connection to a NFC-tag in an android app

I'm trying to write an android app for may Nexus S that is able to write a simple Text Record on a NFC-Tag. My problem is the connection-establishment to the NFC-Tag. I've implemented two activities called "TagWriter" & "TagWriterStartPage".

Here ist the "TagWriter"-activity:

package nfc.example.writer;

import java.util.Locale;

import c开发者_如何学JAVAom.google.common.base.Charsets;
import com.google.common.primitives.Bytes;

import android.app.Activity;
import android.content.Intent;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.Ndef;
import android.nfc.tech.NdefFormatable;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class TagWriter extends Activity 
{

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tagwriter);

        Intent intent = this.getIntent();

        Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
        writeTag(tag);
    }

    private void writeTag(Tag t) 
    {
        Ndef tag = Ndef.get(t);  
        Locale locale = Locale.US;
        final byte[] langBytes = locale.getLanguage().getBytes(Charsets.US_ASCII);
        String text = "Tag, you're it!";
        final byte[] textBytes = text.getBytes(Charsets.UTF_8);
        final int utfBit = 0;
        final char status = (char) (utfBit + langBytes.length);
        final byte[] data = Bytes.concat(new byte[] {(byte) status}, langBytes, textBytes);
        NdefRecord record = new NdefRecord(NdefRecord.TNF_WELL_KNOWN, NdefRecord.RTD_TEXT, new byte[0], data);
        try 
        {
            NdefRecord[] records = {record};
            NdefMessage message = new NdefMessage(records);
            tag.connect();
            boolean connected = tag.isConnected();
            boolean writeable = tag.isWritable();
            if( connected && writeable)
            {   
                tag.writeNdefMessage(message);
            }
            tag.close();
        }
        catch (Exception e)
        {
            //do error handling
        }
    }
}

The activity "TagWriter" is called when I put my device on the NFC-tag. Everytime the method "tag.connect()" is called, there occures an exception.

Can anyone help me to solve the problem???

Thanks, Dennis

this might work better:

Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
Ndef ndef = Ndef.get(tag);
if (ndef != null) {
  ndef.connect();
  ndef.writeNdefMessage(message);
} else {
  NdefFormatable format = NdefFormatable.get(tag);
  if (format != null) {
    format.connect();
    format.format(message);
  }           
}

need other checks in there for real use (capacity, writable etc) - but that is bare bones..