MainActivity.java

package com.example.puntobip;

import java.io.IOException;
import java.util.Random;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.PendingIntent;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.IntentFilter.MalformedMimeTypeException;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.MifareClassic;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private final int DIALOG_SALDO = 1;
    private final int DIALOG_CARGAR = 2;
    private final int DIALOG_NUMERO = 3;
    private final byte[] KEY_B_SECTOR_0 = new byte[]{(byte)0x1F,(byte)0xC2,(byte)0x35,(byte)0xAC,(byte)0x13,(byte)0x09};
    private final byte[] KEY_B_SECTOR_8 = new byte[]{(byte)0x64,(byte)0xE3,(byte)0xC1,(byte)0x03,(byte)0x94,(byte)0xC2};
    private final byte[] DATA_CARGA_B21 = new byte[]{(byte)0x10,(byte)0x27,(byte)0x00,(byte)0x00,(byte)0xef,(byte)0xd8,(byte)0xff,(byte)0xff,(byte)0x10,(byte)0x27,(byte)0x00,(byte)0x00,(byte)0x21,(byte)0xde,(byte)0x21,(byte)0xde};
    private final byte[] DATA_CARGA_B22 = new byte[]{(byte)0x10,(byte)0x27,(byte)0x00,(byte)0x00,(byte)0xef,(byte)0xd8,(byte)0xff,(byte)0xff,(byte)0x10,(byte)0x27,(byte)0x00,(byte)0x00,(byte)0x22,(byte)0xdd,(byte)0x22,(byte)0xdd};

    private TapDialog tapDialog;

    private NfcAdapter mNfcAdapter;
    private PendingIntent mPendingIntent;
    private IntentFilter[] mFilters;
    private String[][] mTechList;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        showTapDialog(getResources().getString(R.string.consultar_saldo), DIALOG_SALDO);
        inicializarNFC();
    }

    public void onCargarSaldo(View view) {
        showTapDialog(getResources().getString(R.string.cargar_saldo), DIALOG_CARGAR);
    }

    public void onCambiarNumero(View view) {
        showTapDialog(getResources().getString(R.string.cambiar_numero), DIALOG_NUMERO);
    }

    private void showTapDialog(String message, int tag) {
        if(tapDialog == null) {
            tapDialog = new TapDialog(this);
            tapDialog.setCanceledOnTouchOutside(false);
        }
        tapDialog.setTitle(message);
        tapDialog.setTag(tag);
        tapDialog.show();
    }

    private void inicializarNFC() {
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if (mNfcAdapter == null) {
            Toast.makeText(this, "Este dispositivo no soporta NFC.", Toast.LENGTH_LONG).show();
            finish();
            return;
        }

        if (!mNfcAdapter.isEnabled()) {
            AlertDialog alertDialog = new AlertDialog.Builder(this).create();
            alertDialog.setTitle("NFC deshabilitado");
            alertDialog.setMessage("Su NFC está deshabilitado.\nIngrese a las opciones de configuración y activelo.");
            alertDialog.show();
        }

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

        IntentFilter ndef = new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED);
        try {
            ndef.addDataType("*/*");
        } catch (MalformedMimeTypeException e) {
            throw new RuntimeException("error", e);
        }

        mFilters = new IntentFilter[] {ndef};
        mTechList = new String[][] { new String[] { MifareClassic.class.getName() } };
    }

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

        mNfcAdapter.enableForegroundDispatch(this, mPendingIntent, mFilters, mTechList);
    }

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

        mNfcAdapter.disableForegroundDispatch(this);
    }

    @Override
    protected void onNewIntent(Intent intent) {
        String action = intent.getAction();

        if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {
            Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            MifareClassic mfc = MifareClassic.get(tagFromIntent);

            try {
                mfc.connect();

                if(tapDialog.isShowing()) {
                    switch (tapDialog.getTag()) {
                    case DIALOG_CARGAR:
                        if(mfc.authenticateSectorWithKeyB(0x08, KEY_B_SECTOR_8)) {
                            mfc.writeBlock(0x21, DATA_CARGA_B21);
                            mfc.writeBlock(0x22, DATA_CARGA_B22);
                        } else {
                            Toast.makeText(this, "error autenticando sector 0x21", Toast.LENGTH_LONG).show();
                        }
                        break;

                    case DIALOG_NUMERO:
                        if(mfc.authenticateSectorWithKeyB(0x00, KEY_B_SECTOR_0)) {
                            byte[] data = mfc.readBlock(0x01);
                            Random rand = new Random();
                            data[4] = (byte) (rand.nextInt((0xff - 0x00) + 1) + 0x00);
                            data[5] = (byte) (rand.nextInt((0xff - 0x00) + 1) + 0x00);
                            data[6] = (byte) (rand.nextInt((0xff - 0x00) + 1) + 0x00);
                            data[7] = (byte) (rand.nextInt((0xff - 0x00) + 1) + 0x00);
                            mfc.writeBlock(0x01, data);
                        } else {
                            Toast.makeText(this, "error autenticando sector 0x00", Toast.LENGTH_LONG).show();
                        }
                        break;
                    }
                }

                //
                // datos de la tarjeta
                // ----------------------------------------------------------------
                //
                TextView tvNumeroUUID = (TextView)findViewById(R.id.tvNumeroUUID);
                TextView tvNumeroBIP = (TextView)findViewById(R.id.tvNumeroBIP);
                TextView tvSaldoBIP = (TextView)findViewById(R.id.tvSaldoBIP);

                // uuid
                tvNumeroUUID.setText(leToNumericString(mfc.getTag().getId(), 4));

                // numero bip
                if(mfc.authenticateSectorWithKeyB(0x00, KEY_B_SECTOR_0)) {
                    byte[] data = mfc.readBlock(0x01);
                    tvNumeroBIP.setText(leToNumericString(new byte[]{data[4],data[5],data[6],data[7]}, 4));
                } else {
                    Toast.makeText(this, "error autenticando sector 0x00", Toast.LENGTH_LONG).show();
                }

                // saldo bip
                if(mfc.authenticateSectorWithKeyB(0x08, KEY_B_SECTOR_8)) {
                    byte[] data = mfc.readBlock(0x21);
                    tvSaldoBIP.setText(formatMoneda(leToNumeric(data, 2)));
                } else {
                    Toast.makeText(this, "error autenticando sector 0x21", Toast.LENGTH_LONG).show();
                }

            } catch (Exception e) {
                Log.e("error", e.getLocalizedMessage());
                Toast.makeText(this, e.getLocalizedMessage(), Toast.LENGTH_LONG).show();
            } finally {
                try {mfc.close();} catch (IOException e) {}
            }
        }

        tapDialog.dismiss();
    }

    private long leToNumeric(byte[] buffer, int size) {
        long value = 0;
        for (int i=0; i<size; i++) { value += ((long) buffer[i] & 0xffL) << (8 * i); }
        return value;
    }

    private String leToNumericString(byte[] buffer, int size) {
        return String.valueOf(leToNumeric(buffer, size));
    }

    private String formatMoneda(long valor) {
        return "$"+String.format("%,d", valor);
    }
}