following intent
filter is not technically necessary for Android 4.0 devices or later if the AAR is used:
</p>

<pre>
&lt;intent-filter&gt;
  &lt;action android:name="android.nfc.action.NDEF_DISCOVERED"/&gt;
  &lt;category android:name="android.intent.category.DEFAULT"/&gt;
  &lt;data android:mimeType="application/com.example.android.beam"/&gt;
&lt;/intent-filter&gt;
</pre>
<p>With this intent filter, the <code>com.example.android.beam</code> application now can be started
when it scans an NFC tag or receives an Android Beam with an AAR of
type <code>com.example.android.beam</code>, or when an NDEF formatted message contains a MIME record
of type <code>application/com.example.android.beam</code>.</p>

<p>Even though AARs guarantee an application is started or downloaded, intent filters are
recommended, because they let you start an Activity of your choice in your
application instead of always starting the main Activity within the package specified by an AAR.
AARs do not have Activity level granularity. Also, because some Android-powered devices do not
support AARs, you should also embed identifying information in the first NDEF record of your NDEF
messages and filter for that as well, just in case. See <a href="#creating-records">Creating Common
Types of NDEF records</a> for more information on how to create records.
</p>