Near field communication (NFC) in android

Presenter: Jitendra Singh, Mindfire Solutions
Date: 12/feb/2015
NEAR FIELD COMMUNICATION

About Me
Jitendra Singh
Senior Android Developer
Mindfire Solutions
Skills: AndroidApplicationDevelopment, Blackberry,PhoneGap,
Struts, Hibernate, Servlets, JSP, J2EE, Apache, CoreJava,
SQL, SQLite, SQLServer, J2ME, JasperReport,NFC
Skype: mfsi_jitendra.singh
Email:jitendra.singh@mindfiresolutions.com

AGENDA
1) What is NFC?
2) Classes available in Android to use NFC
3) NDEF Structure
4) Tag Intent Dispatch System
5) NFC Intents
6) Filtering for NFC Intents
7) How to check whether a device supports NFC or not
8) NFC Tag Reading/Writing
9) Android Application Record

1) NFC is a high frequency short-range wireless communication technology that enables the exchange of
data between devices over about a 10 cm distance.
2) Near-field communication uses electromagnetic induction between two loop antennas located within each
others near field.
3) Android-powered devices with NFC mainly support two main modes of operation:
a) Reader/writer mode, allowing the NFC device to read and/or write passive NFC tags and stickers.
b) P2P mode, allowing the NFC device to exchange data with other NFC peers; this operation mode is
used by Android Beam.

1) NFC-related APIs in Android are introduced to users starting from API level 9.
2) Currently, there are two packages for NFC application development in the Android platform.
a) The first is the main package that you will use is android.nfc, which includes
necessary classes to enable applications to read and write NDEF messages
in/to NFC tags.
b) The second is the android.nfc.tech package, which includes necessary classes
to provide access to different tag technologies such as MIFARE Classic, NfcA
, NfcV, and so on.
Continued........

CLASS NAME DESCRIPTION
Tag Represents the discovered NFC tag
NfcAdapter Represents the NFC adapter of the
mobile phone
NfcManager Obtains an instance of the NFC adapter
NdefMessage Represents an NDEF message
NdefRecord Represents an NDEF record
Classes available in the android.nfc package are as follows

1) All the messages that are transferred between two android devices or between devices or a
NFC tag are mostly transferred in NDEF format.
2) NDEF is a binary format structured in messages, each of which can contain several records.
3) Each record is made up of a header, which contains meta data about the record, such as the
record type,length, and so forth, and the payload, which contains the content of the message.
Continued........

4) An NDEF record consists of a type name format (TNF), payload type, payload identifier, and the
payload.
5) The TNF tells you how to interpret the payload type. The payload type is an NFC-specific type,
MIME mediatype, or URI that tells you how to interpret the payload.
6) Another way to think about this is that the TNF is the metadata about the payload type, and the
payload type is the metadata about the payload.

1) The tag intent dispatch system is used to launch applications when the predefined tags or NDEF
data are identified in tags.
2) In short, you scan to an NFC tag, and if any application is registered to handle the tag, then the
registered application launches.
3) If more than one application is registered to handle the tag, a pop-up to select the application
(Activity Chooser) is displayed.
4)When an NFC tag is discovered in proximity, the type and payload data in the tag will be
encapsulated to intent, and the tag intent dispatch system in Android will run the corresponding
application that can handle the tag.
Continued........

ACTION_NDEF_DISCOVERED
The tag dispatch system uses the TNF and Type fields to try to map a known MIME type or URI to the NDEF message. If
successful, it encapsulates that information inside of a ACTION_NDEF_DISCOVERED intent along with the actual
payload.
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.
ACTION_TECH_DISCOVERED
If 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.
In such cases, a Tag object that has information about the tag's technologies and the payload are encapsulated inside of
a ACTION_TECH_DISCOVERED intent.
ACTION_TAG_DISCOVERED
This intent has the lowest priority. If no activities in the device can handle the corresponding above intents, then
ACTION_TAG_DISCOVERED is created.
Continued........

1)The tag dispatch system works as follows:
➤ If the payload contains NDEF data:
1. Try to start an activity with the ACTION_NDEF_DISCOVERED intent.
2. If no activities filter for the discovered NDEF data, try to start an activity with the
the ACTION_TECH_DISCOVERED intent.
➤ If the payload does not contain NDEF data but is of a known tag technology:
1. Try to start an activity with the ACTION_TECH_DISCOVERED intent.
2. If no activities filter for that intent, try to start an activity with the ACTION_TAG_DISCOVERED intent.
There are 3 types of NFC intents viz :
1) ACTION_NDEF_DISCOVERED
2) ACTION_TECH_DISCOVERED
3) ACTION_TAG_DISCOVERED

Filtering for ACTION_NDEF_DISCOVERED
This concept would be best explained by examples
Example 1
<intent-filter>
<action android:name="android.nfc.action.NDEF_DISCOVERED"/>
<category android:name="android.intent.category.DEFAULT"/>
<data android:mimeType="text/plain" />
</intent-filter>
Example 2
<intent-filter>
<action android:name="android.nfc.action.NDEF_DISCOVERED"/>
<category android:name="android.intent.category.DEFAULT"/>
<data android:scheme="http"
android:host="developer.android.com"
android:pathPrefix="/index.html" />
</intent-filter>
Continued........

