为什么我会收到反向的 NFC 标签 ID（十六进制）？

Question

I want my app to scan an NFC tag and get its ID and tag type. But somehow my code reads a reversed tag ID.

For instance my app reads the following tag ID (hex): 80 65 69 e2 f5 fe 04 while 4 other similar apps from Google Play Store read the following ID: 4 fe f5 e2 69 65 80 (where the first zero is also missing)

I want my app to read the tag ID without reverting the bytes, how can I achieve that? Here is my complete code:

package com.asetnfc;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.Intent;
import android.content.IntentFilter;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.IsoDep;
import android.nfc.tech.MifareClassic;
import android.nfc.tech.MifareUltralight;
import android.nfc.tech.Ndef;
import android.nfc.tech.NfcA;
import android.nfc.tech.NfcB;
import android.nfc.tech.NfcF;
import android.nfc.tech.NfcV;
import android.os.AsyncTask;
import android.os.Parcelable;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.widget.TextView;
import android.widget.Toast;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Date;


import static android.content.ContentValues.TAG;

//public class MainActivity extends AppCompatActivity {

public class InfoNFC extends Activity {
    private TextView mTextView; //ECP 2017-01-16

    // list of NFC technologies detected:
    private final String[][] techList = new String[][] {
            new String[] {
                    NfcA.class.getName(),
                    NfcB.class.getName(),
                    NfcF.class.getName(),
                    NfcV.class.getName(),
                    IsoDep.class.getName(),
                    MifareClassic.class.getName(),
                    MifareUltralight.class.getName(), Ndef.class.getName()
            }
    };

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

        mTextView = (TextView) findViewById(R.id.infonfctype);
        mTextView.setText("Data Tampil Disini");
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d("onResume", "1");

        //mTextView.setText("onResume:");
        // creating pending intent:
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
        // creating intent receiver for NFC events:
        IntentFilter filter = new IntentFilter();
        filter.addAction(NfcAdapter.ACTION_TAG_DISCOVERED);
        filter.addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
        filter.addAction(NfcAdapter.ACTION_TECH_DISCOVERED);
        // enabling foreground dispatch for getting intent from NFC event:
        NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
        nfcAdapter.enableForegroundDispatch(this, pendingIntent, new IntentFilter[]{filter}, this.techList);
    }

    @Override
    protected void onPause() {
        super.onPause();

        Log.d("onPause", "1");

        // disabling foreground dispatch:
        NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
        nfcAdapter.disableForegroundDispatch(this);
    }

    @Override
    protected void onNewIntent(Intent intent) {
        Log.d("onNewIntent", "1");

        if (intent.getAction().equals(NfcAdapter.ACTION_TAG_DISCOVERED)) {
            Log.d("onNewIntent", "2");
            mTextView.setText( "NFC Tag\n" + ByteArrayToHexString(intent.getByteArrayExtra(NfcAdapter.EXTRA_ID)));

            //if(getIntent().hasExtra(NfcAdapter.EXTRA_TAG)){

            Parcelable tagN = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            if (tagN != null) {
                Log.d(TAG, "Parcelable OK");
                NdefMessage[] msgs;
                byte[] empty = new byte[0];
                byte[] id = intent.getByteArrayExtra(NfcAdapter.EXTRA_ID);
                byte[] payload = dumpTagData(tagN).getBytes();
                NdefRecord record = new NdefRecord(NdefRecord.TNF_UNKNOWN, empty, id, payload);
                NdefMessage msg = new NdefMessage(new NdefRecord[] { record });
                msgs = new NdefMessage[] { msg };

                //Log.d(TAG, msgs[0].toString());


            }
            else {
                Log.d(TAG, "Parcelable NULL");
            }



            Parcelable[] messages1 = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
            if (messages1 != null) {
                Log.d(TAG, "Found " + messages1.length + " NDEF messages");
            }
            else {
                Log.d(TAG, "Not EXTRA_NDEF_MESSAGES");
            }

            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            Ndef ndef = Ndef.get(tag);
            if(ndef != null) {

                Log.d("onNewIntent:", "NfcAdapter.EXTRA_TAG");

                Parcelable[] messages = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
                if (messages != null) {
                    Log.d(TAG, "Found " + messages.length + " NDEF messages");
                }
            }
            else {
                Log.d(TAG, "Write to an unformatted tag not implemented");
            }


