当我尝试写入 NFC 标签时出现标签丢失异常

Question

我希望有人能告诉我我在这里缺少什么。也许这是我的连接方式。我的标签实际上是 Mifare Ultralight，所以我没有弄错。我调试了，连接到标签是成功的——一切似乎都很好。但是日志一直在说：

android.nfc.TagLostException: 标签丢失。

public class MainActivity extends Activity {

    NfcAdapter mNfcAdapter;
    TextView displayInfo;
    Tag mNfcTag;
    NdefMessage mNdefMessage;

    IntentFilter [] intentFiltersArray;

    String [] [] techListsArray;

    PendingIntent pendingIntent;


    String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        displayInfo = (TextView) findViewById(R.id.displayInfo);

        NdefRecord application = NdefRecord.createApplicationRecord("com.studios.nfcdemo");


        Locale locale = new Locale("en");

        NdefRecord textText = createTextRecord("pleaseWork", locale, true);

        mNdefMessage = new NdefMessage(textText);

        pendingIntent = PendingIntent.getActivity(
                this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);

        IntentFilter ndef = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED);
        try {
            ndef.addDataType("*/*");    /* Handles all MIME based dispatches.
                                       You should specify only the ones that you need. */
        }
        catch (IntentFilter.MalformedMimeTypeException e) {
            throw new RuntimeException("fail", e);
        }

        intentFiltersArray = new IntentFilter[] {ndef};

        techListsArray = new String[][] { new String[] { MifareUltralight.class.getName() } };




    }
    public NdefRecord createTextRecord(String payload, Locale locale, boolean encodeInUtf8) {
        byte[] langBytes = locale.getLanguage().getBytes(Charset.forName("US-ASCII"));
        Charset utfEncoding = encodeInUtf8 ? Charset.forName("UTF-8") : Charset.forName("UTF-16");
        byte[] textBytes = payload.getBytes(utfEncoding);
        int utfBit = encodeInUtf8 ? 0 : (1 << 7);
        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;
    }

    @Override
    public void onNewIntent(Intent intent) {
        Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
        MifareUltralight ultralight = MifareUltralight.get(tagFromIntent);
        write(ultralight);
    }


    private void write(MifareUltralight lol) {
        try{
            lol.connect();
            lol.writePage(0, "please work".getBytes(Charset.forName("US-ASCII")));
            Toast.makeText(this, "Tag written", Toast.LENGTH_LONG).show();

        }
        catch (Exception e){
            Log.d(TAG, "no  " + e.toString());
        }
        finally{
            try{
                lol.close();
            }
            catch (Exception e){
                Log.d(TAG, e.toString());
            }
        }
    }

    public void onPause() {
        super.onPause();
        mNfcAdapter.disableForegroundDispatch(this);
    }

    public void onResume() {
        super.onResume();
        mNfcAdapter.enableForegroundDispatch(this, pendingIntent, intentFiltersArray, techListsArray);
    }
}

Answer 1

您调用 writePage() 方法有两个问题：

MIFARE Ultralight 标签的第 0 页是只读的。您不能写入该页面。这同样适用于第 1 页和第 2 页的部分内容（尽管对第 2 页的写命令应该成功并且将设置锁定位）。
写入命令需要 4 个字节（正好 4 个字节，不多也不少）但您尝试传递 11 个字节（"please work"在 US-ASCII 中）。

Answer 2

我发现了我的错误。我想编写 Ndef 消息并使用标签，因为 MifareUltralight 有点傻，因为它只会使一切复杂化。相反，我将标签转换为 Ndef。这是我的代码：

private void write(Tag tag) {
        Ndef ndef = Ndef.get(tag);
        Locale locale = Locale.ENGLISH;
        NdefRecord hi = createTextRecord("hello world", locale, true);
        mNdefMessage = new NdefMessage(hi);

        try{
            ndef.connect();
            ndef.writeNdefMessage(mNdefMessage);
            Toast.makeText(this, "Message Written", Toast.LENGTH_LONG).show();
        }
        catch (Exception e){
            Log.d(TAG, "Exception:  " + e.toString());
        }
        finally {
            try{
                ndef.close();
            }
            catch(Exception e){
                Log.d(TAG, ":( no  " + e.toString());
            }
        }
    }

如果有人需要弄清楚如何创建文本记录（以 UTF 8 编码）并从 Ndef 支持的标签中读取，我也为这些添加了我的方法：

正在创建文本记录：

public NdefRecord createTextRecord(String payload, Locale locale, boolean encodeInUtf8) {
    byte[] langBytes = locale.getLanguage().getBytes(Charset.forName("US-ASCII"));
    Charset utfEncoding = encodeInUtf8 ? Charset.forName("UTF-8") : Charset.forName("UTF-16");
    byte[] textBytes = payload.getBytes(utfEncoding);
    int utfBit = encodeInUtf8 ? 0 : (1 << 7);
    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;
}

正在读取 NDEF 标签：

private void read(Tag tagFromIntent) {
    Ndef ndef = Ndef.get(tagFromIntent);

    try{
        ndef.connect();
        mNdefMessage = ndef.getNdefMessage();
        NdefRecord [] records = mNdefMessage.getRecords();
        byte [] payload = records[0].getPayload();
        String displayString = getTextFromNdefRecord(records[0]);
        displayInfo.setText(displayString);
        Toast.makeText(this, "String read", Toast.LENGTH_LONG).show();
    }
    catch (Exception e){
        Log.d(TAG, e.toString());
    }
    finally {
        try{
            ndef.close();
        }
        catch (Exception e){
            Log.d(TAG, e.toString());
        }
    }

正在从 NdefRecords 读取文本：

 public String getTextFromNdefRecord(NdefRecord ndefRecord)
{
    String tagContent = null;
    try {
        byte[] payload = ndefRecord.getPayload();
        String textEncoding = "UTF-8";
        int languageSize = payload[0] & 0063;
        tagContent = new String(payload, languageSize + 1,
                payload.length - languageSize - 1, textEncoding);
    } catch (UnsupportedEncodingException e) {
        Log.e("getTextFromNdefRecord", e.getMessage(), e);
    }
    return tagContent;
}

我希望这对其他使用 NFC 的人有所帮助。这些简单的方法应该在 Android 内为您提供所需的所有功能。

当我尝试写入 NFC 标签时出现标签丢失异常

I'm getting a tag lost exception when I try writing to an NFC tag

android

tags

nfc

mifare