學習開源項目NFCard，最新版源碼以及幾年前代碼相比較，發現之前的版本可以支持讀羊城通，而現在不再支持讀羊城通卡信息，那定一個小目標。通過NFC讀取羊城通卡片信息之余額和交易記錄。

實現的效果如圖：

目錄
1.建立工程，編寫NFC相關代碼；
2.根據開源項目中的指令，讀取余額；
3.根據開源項目中的指令，讀取交易記錄；
4.根據卡片原始信息解析數據；

一、編寫NFC相關代碼

import android.app.PendingIntent;import android.content.Intent;import android.nfc.NfcAdapter;import android.nfc.Tag;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;public class MainActivity extends AppCompatActivity {private NfcAdapter mNfcAdapter;private PendingIntent mPendingIntent;private Intent mIntent;private final int READER_FLAGS = NfcAdapter.FLAG_READER_NFC_A | NfcAdapter.FLAG_READER_SKIP_NDEF_CHECK;private NfcAdapter.ReaderCallback mReaderCallback = new NfcAdapter.ReaderCallback() {@Overridepublic void onTagDiscovered(Tag tag) {System.out.println(tag.toString());}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);}@Overrideprotected void onStart() {super.onStart();initNfc();}@Overrideprotected void onResume() {super.onResume();registerNfc();}@Overrideprotected void onPause() {super.onPause();unRegisterNfc();}private void initNfc() {mNfcAdapter = NfcAdapter.getDefaultAdapter(this);mIntent = new Intent(NfcAdapter.ACTION_TECH_DISCOVERED);mIntent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);mPendingIntent = PendingIntent.getActivity(this, 0, mIntent, 0);}private void registerNfc() {Bundle bundle = new Bundle();mNfcAdapter.enableReaderMode(this, mReaderCallback, READER_FLAGS, bundle);}private void unRegisterNfc() {mNfcAdapter.disableReaderMode(this);}}

運行上述代碼的效果：(羊城通緊貼在手機NFC感應處)

I/System.out: TAG: Tech [android.nfc.tech.IsoDep, android.nfc.tech.NfcA]

看源碼解釋一下：
注冊NFC調用了NfcAdapter的enableReaderMode方法，先看看源碼：

/*** Limit the NFC controller to reader mode while this Activity is in the foreground.** <p>In this mode the NFC controller will only act as an NFC tag reader/writer,* thus disabling any peer-to-peer (Android Beam) and card-emulation modes of* the NFC adapter on this device.** <p>Use {@link #FLAG_READER_SKIP_NDEF_CHECK} to prevent the platform from* performing any NDEF checks in reader mode. Note that this will prevent the* {@link Ndef} tag technology from being enumerated on the tag, and that* NDEF-based tag dispatch will not be functional.** <p>For interacting with tags that are emulated on another Android device* using Android's host-based card-emulation, the recommended flags are* {@link #FLAG_READER_NFC_A} and {@link #FLAG_READER_SKIP_NDEF_CHECK}.** @param activity the Activity that requests the adapter to be in reader mode* @param callback the callback to be called when a tag is discovered* @param flags Flags indicating poll technologies and other optional parameters* @param extras Additional extras for configuring reader mode.*/public void enableReaderMode(Activity activity, ReaderCallback callback, int flags,Bundle extras) {mNfcActivityManager.enableReaderMode(activity, callback, flags, extras);}

三行代碼三大段注釋，nice。enableReaderMode()摳腳翻譯如下：

限制NFC的模式為讀卡器模式

在這種模式中，就僅僅是可以用NFC讀寫帶有NFC芯片的標簽（卡片、貼紙等)，不允許點對點模式和卡模擬模式。

可以通過FLAG_READER_SKIP_NDEF_CHECK這個標志過濾NDEF標簽，這個就是標志就是第三個參數啦，NDEF（NFC Data Exchange Format，NFC數據交換格式）是Android SDK API主要支持NFC論壇標準。

如果是準備與另一臺Android卡模擬設備交互，那么建議設置的標志就是FLAG_READER_NFC_A和FLAG_READER_SKIP_NDEF_CHECK

參數callback：發現符合的標簽就回調到callback
參數extras ： 對讀卡器模式進行一些配置（先晾它一會，目前只是傳了一個空bundle進去）
參數flags：標志