            //mTextView.setText( "NFC Tag\n" + ByteArrayToHexString(intent.getByteArrayExtra(NfcAdapter.EXTRA_TAG)));
        }
    }

    private String dumpTagData(Parcelable p) {
        StringBuilder sb = new StringBuilder();
        Tag tag = (Tag) p;
        byte[] id = tag.getId();
        sb.append("Tag ID (hex): ").append(getHex(id)).append("\n");
        sb.append("Tag ID (dec): ").append(getDec(id)).append("\n");



        String prefix = "android.nfc.tech.";
        sb.append("Technologies: ");
        for (String tech : tag.getTechList()) {
            sb.append(tech.substring(prefix.length()));
            sb.append(", ");
        }
        sb.delete(sb.length() - 2, sb.length());
        for (String tech : tag.getTechList()) {
            if (tech.equals(MifareClassic.class.getName())) {
                sb.append('\n');
                MifareClassic mifareTag = MifareClassic.get(tag);
                String type = "Unknown";
                switch (mifareTag.getType()) {
                    case MifareClassic.TYPE_CLASSIC:
                        type = "Classic";
                        break;
                    case MifareClassic.TYPE_PLUS:
                        type = "Plus";
                        break;
                    case MifareClassic.TYPE_PRO:
                        type = "Pro";
                        break;
                }
                sb.append("Mifare Classic type: ");
                sb.append(type);
                sb.append('\n');

                sb.append("Mifare size: ");
                sb.append(mifareTag.getSize() + " bytes");
                sb.append('\n');

                sb.append("Mifare sectors: ");
                sb.append(mifareTag.getSectorCount());
                sb.append('\n');

                sb.append("Mifare blocks: ");
                sb.append(mifareTag.getBlockCount());
            }

            if (tech.equals(MifareUltralight.class.getName())) {
                sb.append('\n');
                MifareUltralight mifareUlTag = MifareUltralight.get(tag);
                String type = "Unknown";
                switch (mifareUlTag.getType()) {
                    case MifareUltralight.TYPE_ULTRALIGHT:
                        type = "Ultralight";
                        break;
                    case MifareUltralight.TYPE_ULTRALIGHT_C:
                        type = "Ultralight C";
                        break;
                }
                sb.append("Mifare Ultralight type: ");
                sb.append(type);
            }
        }
        Log.d("Datos: ", sb.toString());



        mTextView.setText('\n' + sb.toString());
        return sb.toString();
    }


    private String getHex(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (int i = bytes.length - 1; i >= 0; --i) {
            int b = bytes[i] & 0xff;
            if (b < 0x10)
                sb.append('0');
            sb.append(Integer.toHexString(b));
            if (i > 0) {
                sb.append(" ");
            }
        }
        return sb.toString();
    }

    private long getDec(byte[] bytes) {
        long result = 0;
        long factor = 1;
        for (int i = 0; i < bytes.length; ++i) {
            long value = bytes[i] & 0xffl;
            result += value * factor;
            factor *= 256l;
        }
        return result;
    }



    private String ByteArrayToHexString(byte [] inarray) {

        Log.d("ByteArrayToHexString", inarray.toString());

        int i, j, in;
        String [] hex = {"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};
        String out= "";

        for(j = 0 ; j < inarray.length ; ++j)
        {
            in = (int) inarray[j] & 0xff;
            i = (in >> 4) & 0x0f;
            out += hex[i];
            i = in & 0x0f;
            out += hex[i];
        }
//CE7AEED4
//EE7BEED4
        Log.d("ByteArrayToHexString", String.format("%0" + (inarray.length * 2) + "X", new BigInteger(1,inarray)));


        return out;
    }

}

Answer 1

In your function getHex() you are starting from last byte and then decrementing the i counter. try to use this function:

private final static char[] hexArray = "0123456789ABCDEF".toCharArray();
public static String bytesToHexString(byte[] bytes) {
    if (bytes == null) {
        return null;
    }
    char[] hexChars = new char[bytes.length * 2];
    for (int j = 0; j < bytes.length; j++) {
        int v = bytes[j] & 0xFF;
        hexChars[j * 2] = hexArray[v >>> 4];
        hexChars[j * 2 + 1] = hexArray[v & 0x0F];
    }
    return new String(hexChars);
}