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, , new Intent(this,getClass()), );

         //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 = ;
         char status = (char) (utfBit + langBytes.length);
         //申请空间
         byte[] data = new byte[ + langBytes.length + textBytes.length];
         //第1字节是状态码
         data[] = (byte) status;
         System.arraycopy(langBytes, , data, , langBytes.length);
         System.arraycopy(textBytes, , data,  + langBytes.length,textBytes.length);
         NdefRecord record = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,NdefRecord.RTD_TEXT, new byte[], data);

         return record;
     }

     void processIntent(Intent intent) {

         Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);

         NdefMessage msg = (NdefMessage) rawMsgs[];
         String text = TextRecord.parse(msg.getRecords()[]).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[] & 0x80) == ) ? "UTF-8"
                     : "UTF-16";
             int languageCodeLength = payload[] & 0x3f;
             String languageCode = new String(payload, , languageCodeLength,"US-ASCII");
             String text = new String(payload, languageCodeLength + ,
                     payload.length - languageCodeLength - , textEncoding);
             return new TextRecord(text);
         } catch (UnsupportedEncodingException e) {
             // should never happen unless we get a malformed tag.
             throw new IllegalArgumentException(e);
         }
     }
 }