是否可以读取然后写入然后再次读回我们在NFC标签上写的相同数据而不从Android中的字段（移动）中删除它？如果有人这样做了，那么请在这里分享....
public class MainActivity extends Activity
{
NfcAdapter adapter;
PendingIntent pendingIntent;
IntentFilter writeTagFilters[];
Tag mytag;
private TextView mTextViewData;
Context ctx;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ctx=this;
mTextViewData = (TextView)findViewById(R.id.mtextView);
Button btnWrite = (Button) findViewById(R.id.write_button);
final EditText mEditText = (EditText)findViewById(R.id.edit_message);
adapter = NfcAdapter.getDefaultAdapter(this);
pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
IntentFilter tagDetected1 = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED);
try
{
tagDetected1.addDataType("text/nfc-service-tag");
}
catch (MalformedMimeTypeException e)
{
throw new RuntimeException("Could not add MIME type.", e);
}
writeTagFilters = new IntentFilter[] { tagDetected1 };
btnWrite.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
if(mytag==null)
{
Toast.makeText(ctx, ctx.getString(R.string.error_detected), Toast.LENGTH_LONG ).show();
}
else
{
writeTag(mEditText.getText().toString(),mytag);
}
}
});
}
private void writeTag(String text,Tag tag)
{
// record to launch Play Store if app is not installed
// record that contains our custom "retro console" game data, using custom MIME_TYPE
String mimeType = "text/nfc-service-tag";
byte[] payload = text.getBytes(Charset.forName("US-ASCII"));
byte[] mimeBytes = mimeType.getBytes(Charset.forName("US-ASCII"));
NdefRecord record = new NdefRecord(NdefRecord.TNF_MIME_MEDIA, mimeBytes, new byte[0], payload);
NdefMessage message = new NdefMessage(new NdefRecord[] { record });
try
{
// see if tag is already NDEF formatted
Ndef ndef = Ndef.get(tag);
if (ndef != null)
{
ndef.connect();
if (!ndef.isWritable())
{
Toast.makeText(ctx, "Read-only tag.", Toast.LENGTH_LONG ).show();
}
// work out how much space we need for the data
int size = message.toByteArray().length;
if (ndef.getMaxSize() < size)
{
Toast.makeText(ctx, "Tag doesn't have enough free space.", Toast.LENGTH_LONG).show();
}
ndef.writeNdefMessage(message);
Toast.makeText(ctx, ctx.getString(R.string.ok_writing), Toast.LENGTH_LONG ).show();
ndef.close();
}
else
{
// attempt to format tag
NdefFormatable format = NdefFormatable.get(tag);
if (format != null)
{
try
{
format.connect();
format.format(message);
Toast.makeText(ctx, ctx.getString(R.string.ok_writing), Toast.LENGTH_LONG ).show();
}
catch (IOException e)
{
Toast.makeText(ctx,"Unable to format tag to NDEF.", Toast.LENGTH_LONG).show();
}
}
else
{
Toast.makeText(ctx,"Tag doesn't appear to support NDEF format.", Toast.LENGTH_LONG).show();
}
}
}
catch(Exception e)
{
}
}
@Override
protected void onNewIntent(Intent intent)
{
String action = intent.getAction();
if (action.equals(NfcAdapter.ACTION_NDEF_DISCOVERED))
{
NdefMessage[] msgs = getNdefMessagesFromIntent(intent);
final NdefMessage msg = (NdefMessage)msgs[0];
String payload = new String(msg.getRecords()[0].getPayload());
mTextViewData.setText(payload);
mytag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
Toast.makeText(this, "In onNewIntent()", Toast.LENGTH_LONG ).show();
}
else if (intent.getAction().equals(NfcAdapter.ACTION_TAG_DISCOVERED))
{
Toast.makeText(this, "This NFC tag has no NDEF data.", Toast.LENGTH_LONG).show();
}
}
@Override
public void onResume()
{
super.onResume();
if (getIntent().getAction() != null)
{
// tag received when app is not running and not in the foreground:
if (getIntent().getAction().equals(NfcAdapter.ACTION_NDEF_DISCOVERED))
{
NdefMessage[] msgs = getNdefMessagesFromIntent(getIntent());
NdefRecord record = msgs[0].getRecords()[0];
byte[] payload = record.getPayload();
String payloadString = new String(payload);
mTextViewData.setText(payloadString);
Toast.makeText(this, "In onResume()", Toast.LENGTH_LONG ).show();
}
}
adapter.enableForegroundDispatch(this, pendingIntent, writeTagFilters, null);
}
@Override
public void onPause()
{
super.onPause();
adapter.disableForegroundDispatch(this);
}
NdefMessage[] getNdefMessagesFromIntent(Intent intent)
{
// Parse the intent
NdefMessage[] msgs = null;
String action = intent.getAction();
if (action.equals(NfcAdapter.ACTION_NDEF_DISCOVERED))
{
Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
if (rawMsgs != null){
msgs = new NdefMessage[rawMsgs.length];
for (int i = 0; i < rawMsgs.length; i++)
{
msgs[i] = (NdefMessage) rawMsgs[i];
}
}
else
{
// Unknown tag type
byte[] empty = new byte[] {};
NdefRecord record = new NdefRecord(NdefRecord.TNF_UNKNOWN, empty, empty, empty);
NdefMessage msg = new NdefMessage(new NdefRecord[] { record });
msgs = new NdefMessage[] { msg };
}
}
else
{
//Log.e(TAG, "Unknown intent.");
finish();
}
return msgs;
}
}
答案 0 :(得分：2)
您可以在ndef.getNdefMessage()检查结果后立即致电ndef.writeNdefMessage(message)。它实际上会从标签中读取NDEF消息。但是，通常，当ndef.writeNdefMessage(message)不引发异常时，可以安全地假设消息已成功写入。