在asp中使用变量和常量

前面例子介绍了检测，读写NFC TAG开发的一般步骤，本例针对常用的Mifare Tag 具体说明。

Mifare Tag 可以有1K ,2K, 4K，其内存分区大同小异，下图给出了1K字节容量的Tag的内存分布:





数据分为16个区(Sector) ,每个区有4个块(Block) ，每个块可以存放16字节的数据，其大小为16 X 4 X 16 =1024 bytes

每个区最后一个块称为Trailer ，主要用来存放读写该区Block数据的Key ，可以有A，B两个Key，每个Key 长度为6个字节，缺省的Key值一般为全FF或是0. 由 MifareClassic.KEY_DEFAULT 定义。

因此读写Mifare Tag 首先需要有正确的Key值（起到保护的作用），如果鉴权成功

auth = mfc.authenticateSectorWithKeyA(j,

MifareClassic.KEY_DEFAULT);

然后才可以读写该区数据。

本例定义几个Mifare相关的类 MifareClassCard ，MifareSector, MifareBlock 和MifareKey 以方便读写Mifare Tag.

Android 系统来检测到NFC Tag， 将其封装成Tag类，存放到Intent的NfcAdapter.EXTRA_TAG Extra 数据包中，可以使用MifareClassic.get(Tag) 获取对象的 MifareClassic类。

Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
// 4) Get an instance of the Mifare classic card from this TAG
// intent
MifareClassic mfc = MifareClassic.get(tagFromIntent);

下面为读取Mifare card 的主要代码：

// 1) Parse the intent and get the action that triggered this intent
String action = intent.getAction();
// 2) Check if it was triggered by a tag discovered interruption.
if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {
// 3) Get an instance of the TAG from the NfcAdapter
Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
// 4) Get an instance of the Mifare classic card from this TAG
// intent
MifareClassic mfc = MifareClassic.get(tagFromIntent);
MifareClassCard mifareClassCard=null;

try { // 5.1) Connect to card
mfc.connect();
boolean auth = false;
// 5.2) and get the number of sectors this card has..and loop
// thru these sectors
int secCount = mfc.getSectorCount();
mifareClassCard= new MifareClassCard(secCount);
int bCount = 0;
int bIndex = 0;
for (int j = 0; j < secCount; j++) {
MifareSector mifareSector = new MifareSector();
mifareSector.sectorIndex = j;
// 6.1) authenticate the sector
auth = mfc.authenticateSectorWithKeyA(j,
MifareClassic.KEY_DEFAULT);
mifareSector.authorized = auth;
if (auth) {
// 6.2) In each sector - get the block count
bCount = mfc.getBlockCountInSector(j);
bCount =Math.min(bCount, MifareSector.BLOCKCOUNT);
bIndex = mfc.sectorToBlock(j);
for (int i = 0; i < bCount; i++) {

// 6.3) Read the block
byte []data = mfc.readBlock(bIndex);
MifareBlock mifareBlock = new MifareBlock(data);
mifareBlock.blockIndex = bIndex;
// 7) Convert the data into a string from Hex
// format.

bIndex++;
mifareSector.blocks[i] = mifareBlock;

}
mifareClassCard.setSector(mifareSector.sectorIndex,
mifareSector);
} else { // Authentication failed - Handle it

}
}
ArrayList<String> blockData=new ArrayList<String>();
int blockIndex=0;
for(int i=0;i<secCount;i++){

MifareSector mifareSector=mifareClassCard.getSector(i);
for(int j=0;j<MifareSector.BLOCKCOUNT;j++){
MifareBlock mifareBlock=mifareSector.blocks[j];
byte []data=mifareBlock.getData();
blockData.add("Block "+ blockIndex++ +" : "+
Converter.getHexString(data, data.length));
}
}
String []contents=new String[blockData.size()];
blockData.toArray(contents);
setListAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, contents));
getListView().setTextFilterEnabled(true);

} catch (IOException e) {
Log.e(TAG, e.getLocalizedMessage());
showAlert(3);
}finally{

if(mifareClassCard!=null){
mifareClassCard.debugPrint();
}
}
}// End of method

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