⭐ Android NFC Tag Rewrite: Delete Existing NDEF and Write New Text

Android developers often face an issue where existing NDEF data remains on an NFC tag, preventing new data from being written correctly. This article explains how to delete old NDEF records and write new text data safely using NdefFormatable and Ndef.

This guide covers:

How to remove existing NDEF data
How to write a new Text record
How to check write permissions
How to verify the written data
Common mistakes and how to avoid them

All code examples are based on your verified implementation.

Contents

1. Why Existing NDEF Data Remains on NFC Tags
2. How to Delete Existing NDEF Data (NdefFormatable / Ndef)
3. Create a New Text Record (UTF‑8)
4. Complete Write Process (Full Code)
5. Common Mistakes and How to Fix Them
6. Summary: Formatting Is the Key to Safe NFC Rewrite

1. Why Existing NDEF Data Remains on NFC Tags

Some NFC tags append new NDEF records instead of overwriting existing ones. This causes:

Old data remaining on the tag
New data not appearing
Multiple records returned when reading

To avoid this, you must format or overwrite the tag properly.

2. How to Delete Existing NDEF Data (NdefFormatable / Ndef)

✔ If the tag is NDEF‑formatable

java

NdefFormatable formatable = NdefFormatable.get(tag);
if (formatable != null) {
    formatable.format(message);  // Format and write new data
}

✔ If the tag already supports NDEF

java

Ndef ndef = Ndef.get(tag);
ndef.connect();
ndef.writeNdefMessage(message);  // Overwrite existing data
ndef.close();

✔ Always check writability before writing

java

if (!ndef.isWritable()) {
    // Tag is not writable
}

3. Create a New Text Record (UTF‑8)

java

String text = "Hello NFC";
byte[] lang = "en".getBytes(Charset.forName("US-ASCII"));
byte[] textBytes = text.getBytes(Charset.forName("UTF-8"));

byte[] payload = new byte[1 + lang.length + textBytes.length];
payload[0] = (byte) lang.length;

System.arraycopy(lang, 0, payload, 1, lang.length);
System.arraycopy(textBytes, 0, payload, 1 + lang.length, textBytes.length);

NdefRecord record = new NdefRecord(
        NdefRecord.TNF_WELL_KNOWN,
        NdefRecord.RTD_TEXT,
        new byte[0],
        payload
);

NdefMessage message = new NdefMessage(new NdefRecord[]{record});

4. Complete Write Process (Full Code)

java

public void writeTag(Tag tag, String text) {

    NdefMessage message = createTextMessage(text);

    NdefFormatable formatable = NdefFormatable.get(tag);
    if (formatable != null) {
        try {
            formatable.format(message);
            return;
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    Ndef ndef = Ndef.get(tag);
    if (ndef != null) {
        try {
            ndef.connect();
            if (!ndef.isWritable()) return;
            ndef.writeNdefMessage(message);
            ndef.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}