NFC

o AndroidManifest.xml

<uses-sdk android:minSdkVersion="10"/>
<uses-permission android:name="android.permission.NFC"/>
<uses-feature
    android:name="android.hardware.nfc"
    android:required="true"/>

<activity android:name=".NFC.NFCActivity">
    <intent-filter>
        <action android:name="android.nfc.action.NDEF_DISCOVERED"/>
        <category android:name="android.intent.category.DEFAULT" />
        <data android:mimeType="text/plain"/>
    </intent-filter>
    <meta-data
        android:name="android.nfc.action.TECH_DISCOVERED"
        android:resource="@xml/nfc_tech_filter" />
</activity>

o  res/xml/nfc_tech_filter.xml

<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>

o  res/layout/activity_nfc.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Write a message: ">
    </TextView>

    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20sp" >

        <EditText
            android:id="@+id/edit_message"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="2"
            android:hint="message" />
        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Write" />
    </LinearLayout>

    <TextView
        android:id="@+id/nfc_contents"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        />

</LinearLayout>

o NFCActivity.java
public class NFCActivity extends AppCompatActivity {

    public static final String ERROR_DETECTED = "No NFC tag detected!";
    public static final String WRITE_SUCCESS = "Text written to the NFC tag successfully!";
    public static final String WRITE_ERROR = "Error during writing, is the NFC tag close enough to your device?";

    private static final int TYPE_TEXT = 1;
    private static final int TYPE_URI  = 2;
    private static int FILTER_TYPE;

    private NfcAdapter nfcAdapter;
    private PendingIntent pendingIntent;
    private IntentFilter writeTagFilters[];
    private boolean writeMode;
    private Tag myTag;
    private Context mContext;

    private TextView tvNFCContent;
    private TextView message;
    private Button btnWrite;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_nfc);

        mContext = this;

        tvNFCContent = (TextView) findViewById(R.id.nfc_contents);
        message = (TextView) findViewById(R.id.edit_message);
        btnWrite = (Button) findViewById(R.id.button);

        btnWrite.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v) {
                try {
                    if(myTag ==null) {
                        Toast.makeText(mContext, ERROR_DETECTED, Toast.LENGTH_LONG).show();
                    } else {
                        write(message.getText().toString(), myTag);
                        Toast.makeText(mContext, WRITE_SUCCESS, Toast.LENGTH_LONG ).show();
                    }
                } catch (IOException e) {
                    Toast.makeText(mContext, WRITE_ERROR, Toast.LENGTH_LONG ).show();
                    e.printStackTrace();
                } catch (FormatException e) {
                    Toast.makeText(mContext, WRITE_ERROR, Toast.LENGTH_LONG ).show();
                    e.printStackTrace();
                }
            }
        });

        nfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if (nfcAdapter == null) {
            // Stop here, we definitely need NFC
            Toast.makeText(this, "This device doesn't support NFC.", Toast.LENGTH_LONG).show();
            finish();
        }
        if(!nfcAdapter.isEnabled()){
            // 4.2.2 (API 17) 부터 NFC 설정 환경이 변경됨.
            if(Build.VERSION.SDK_INT > Build.VERSION_CODES.JELLY_BEAN) {
                startActivity(new Intent(android.provider.Settings.ACTION_NFC_SETTINGS));
            }else{
                startActivity(new Intent(android.provider.Settings.ACTION_WIRELESS_SETTINGS));
            }
        }

        readFromIntent(getIntent());

        pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
        IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
        tagDetected.addCategory(Intent.CATEGORY_DEFAULT);
        writeTagFilters = new IntentFilter[] { tagDetected };
    }


    /******************************************************************************
     **********************************Read From NFC Tag***************************
     ******************************************************************************/
    private void readFromIntent(Intent intent) {
        String action = intent.getAction();
        if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action)
                || NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)
                || NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
            Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
            NdefMessage[] msgs = null;
            if (rawMsgs != null) {
                msgs = new NdefMessage[rawMsgs.length];
                for (int i = 0; i < rawMsgs.length; i++) {
                    msgs[i] = (NdefMessage) rawMsgs[i];
                }
            }
            buildTagViews(msgs);
        }
    }
    private void buildTagViews(NdefMessage[] msgs) {
        if (msgs == null || msgs.length == 0) return;

