14、NFC技术：使用Android Beam技术传输文本

Android Beam的基本理念

Android Beam的基本理念就是两部（只能是两部）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。

Android Beam API

Android SDK提供了如下两个用于传递消息的方法。

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;

 /**
  * 两部android手机，进行传入文本信息。
  * @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    /** 窗口处理完成 */
     public void onNdefPushComplete(NfcEvent event) {
         Log.d("message", "complete");
     }

     @Override  /** 如果另外一台手机，靠近当前这部手机 */
     public NdefMessage createNdefMessage(NfcEvent event) {
         String text = mBeamText.getText().toString().trim();
         if ("".equals(text))
             text = "默认文本";
         /*
          *  "com.android.calculator2"  官方原生计算器包。
          *  当另外一部手机靠近这部手机时，会启动计算器。
          *
          * 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) {
         // 用于显示接收手机的信息。如果接收手机没有打开，会默认调用系统的黑界面。
         processIntent(intent);
     }

     /** 根据文本创建 NdefRecord 这个对象 */
     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;
     }

     // 将纯文本内容从NdefRecord对象中解析出来
     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="请输入要传输的文本"/>

     <TextView
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_marginBottom="5dp"
         android:text="请将当前设备靠近其他NFC设备，别忘了触摸屏幕哦！"
         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>