Android中NFC功能流程图解析及代码演示『轉』

在Android4.0推出的时候，一个非常引人注目的功能就是NFC(Near Field Communication).

Near Field Communication (NFC) is a set of short-range wireless technologies, typically requiring a distance of 4cm or less to initiate a connection. NFC allows you to share small payloads of data between an NFC tag and an Android-powered device, or between two Android-powered devices.

翻译：
近场通讯(NFC)是一系列短距离无线技术，一般需要4cm或者更短去初始化连接。近场通讯(NFC)允许你在NFC tag和Android设备或者两个Android设备间共享小负载数据。

典型的应用为刷卡应用，如刷信用卡，公交车卡，吃饭的饭卡之类。腾讯2011年1月份文章“Android首款NFC近场通信应用推出”，说明了基于Android的NFC应用目前已经有了，得益于日本在手机刷卡的应用氛围。据2011年7月网易文章“PayPal推出Android系统NFC移动支付服务”报道，PayPal已经做了尝试了，相信这股风很快要刮到中国。

下面我们从技术的层面来分析一下这个技术。

官方的图片示例为：

这是NFC的开发流程，参考文章 “【NFC在android中的应用API】”。

相关的类代码有：NfcAdapter,NdefMessage, NdefRecord,ACTION_TAG_DISCOVERED.
在功能层面上，涉及到了NFC的读写功能。下面我们分别来做总结。
在代码层上面：

使用的时候，需要在AndroidManifest.xml里面加一些权限以及属性。

           "android.permission.NFC"            />                                          "android.hardware.nfc"            android:required=           "true"            />                                          "10"           />

这里注意，在Android Version 9的时候仅仅支持了ACTION_TAG_DISCOVERED，对于其他的需要10以上。

在上面的基础上，还需要增加intent-filter的支持。

           "android.nfc.action.NDEF_DISCOVERED"           />                                                         "android.intent.category.DEFAULT"           />                                                         "text/plain"            />

获取NfcAdapter的代码为：

public static String getStatusNfcDevice () { NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(); if (nfcAdapter.isEnabled()) { String status = "enabled" ; return status; } else { String status = "disabled" ; return status; } }

处理函数为

public void onResume() { super .onResume(); if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) { Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES); if (rawMsgs != null ) { msgs = new NdefMessage[rawMsgs.length]; for ( int i = 0 ; i < rawMsgs.length; i++) { msgs[i] = (NdefMessage) rawMsgs[i]; } } } //process the msgs array }

完整的一个操作代码摘自Google Android NFC Guide代码（略加注释）：

package com.example.android.beam; import android.app.Activity; import android.content.Intent; import android.nfc.NdefMessage; import android.nfc.NdefRecord; import android.nfc.NfcAdapter; import android.nfc.NfcAdapter.CreateNdefMessageCallback; import android.nfc.NfcEvent; import android.os.Bundle; import android.os.Parcelable; import android.widget.TextView; import android.widget.Toast; import java.nio.charset.Charset; //继承并实现接口CreateNdefMessageCallback方法createNdefMessage public class Beam extends Activity implements CreateNdefMessageCallback { NfcAdapter mNfcAdapter; TextView textView; @Override public void onCreate(Bundle savedInstanceState) { super .onCreate(savedInstanceState); setContentView(R.layout.main); TextView textView = (TextView) findViewById(R.id.textView); // Check for available NFC Adapter //检测是否有NFC适配器 mNfcAdapter = NfcAdapter.getDefaultAdapter( this ); if (mNfcAdapter == null ) { Toast.makeText( this , "NFC is not available" , Toast.LENGTH_LONG).show(); finish(); return ; } // Register callback //注册回调函数 mNfcAdapter.setNdefPushMessageCallback( this , this ); } @Override public NdefMessage createNdefMessage(NfcEvent event) { String text = ( "Beam me up, Android!\n\n" + "Beam Time: " + System.currentTimeMillis()); //回调函数，构造NdefMessage格式 NdefMessage msg = new NdefMessage( new NdefRecord[] { createMimeRecord( "application/com.example.android.beam" , text.getBytes()) /** * The Android Application Record (AAR) is commented out. When a device * receives a push with an AAR in it, the application specified in the AAR * is guaranteed to run. The AAR overrides the tag dispatch system. * You can add it back in to guarantee that this * activity starts when receiving a beamed message. For now, this code * uses the tag dispatch system. */ //,NdefRecord.createApplicationRecord("com.example.android.beam") }); return msg; } @Override public void onResume() { super .onResume(); // Check to see that the Activity started due to an Android Beam //得到是否检测到ACTION_NDEF_DISCOVERED触发 if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) { processIntent(getIntent()); } } //重载Activity类方法处理当新Intent到来事件 @Override public void onNewIntent(Intent intent) { // onResume gets called after this to handle the intent setIntent(intent); } /** * Parses the NDEF Message from the intent and prints to the TextView */ //关键处理函数，处理扫描到的NdefMessage void processIntent(Intent intent) { textView = (TextView) findViewById(R.id.textView); Parcelable[] rawMsgs = intent.getParcelableArrayExtra( NfcAdapter.EXTRA_NDEF_MESSAGES); // only one message sent during the beam NdefMessage msg = (NdefMessage) rawMsgs[ 0 ]; // record 0 contains the MIME type, record 1 is the AAR, if present textView.setText( new String(msg.getRecords()[ 0 ].getPayload())); } /** * Creates a custom MIME type encapsulated in an NDEF record */ public NdefRecord createMimeRecord(String mimeType, byte [] payload) { byte [] mimeBytes = mimeType.getBytes(Charset.forName( "US-ASCII" )); NdefRecord mimeRecord = new NdefRecord( NdefRecord.TNF_MIME_MEDIA, mimeBytes, new byte [ 0 ], payload); return mimeRecord; } }