        String text = "";
//        String tagId = new String(msgs[0].getRecords()[0].getType());
        byte[] payload = msgs[0].getRecords()[0].getPayload();
        String textEncoding = ((payload[0] & 128) == 0) ? "UTF-8" : "UTF-16"; // Get the Text Encoding
        int languageCodeLength = payload[0] & 0063; // Get the Language Code, e.g. "en"
        // String languageCode = new String(payload, 1, languageCodeLength, "US-ASCII");

        try {
            // Get the Text
            text = new String(payload, languageCodeLength + 1, payload.length - languageCodeLength - 1, textEncoding);
        } catch (UnsupportedEncodingException e) {
            Log.e("UnsupportedEncoding", e.toString());
        }

        tvNFCContent.setText("NFC Content: " + text);
    }


    /******************************************************************************
     **********************************Write to NFC Tag****************************
     ******************************************************************************/
    private void write(String text, Tag tag) throws IOException, FormatException {
//        NdefRecord[] records = { createTextRecord(text) };
//        NdefMessage message = new NdefMessage(records);
        NdefMessage message = createTagMessage(text, FILTER_TYPE);
        // Get an instance of Ndef for the tag.
        Ndef ndef = Ndef.get(tag);
        // Enable I/O
        ndef.connect();
        // Write the message
        ndef.writeNdefMessage(message);
        // Close the connection
        ndef.close();
    }

    private NdefMessage createTagMessage(String msg, int type){
        NdefRecord[] records = new NdefRecord[1];
        if(type == TYPE_TEXT){
            records[0] = createTextRecord(msg, Locale.KOREAN, true);
        }else if(type == TYPE_URI){
            records[0] = createUriRecord(msg.getBytes());
        }

        NdefMessage message = new NdefMessage(records);
        return message;
    }

    private NdefRecord createTextRecord(String text) throws UnsupportedEncodingException {
        String lang       = "en";
        byte[] textBytes  = text.getBytes();
        byte[] langBytes  = lang.getBytes("US-ASCII");
        int    langLength = langBytes.length;
        int    textLength = textBytes.length;
        byte[] payload    = new byte[1 + langLength + textLength];

        // set status byte (see NDEF spec for actual bits)
        payload[0] = (byte) langLength;

        // copy langbytes and textbytes into payload
        System.arraycopy(langBytes, 0, payload, 1,              langLength);
        System.arraycopy(textBytes, 0, payload, 1 + langLength, textLength);

        NdefRecord recordNFC = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,  NdefRecord.RTD_TEXT,  new byte[0], payload);

        return recordNFC;
    }

    /**
     * https://developer.android.com/guide/topics/connectivity/nfc/nfc#java
     * @param payload
     * @param locale
     * @param encodeInUtf8
     * @return
     */
    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 << 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;
    }

    private NdefRecord createUriRecord(byte[] data){
        return new NdefRecord(NdefRecord.TNF_ABSOLUTE_URI, NdefRecord.RTD_URI, new byte[0], data);
    }


    /**
     * 단말이 NFC 태그를 수신하면 NDEF메시지인지 확인하여 NDEF메시지이면 NDEF_DISCOVERED를 액션으로 가진
     * Activity중 처리할 Activity를 찾아 인텐트를 전달한다.
     * 만약 아니면 TECH_DISCOVERED를 가진 Activit에게 전달한다.
     * 그것도 없으면 TAG_DISCOVERED를 가진 Activity를 구동한다.
     * @param intent
     */
    @Override
    protected void onNewIntent(Intent intent) {
        setIntent(intent);
        readFromIntent(intent);
        if(NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())){
            myTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
        }

        if("text/plain".equals(intent.getType()))
            FILTER_TYPE = 1;
        else
            FILTER_TYPE = 2;
    }

    @Override
    public void onPause(){
        super.onPause();
        WriteModeOff();
    }

    @Override
    public void onResume(){
        super.onResume();
        WriteModeOn();
    }

    /******************************************************************************
     **********************************Enable Write********************************
     ******************************************************************************/
    private void WriteModeOn(){
        writeMode = true;
        nfcAdapter.enableForegroundDispatch(this, pendingIntent, writeTagFilters, null);
    }

    /******************************************************************************
     **********************************Disable Write*******************************
     ******************************************************************************/
    private void WriteModeOff(){
        writeMode = false;
        nfcAdapter.disableForegroundDispatch(this);
    }
}

https://developer.android.com/guide/topics/connectivity/nfc/nfc

https://www.codexpedia.com/android/android-nfc-read-and-write-example/

http://blog.naver.com/PostView.nhn?blogId=horajjan&logNo=220492560615

http://humble.tistory.com/34