Logran crear una aplicación para cargar tarjeta bip!

package com.example.puntobip;

import java.io.IOException;

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.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private final String MONTO_DEFAULT = "2000";
   
    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);
        tapDialog = new TapDialog(this, getResources().getString(R.string.consultar_saldo)).display();
        inicializarNFC();
    }
   
    public void onCargarSaldo(View view) {
        String txtSaldo = ((TextView)findViewById(R.id.tvSaldoBIP)).getText().toString().replace("$", "");
        tapDialog = new TapDialog(this, getResources().getString(R.string.cargar_saldo)).displayCargar(txtSaldo.isEmpty() ? MONTO_DEFAULT : txtSaldo);
    }
   
    public void onCambiarNumero(View view) {
        TextView tvNumeroBIP = (TextView)findViewById(R.id.tvNumeroBIP);
        tapDialog = new TapDialog(this, getResources().getString(R.string.cambiar_numero)).displayNumero(tvNumeroBIP.getText().toString());
    }
   
    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 esta deshabilitado.\nIngrese a las opciones de configuracion 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);
            MifareManager mifare = new MifareManager(tagFromIntent);
           
            try {
                mifare.open();
                if(tapDialog.isShowing()) {
                    procesarOperacion(tapDialog, mifare);
                }
                desplegarDatosTarjeta(mifare);
            } catch (AuthenticateException e) {
                Log.e("error", "error autenticando sector", e);
                Toast.makeText(this, "error autenticando sector " + e.getSector(), Toast.LENGTH_LONG).show();
            } catch (Exception e) {
                Log.e("error", "error desconocido", e);
                Toast.makeText(this, e.getMessage(), Toast.LENGTH_LONG).show();
            } finally {
                if(tapDialog != null) tapDialog.dismiss();
                mifare.close();
            }
           
        }
    }
   
    /**
     * Despliega datos de tarjeta
     * @param mifare
     * @throws IOException
     * @throws AuthenticateException
     */
    private void desplegarDatosTarjeta(MifareManager mifare) throws IOException, AuthenticateException {
        TextView tvNumeroUUID = (TextView)findViewById(R.id.tvNumeroUUID);
        TextView tvNumeroBIP = (TextView)findViewById(R.id.tvNumeroBIP);
        TextView tvSaldoBIP = (TextView)findViewById(R.id.tvSaldoBIP);
        byte[] data;
       
        // uuid
        tvNumeroUUID.setText(Utils.leToNumericString(mifare.getTag().getId(), 4));
       
        // numero bip
        data = mifare.readBlock(0x01);
        tvNumeroBIP.setText(Utils.leToNumericString(new byte[]{data[4],data[5],data[6],data[7]}, 4));
       
        // saldo bip
        data = mifare.readBlock(0x21);
        tvSaldoBIP.setText(Utils.formatMoneda(Utils.leToNumeric(data, 2)));
    }
   
    /**
     * Procesa una operacion sobre la tarjeta
     * @param tapDialog
     * @param mifare
     * @throws IOException
     * @throws AuthenticateException
     */
    private void procesarOperacion(TapDialog tapDialog, MifareManager mifare) throws IOException, AuthenticateException {
        switch (tapDialog.getTag()) {
       
        case Constants.DIALOG_CARGAR:
            String txtMontoCargar = ((EditText)tapDialog.findViewById(R.id.etMontoCargar)).getText().toString();
            int montoCargar = (txtMontoCargar.length() == 0) ? 0 : Integer.parseInt(txtMontoCargar);
           
            mifare.writeValue(0x21, montoCargar);
            mifare.writeValue(0x22, montoCargar);
            break;

        case Constants.DIALOG_NUMERO:
            String txtNumeroBip = ((EditText)tapDialog.findViewById(R.id.etNumeroBip)).getText().toString();
            long numeroBip = (txtNumeroBip.length() == 0) ? 0 : Long.parseLong(txtNumeroBip);
           
            byte[] data = mifare.readBlock(0x01);
            data[4] = (byte) (numeroBip >>> 0);
            data[5] = (byte) (numeroBip >>> 8);
            data[6] = (byte) (numeroBip >>> 16);
            data[7] = (byte) (numeroBip >>> 24);
            mifare.writeBlock(0x01, data);
            break;
       
        }
    }
   
}