Android中NFC功能流程图解析及代码演示

Android中NFC功能流程图解析及代码演示在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。

<uses-permissionandroid:name="android.permission.NFC"/><uses-feature android:name="android.hardware.nfc"android:required="true"/><uses-sdk android:minSdkVersion="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。

<intent-filter><actionandroid:name="android.nfc.action.NDEF_DISCOVERED"/><categoryandroid:name="android.intent.category.DEFAULT"/><data android:mimeType="text/plain"/></intent-filter>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_M ESSAGES);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;importandroid.nfc.NfcAdapter.CreateNdefMessageCallback; import android.nfc.NfcEvent;import android.os.Bundle;import android.os.Parcelable;import android.widget.TextView;importimport java.nio.charset.Charset;//继承并实现接口CreateNdefMessageCallback方法createNdefMessagepublic class Beam extends Activity implements CreateNdefMessageCallback {NfcAdapter mNfcAdapter;TextView textView;@Overridepublic void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);setContentView(yout.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);}@Overridepublic 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())//,NdefRecord.createApplicationRecord("com.example.and roid.beam")});return msg;}@Overridepublic 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@Overridepublic void onNewIntent(Intent intent) {// onResume gets called after this to handle the intent setIntent(intent);}//关键处理函数，处理扫描到的NdefMessagevoid processIntent(Intent intent) {textView = (TextView) findViewById(R.id.textView);Parcelable[] rawMsgs = intent.getParcelableArrayExtra( NfcAdapter.EXTRA_NDEF_MESSAGES);// only one message sent during the beamNdefMessage msg = (NdefMessage) rawMsgs[0];// record 0 contains the MIME type, record 1 is the AAR, if presenttextView.setText(newString(msg.getRecords()[0].getPayload()));}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<intent-filter><actionandroid:name="android.nfc.action.NDEF_DISCOVERED"/><categoryandroid:name="android.intent.category.DEFAULT"/><dataandroid:mimeType="application/com.example.android.beam "/></intent-filter>在对NFC设备进行写操作的时候，相关代码：private void enableTagWriteMode() {mWriteMode = true;IntentFilter tagDetected = newIntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);mWriteTagFilters = new IntentFilter[] { tagDetected };mNfcAdapter.enableForegroundDispatch(this,mNfcPendingIntent, mWriteTagFilters, null);}@Overrideprotected void onNewIntent(Intent intent) {// Tag writing modeif (mWriteMode &&NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getActi on())) {Tag detectedTag =intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);if(NfcUtils.writeTag(NfcUtils.getPlaceidAsNdef(placeidTo Write), 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();}}}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：<activity android:name=".CheckInActivity"><intent-filter><actionandroid:name="android.nfc.action.NDEF_DISCOVERED"/><dataandroid:mimeType="application/vnd.facebook.places"/><categoryandroid:name="android.intent.category.DEFAULT"/></intent-filter></activity>参考文章：参考文章：/guide/topics/nfc/nfc.html/questions/5078649/android-nfc-sample-demo-reads-only-fake-inform ation-from-the-tag/guide/topics/nfc/index.html/11/0714/09/78TPVJOL00253CVK.html/jfttcjl/archive/2011/11/09/2242045.html/blog/how-to-nfc-on-the-android-platform/另外有几个专门推动NFC技术的联盟：/wp/nfchal//theme/nfc//home/官方关于NFC的翻译文档见：/nicebooks/article/details/6223956参考库：/p/guava-libraries/。