Filtering for ACTION_TECH_DISCOVERED
If your activity filters for the ACTION_TECH_DISCOVERED intent, you must create an XML resource file that specifies the
technologies that your activity supports within a tech-list set. Your activity is considered a match if a tech-list set is a subset of
the technologies that are supported by the tag.
Example
<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
<tech-list>
<tech>android.nfc.tech.IsoDep</tech>
<tech>android.nfc.tech.NfcA</tech>
<tech>android.nfc.tech.NfcB</tech>
<tech>android.nfc.tech.NfcF</tech>
<tech>android.nfc.tech.NfcV</tech>
<tech>android.nfc.tech.Ndef</tech>
<tech>android.nfc.tech.NdefFormatable</tech>
<tech>android.nfc.tech.MifareClassic</tech>
<tech>android.nfc.tech.MifareUltralight</tech>
</tech-list>
</resources>
In your AndroidManifest.xml file, specify the resource file that you just created in the <meta-data> element inside the
<activity> element like in the following example:
<activity>
<intent-filter>
<action android:name="android.nfc.action.TECH_DISCOVERED"/>
</intent-filter>
<meta-data android:name="android.nfc.action.TECH_DISCOVERED"
android:resource="@xml/nfc_tech_filter" />
</activity>

Filtering for ACTION_TECH_DISCOVERED
To filter for ACTION_TAG_DISCOVERED use the following intent filter:
<intent-filter>
<action android:name="android.nfc.action.TAG_DISCOVERED"/>
</intent-filter>

How to check whether a device supports NFC or not
The NFCAdapter class in the android.nfc package represents the NFC adapter for the local machine.
Checking if the NFCAdapter is available is the first thing to do in an NFC application. Here is the code to
create the necessary NfcAdapter:
private NfcAdapter myNfcAdapter;
private TextView myText;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
myNfcAdapter = NfcAdapter.getDefaultAdapter(this);
if (myNfcAdapter == null)
{
myText.setText("NFC is not available for the device!!!");
}
else
{
myText.setText("NFC is available for the device");
}
}

How to check whether a device supports NFC or not
The NFCAdapter class in the android.nfc package represents the NFC adapter for the device. Checking if
the NFCAdapter is available is the first thing to do in an NFC application. Here is the code to create the
necessary NfcAdapter:
private NfcAdapter myNfcAdapter;
private TextView myText;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
myNfcAdapter = NfcAdapter.getDefaultAdapter(this);
if (myNfcAdapter == null)
{
myText.setText("NFC is not available for the device!!!");
}
else
{
myText.setText("NFC is available for the device");
}
}

8) NFC Tag Writing
In the following code, the basic write operation to a tag is shown, in which the discovered tag has NDEF
payload.
if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction()))
{
Tag detectedTag = getIntent().getParcelableExtra(NfcAdapter.EXTRA_TAG);
Ndef ndef = Ndef.get(detectedTag);
//If ndef object is null it means that the tag is not NDEF-formatted and you cannot use Ndef class.
//If it is already NDEF-formatted, you will use Ndef class; otherwise, you need to use NdefFormatable
//class with following code
If(ndef == null)
NdefFormatable ndefFormat = NdefFormatable.get(detectedTag);
//If ndefFormat object is also null then it means that the tag does not support the NDEF
//and we need to break the operation.
ndef.connect();
ndef.writeNdefMessage(message);
ndef.close();
}

NFC Tag Reading
Tag detectedTag = getIntent().getParcelableExtra(NfcAdapter.EXTRA_TAG);
NdefMessage[] messages = getNdefMessages(getIntent());
NdefMessage[] getNdefMessages(Intent intent)
{
NdefMessage[] message = null;
if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(intent.getAction()))
{
Parcelable[] rawMessages =intent.getParcelableArrayExtraNfcAdapter.EXTRA_NDEF_MESSAGES);
if (rawMessages != null)
{
message = new NdefMessage[rawMessages.length];
for (int i = 0; i < rawMessages.length; i++)
{
message[i] = (NdefMessage) rawMessages[i];
}
}
else
{
Log.d("", "No messages inside tag");
}
}
else
{
Log.d("", "Unknown intent.");
finish();
}
return message;
}

Android Application Record
1) Android Application Record (AAR) is introduced in API level 14 and is a very powerful
property of Android NFC.
2) The main objective of AAR is to start the application when an NFC tag is scanned.
3) Despite the fact that the manifest file gives this property to NFC, AAR strengthens the
property because more than one application may have been registered for, and may filter, the
same intents on a mobile phone.
4) An AAR is the package name of an application. You need to insert the AAR record to an
NDEF message, similarly to the way it is done with an NDEF record.
When an NFC tag is scanned, Android searches the entire NDEF message for AAR. If it fi nds
an AAR in any of the NDEF records, it starts the corresponding application. If the application
is not installed on the device, Google Play is launched automatically to download the
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Near field communication (NFC) in android

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