NFC(12)使用Android Beam技术传输文本数据及它是什么

Android Beam技术是什么

　　Android Beam的基本理念就是两部（只能是1对1,不可像蓝牙那样1对多）NFC设备靠近时（一般是背靠背），通过触摸一部NFC设备的屏幕，将数据推向另外一部NFC设备。在传递数据的过程中，两部NFC设备不能离得太远，否则NFC连接将中断。

使用Android Beam技术传输文本数据

　　目前2015-09-05在android支持的nfc设备上,只要我们提供数据类型就可,不用手动像socket那样手动write(data),由系统完成,

Android SDK提供了如下两个用于传递消息的方法

　　NfcAdapter.setNdefPushMessage

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

　　NfcAdapter.setNdefPushMessageCallback ,这是一个回调,直到需要传输数据时才准备数据.

public void setNdefPushMessageCallback(CreateNdefMessageCallback callback, Activity activity, Activity ... activities);
public NdefMessage createNdefMessage(NfcEvent event)

使用Android Beam技术传输文本示例

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;
/*
 * 两个nfc设备通信示例
 * 本例中使用第2种方法传递数据,NfcAdapter.setNdefPushMessageCallback
 */
public class AndroidBeamMainActivity extends Activity 
        implements CreateNdefMessageCallback //传输数据的方法
        , OnNdefPushCompleteCallback {//OnNdefPushCompleteCallback是传输完毕的事件回调

    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);
        
        //设置当前aty为处理nfc的应用,注意aty为singleTop
        mNfcAdapter = mNfcAdapter.getDefaultAdapter(this);
        mPendingIntent = PendingIntent.getActivity(this, 0, new Intent(this,getClass()), 0);

        //数据传输函数回调
        mNfcAdapter.setNdefPushMessageCallback(this, this);
        //传输完毕回调
        mNfcAdapter.setOnNdefPushCompleteCallback(this, this);

    }
    /*
     * from OnNdefPushCompleteCallback
     * 数据传输完毕的回调.
     */
    @Override
    public void onNdefPushComplete(NfcEvent event) {
        Log.d("message", "complete");
    }

    /*
     * 这是CreateNdefMessageCallback的回调,
     * 创建一个NdefMessage.这里是把EditText中内容封装成NdefMessage
     * NdefMessage中record的类型可以自己随意,如text,uri,application
     * 
     */
    @Override
    public NdefMessage createNdefMessage(NfcEvent event) {
        String text = mBeamText.getText().toString().trim();
        if ("".equals(text))
            text = "默认文本";
        
        /*
         * 创建一个ApplicationRecord类型的record
         * 启动计算器.
         */
        /*NdefMessage ndefMessage = new NdefMessage(
                new NdefRecord[] { NdefRecord.createApplicationRecord("com.android.calculator2") });*/
        
        /*
         * 根据txt创建一个NdefRecord,并把它放入到NdefMessage中.
         */
        NdefMessage ndefMessage = new NdefMessage(new NdefRecord[]{createTextRecord(text)});
        
        return ndefMessage;
    }

    /*
     *注册当前aty为nfc处理功能
     */
    @Override
    public void onResume() {
        super.onResume();
        if (mNfcAdapter != null)
            mNfcAdapter.enableForegroundDispatch(this, mPendingIntent, null,
                    null);

    }
    /*
     *注销当前aty处理nfc的功能 
     */
    @Override
    public void onPause() {
        super.onPause();
        if (mNfcAdapter != null)
            mNfcAdapter.disableForegroundDispatch(this);
    }

    @Override
    public void onNewIntent(Intent intent) {
        /*
         * 当本aty启动时,有另个nfc设备通过beam与本机配对并传来数据时,
         * 本函数接收数据,并用toast提示出来.
         * 如果要aty未启动,那么系统调用默认的处理程序.
         */
        processIntent(intent);
    }

    /*
     * 根据文本创建一个NdefRecord,
     * 注意ndef文本格式规范
     * 1,这些数据的第1个字节描述了数据的状态，
　　  * 2,然后若干个字节描述文本的语言编码，
　　  * 3,最后剩余字节表示文本数据。
     */
    public NdefRecord createTextRecord(String text) {
        //语言编码
        byte[] langBytes = Locale.CHINA.getLanguage().getBytes(Charset.forName("US-ASCII"));
        
        //设置text的字符编码为utf8
        Charset utfEncoding = Charset.forName("UTF-8");
        byte[] textBytes = text.getBytes(utfEncoding);
        int utfBit = 0;
        char status = (char) (utfBit + langBytes.length);
        //申请空间
        byte[] data = new byte[1 + langBytes.length + textBytes.length];
        //第1字节是状态码
        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();
    }
}

 

解析文本的类

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;
    }

    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);
        }
    }
}