上述參數中有一個flags，我們順便也看看有哪些flag以及flag的作用是什么，看源碼然后摳腳解釋下：

/*** Flag for use with {@link #enableReaderMode(Activity, ReaderCallback, int, Bundle)}.* <p>* Setting this flag enables polling for Nfc-A technology.*/public static final int FLAG_READER_NFC_A = 0x1;/*** Flag for use with {@link #enableReaderMode(Activity, ReaderCallback, int, Bundle)}.* <p>* Setting this flag enables polling for Nfc-B technology.*/public static final int FLAG_READER_NFC_B = 0x2;/*** Flag for use with {@link #enableReaderMode(Activity, ReaderCallback, int, Bundle)}.* <p>* Setting this flag enables polling for Nfc-F technology.*/public static final int FLAG_READER_NFC_F = 0x4;/*** Flag for use with {@link #enableReaderMode(Activity, ReaderCallback, int, Bundle)}.* <p>* Setting this flag enables polling for Nfc-V (ISO15693) technology.*/public static final int FLAG_READER_NFC_V = 0x8;/*** Flag for use with {@link #enableReaderMode(Activity, ReaderCallback, int, Bundle)}.* <p>* Setting this flag enables polling for NfcBarcode technology.*/public static final int FLAG_READER_NFC_BARCODE = 0x10;/*** Flag for use with {@link #enableReaderMode(Activity, ReaderCallback, int, Bundle)}.* <p>* Setting this flag allows the caller to prevent the* platform from performing an NDEF check on the tags it* finds.*/public static final int FLAG_READER_SKIP_NDEF_CHECK = 0x80;/*** Flag for use with {@link #enableReaderMode(Activity, ReaderCallback, int, Bundle)}.* <p>* Setting this flag allows the caller to prevent the* platform from playing sounds when it discovers a tag.*/public static final int FLAG_READER_NO_PLATFORM_SOUNDS = 0x100; flagvaluemeaning

FLAG_READER_NFC_A	0x1	支持NFCA數據格式
FLAG_READER_NFC_B	0x2	支持NFCB數據格式
FLAG_READER_NFC_F	0x4	支持NFCF數據格式
FLAG_READER_NFC_V	0x8	支持NFCV數據格式
FLAG_READER_NFC_BARCODE	0x10	支持NFCBARCODE數據格式
FLAG_READER_SKIP_NDEF_CHECK	0x80	過濾NDEF數據格式
FLAG_READER_NO_PLATFORM_SOUNDS	0x100	關閉發現TAG時的聲音

看完上述，估計有點蒙，好像也有點跑偏，趕緊回到注冊NFC的這個方法中，我們在onResume中調用了enableReaderMode，此方法在卡片(此處指羊城通)貼到手機NFC感應處時會回調到ReaderCallback中，所以我們在onTagDiscovered這個回調中即可與卡片進行交互。

二、根據指令讀取羊城通余額

首先我們可以去交通信息中心下載一份《城市公共交通IC卡技術規范》卡片的部分，認真去閱讀（一頭扎進去估計難看懂），我們知道選擇目錄的指令為：00A40400+lc+文件名+00；讀取余額的指令為：805C000204（指令為7816報文格式）
其次我們可以去閱讀NFCard這個開源項目，從源碼中知道，選擇的文件名為：”PAY.TICL”，lc為：08
到此，我們整理下所需指令：

commandmeaning

00A40400085041592E5449434C00	選擇PAY.TICL目錄(P的十六進制ASCII碼為50)
805C000204	讀取余額

上述拼接指令過程中，需要把字符換成對應的十六進制ASCII碼，好在Google的Sample給我們提供了這些轉換方法，恩，又可以抄一波(具體Sample路徑：”sdk根目錄”\samples\android-“version”\connectivity\CardReader..\LoyaltyCardReader.java):