上面代码还需要在AndroidManifest.xml文件里面添加

           "android.nfc.action.NDEF_DISCOVERED"           />                                                       "android.intent.category.DEFAULT"           />                                                       "application/com.example.android.beam"           />

在对NFC设备进行写操作的时候，相关代码：

private void enableTagWriteMode() { mWriteMode = true ; IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED); mWriteTagFilters = new IntentFilter[] { tagDetected }; mNfcAdapter.enableForegroundDispatch( this , mNfcPendingIntent, mWriteTagFilters, null ); }

@Override protected void onNewIntent(Intent intent) { // Tag writing mode if (mWriteMode && NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())) { Tag detectedTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG); if (NfcUtils.writeTag(NfcUtils.getPlaceidAsNdef(placeidToWrite), detectedTag)) { Toast.makeText( this , "Success: Wrote placeid to nfc tag" , Toast.LENGTH_LONG) .show(); NfcUtils.soundNotify( this ); } else { Toast.makeText( this , "Write failed" , Toast.LENGTH_LONG).show(); } } }

/* * Writes an NdefMessage to a NFC tag */ public static boolean writeTag(NdefMessage message, Tag tag) { int size = message.toByteArray().length; try { Ndef ndef = Ndef.get(tag); if (ndef != null ) { ndef.connect(); if (!ndef.isWritable()) { return false ; } if (ndef.getMaxSize() < size) { return false ; } ndef.writeNdefMessage(message); return true ; } else { NdefFormatable format = NdefFormatable.get(tag); if (format != null ) { try { format.connect(); format.format(message); return true ; } catch (IOException e) { return false ; } } else { return false ; } } } catch (Exception e) { return false ; } }

相关的AndroidManifest.xml文件配置如下：

           ".CheckInActivity"           >                                                                                                         "android.nfc.action.NDEF_DISCOVERED"           />                                                           "application/vnd.facebook.places"           />                                                           "android.intent.category.DEFAULT"           />

参考文章：

http://developer.android.com/guide/topics/nfc/nfc.html

http://stackoverflow.com/questions/5078649/android-nfc-sample-demo-reads-only-fake-information-from-the-tag

http://developer.android.com/guide/topics/nfc/index.html

http://money.163.com/11/0714/09/78TPVJOL00253CVK.html

http://www.cnblogs.com/jfttcjl/archive/2011/11/09/2242045.html

http://www.jessechen.net/blog/how-to-nfc-on-the-android-platform/

另外有几个专门推动NFC技术的联盟：

http://open-nfc.org/wp/nfchal/

http://www.classic.nxp.com/theme/nfc/

http://www.nfc-forum.org/home/

官方关于NFC的翻译文档见：

http://blog.csdn.net/nicebooks/article/details/6223956

参考库：

http://code.google.com/p/guava-libraries/

在对NFC设备进行写操作的时候，相关代码：

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