14、NFC技術：使用Android Beam技術傳輸文本

Android Beam的基本理念

     Android Beam的基本理念就是兩部（只能是兩部）NFC設備靠近時（一般是背靠背），通過觸摸一部NFC設備的屏幕，將數據推向另外一部NFC設備。在傳遞數據的過程中，兩部NFC設備不能離得太遠，否則NFC連接將中斷。

Android Beam API

Android SDK提供了如下兩個用於傳遞消息的方法。

NfcAdapter.setNdefPushMessage

NfcAdapter.setNdefPushMessageCallback

public void setNdefPushMessage(NdefMessage message, Activity activity, Activity ... activities);

public void setNdefPushMessageCallback(CreateNdefMessageCallback callback, Activity activity, Activity ... activities);

public NdefMessage createNdefMessage(NfcEvent event)

Demo

           

import java.nio.charset.Charset;
import java.util.Locale;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.Intent;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.NfcAdapter.CreateNdefMessageCallback;
import android.nfc.NfcAdapter.OnNdefPushCompleteCallback;
import android.nfc.NfcEvent;
import android.os.Bundle;
import android.os.Parcelable;
import android.util.Log;
import android.widget.EditText;
import android.widget.Toast;

/**
 * 兩部android手機，進行傳入文本信息。
 * @author dr
 *
 */
public class AndroidBeamMainActivity extends Activity implements
        CreateNdefMessageCallback, OnNdefPushCompleteCallback {

    private EditText mBeamText;

    private NfcAdapter mNfcAdapter;
    private PendingIntent mPendingIntent;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_android_beam);
        mBeamText = (EditText) findViewById(R.id.edittext_beam_text);
        
        mNfcAdapter = mNfcAdapter.getDefaultAdapter(this);
        mPendingIntent = PendingIntent.getActivity(this, 0, new Intent(this,
                getClass()), 0);

        mNfcAdapter.setNdefPushMessageCallback(this, this);
        mNfcAdapter.setOnNdefPushCompleteCallback(this, this);
    }

    @Override    /** 窗口處理完成 */
    public void onNdefPushComplete(NfcEvent event) {
        Log.d("message", "complete");
    }

    @Override  /** 如果另外一台手機，靠近當前這部手機 */
    public NdefMessage createNdefMessage(NfcEvent event) {
        String text = mBeamText.getText().toString().trim();
        if ("".equals(text))
            text = "默認文本";
        /*
         *  "com.android.calculator2"  官方原生計算器包。
         *  當另外一部手機靠近這部手機時，會啟動計算器。
         *  
         * NdefMessage ndefMessage = new NdefMessage( new NdefRecord[] {
         * NdefRecord .createApplicationRecord("com.android.calculator2") });
         */
        NdefMessage ndefMessage = new NdefMessage(
                new NdefRecord[] { createTextRecord(text) });

        return ndefMessage;
    }

    @Override
    public void onResume() {
        super.onResume();
        if (mNfcAdapter != null)
            mNfcAdapter.enableForegroundDispatch(this, mPendingIntent, null,
                    null);
    }

    @Override
    public void onPause() {
        super.onPause();
        if (mNfcAdapter != null)
            mNfcAdapter.disableForegroundDispatch(this);
    }

    @Override
    public void onNewIntent(Intent intent) {
        // 用於顯示接收手機的信息。如果接收手機沒有打開，會默認調用系統的黑界面。
        processIntent(intent);
    }

    /** 根據文本創建 NdefRecord 這個對象 */
    public NdefRecord createTextRecord(String text) {
        byte[] langBytes = Locale.CHINA.getLanguage().getBytes(
                Charset.forName("US-ASCII"));
        Charset utfEncoding = Charset.forName("UTF-8");
        byte[] textBytes = text.getBytes(utfEncoding);
        int utfBit = 0;
        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;
    }

    void processIntent(Intent intent) {
        Parcelable[] rawMsgs = intent
                .getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);

        NdefMessage msg = (NdefMessage) rawMsgs[0];
        String text = TextRecord.parse(msg.getRecords()[0]).getText();
        Toast.makeText(this, text, Toast.LENGTH_LONG).show();
    }
}

import java.io.UnsupportedEncodingException;
import java.util.Arrays;
import android.nfc.NdefRecord;

public class TextRecord {
    private final String mText;

    private TextRecord(String text) {
        mText = text;
    }

    public String getText() {
        return mText;
    }

    // 將純文本內容從NdefRecord對象中解析出來
    public static TextRecord parse(NdefRecord record) {

        if (record.getTnf() != NdefRecord.TNF_WELL_KNOWN)
            return null;
        if (!Arrays.equals(record.getType(), NdefRecord.RTD_TEXT))
            return null;

        try {
            byte[] payload = record.getPayload();
            /*
             * payload[0] contains the "Status Byte Encodings" field, per the
             * NFC Forum "Text Record Type Definition" section 3.2.1.
             * 
             * bit7 is the Text Encoding Field.
             * 
             * if (Bit_7 == 0): The text is encoded in UTF-8 if (Bit_7 == 1):
             * The text is encoded in UTF16
             * 
             * Bit_6 is reserved for future use and must be set to zero.
             * 
             * Bits 5 to 0 are the length of the IANA language code.
             */
            String textEncoding = ((payload[0] & 0x80) == 0) ? "UTF-8"
                    : "UTF-16";
            int languageCodeLength = payload[0] & 0x3f;
            String languageCode = new String(payload, 1, languageCodeLength,
                    "US-ASCII");
            String text = new String(payload, languageCodeLength + 1,
                    payload.length - languageCodeLength - 1, textEncoding);
            return new TextRecord(text);
        } catch (UnsupportedEncodingException e) {
            // should never happen unless we get a malformed tag.
            throw new IllegalArgumentException(e);
        }
    }

}

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

    <EditText
        android:id="@+id/edittext_beam_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="請輸入要傳輸的文本"/>

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="5dp"
        android:text="請將當前設備靠近其他NFC設備，別忘了觸摸屏幕哦！"
        android:textSize="16sp" />

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="10dp"
        android:src="@drawable/read_nfc_tag" />

</LinearLayout>