/*** Utility class to convert a byte array to a hexadecimal string.** @param bytes Bytes to convert* @return String, containing hexadecimal representation.*/public static String ByteArrayToHexString(byte[] bytes) {final char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};char[] hexChars = new char[bytes.length * 2];int v;for ( int j = 0; j < bytes.length; j++ ) {v = bytes[j] & 0xFF;hexChars[j * 2] = hexArray[v >>> 4];hexChars[j * 2 + 1] = hexArray[v & 0x0F];}return new String(hexChars);}/*** Utility class to convert a hexadecimal string to a byte string.** <p>Behavior with input strings containing non-hexadecimal characters is undefined.** @param s String containing hexadecimal characters to convert* @return Byte array generated from input*/public static byte[] HexStringToByteArray(String s) {int len = s.length();byte[] data = new byte[len / 2];for (int i = 0; i < len; i += 2) {data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)+ Character.digit(s.charAt(i+1), 16));}return data;}

有了卡片，有了卡片指令，我們就開始通過NFC進行交互
回到我們NFC的回調方法中，我們可以從回調方法onTagDiscovered(Tag tag)拿到一個TAG，這個TAG從輸出的日志看，有IsoDep，通過IsoDep類的transceive方法即可發送指令數據到卡片并且返回響應數據：

@Overridepublic void onTagDiscovered(Tag tag) {System.out.println(tag.toString());if (tag.toString().contains(IsoDep.class.getName())) {IsoDep isoDep = IsoDep.get(tag);if (isoDep != null) {try {isoDep.connect();//連接//選擇目錄System.out.print("指令報文:" + "00A40400085041592E5449434C00");byte[] resp_dir = isoDep.transceive(Commands.HexStringToByteArray("00A40400085041592E5449434C00"));System.out.println(" 響應報文:" + Commands.ByteArrayToHexString(resp_dir));//讀取余額System.out.print("指令報文:" + "805C000204");byte[] resp_balance = isoDep.transceive(Commands.HexStringToByteArray("805C000204"));System.out.println(" 響應報文:" + Commands.ByteArrayToHexString(resp_balance));} catch (IOException e) {e.printStackTrace();}}}}

具體數據為：

I/System.out: 指令報文:00A40400085041592E5449434C00 響應報文:6F3484085041592E5449434CA5289F0801029F0C21FFFFFFFFFFFFFFFF000000000000000000000000000000002016122400000186A09000 I/System.out: 指令報文:805C000204 響應報文:00000E479000

根據7816報文格式，響應報文格式為DATA+SW1+SW2，SW1和SW2為狀態字，分別占一個字節，由此DATA=00000E47，SW1=90，SW2=00。00000E47轉十進制則是3655，這個時候我們用QQ來讀一下羊城通對比一下余額是否正確，QQ讀出余額如下圖：

我們使用的transceive方法，將原始數據發送至卡片標簽，并且得到響應，如果中途移開卡片，則會拋出TagLostException(也是繼承IOException)，如果中途讀寫失敗或者取消，則拋出IOException。

/*** Send raw ISO-DEP data to the tag and receive the response.** <p>Applications must only send the INF payload, and not the start of frame and* end of frame indicators. Applications do not need to fragment the payload, it* will be automatically fragmented and defragmented by {@link #transceive} if* it exceeds FSD/FSC limits.** <p>Use {@link #getMaxTransceiveLength} to retrieve the maximum number of bytes* that can be sent with {@link #transceive}.** <p>This is an I/O operation and will block until complete. It must* not be called from the main application thread. A blocked call will be canceled with* {@link IOException} if {@link #close} is called from another thread.** <p class="note">Requires the {@link android.Manifest.permission#NFC} permission.** @param data command bytes to send, must not be null* @return response bytes received, will not be null* @throws TagLostException if the tag leaves the field* @throws IOException if there is an I/O failure, or this operation is canceled*/public byte[] transceive(byte[] data) throws IOException { return transceive(data, true);}

小結：
我們通過開源項目NFCard、Google的Sample之CardReader、交通信息中心的《城市公共交通IC卡技術規范》文檔，成功讀出了羊城通余額。

這里需要提醒的是，最新版的NFCard源碼讀不出我手中的羊城通，顯示為未知卡片，反而找到2013年的版本才讀出來，本人手中的卡有效期也是2013年-2018年。這樣估計是各版本的卡有所不同。

接下來就是讀取卡片的卡號、有效期、交易記錄這些信息，并且解析數據，顯示在界面上。

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