如何将 NDEF 记录写入 NFC 标签? [英] How to write NDEF records to NFC tag?

问题描述

如何将 NDEF 消息写入 NFC 标签?我必须更改清单文件吗?到目前为止，我有生成 NDEF 消息的代码:

How do I write NDEF message to NFC tag? Do I have to change manifest file? So far I have code to generate NDEF message:

    public NdefRecord createTextRecord(String payload, Locale locale, boolean encodeInUtf8) {
    byte[] langBytes = locale.getLanguage().getBytes(Charset.forName("US-ASCII"));
    Charset utfEncoding = encodeInUtf8 ? Charset.forName("UTF-8") : Charset.forName("UTF-16");
    byte[] textBytes = payload.getBytes(utfEncoding);
    int utfBit = encodeInUtf8 ? 0 : (1 << 7);
    char status = (char) (utfBit + langBytes.length);
    byte[] data = new byte[1 + langBytes.length + textBytes.length];
    data[0] = (byte) status;
    System.arraycopy(langBytes, 0, data, 1, langBytes.length);
    System.arraycopy(textBytes, 0, data, 1 + langBytes.length, textBytes.length);
    NdefRecord record = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,
            NdefRecord.RTD_TEXT, new byte[0], data);
    return record;
}

我如何发现 TAG?有人可以帮我吗?

How do I discover the TAG? Can someone help me with that?

推荐答案

我会忽略在 https://developer.android.com/guide/topics/connectivity/nfc/nfc 和在 https://developer.android.com/guide/topics/connectivity/nfc/advanced-nfc#read-write，因为这为写入标签提供了非常差的用户体验，并由于用户行为导致大量写入失败.

I would ignore what the Google documentation says for reading at https://developer.android.com/guide/topics/connectivity/nfc/nfc and for read/write at https://developer.android.com/guide/topics/connectivity/nfc/advanced-nfc#read-write as this provides a very poor user experience for writing to Tags and leads to a lot of failed writes because of user behaviour.

要使用 Android 可靠地写入 NFC，您应该使用更新更好的 enableReaderMode API https://developer.android.com/reference/android/nfc/NfcAdapter

To get reliable writing to NFC with Android you should use the newer and much better enableReaderMode API https://developer.android.com/reference/android/nfc/NfcAdapter

使用这个较新的 API 会导致写入失败和卡损坏的情况减少很多，因为您可以控制通知声音何时发生.使用旧的基于Intent的系统，系统应用程序会暂停您的应用程序，然后读取卡片并发出通知声音，然后用户在您的应用程序恢复之前采用卡片方式并有机会处理卡片数据并写入卡中.

Using this newer API leads to a lot less failed writes and corrupted cards because you can control when the notification sound happens. With the old Intent based system the system App pauses your app and then reads the card and makes a notification sound, the user then takes the card way before your App is resumed and has a chance to handle the card data and write to the card.

使用较新的enableReaderMode API，您可以关闭系统通知声音，并且您的应用程序永远不会暂停读取NFC卡，然后您可以读写卡，然后当您成功写入时您可以自己发出通知声音.

With the newer enableReaderMode API you turn off the system notification sound and your App is never paused to read the NFC card, you can then read and write to the card and then when you have successfully written to the card you can make the notification sound yourself.

因为任何错误都是无声的，所以用户会不断尝试出示卡片，直到成功通知.需要额外的逻辑来避免每次出示单张卡片或出示不同卡片时都写入相同的消息.

Because any errors are silent, the user will keep trying to present the card until the success Notification. Additional logic is needed not to write the same message to every time a single card is presented or when different cards are presented.

一些示例代码(改编自我的应用程序，NFC 低级读写(不是 Ndef 标签技术))

Some example code (adapted from my app the does NFC low level reading and writing (not Ndef Tag technology))

public class NFCActivity extends AppCompatActivity implements NfcAdapter.ReaderCallback{

private NfcAdapter mNfcAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_nfc);

        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

        // Rest of Activity setup
     }

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

        if(mNfcAdapter!= null) {
            Bundle options = new Bundle();
            // Work around for some broken Nfc firmware implementations that poll the card too fast
            options.putInt(NfcAdapter.EXTRA_READER_PRESENCE_CHECK_DELAY, 250);

            // Enable ReaderMode for all types of card and disable platform sounds
            mNfcAdapter.enableReaderMode(this,
                    this,
                    NfcAdapter.FLAG_READER_NFC_A |
                            NfcAdapter.FLAG_READER_NFC_B |
                            NfcAdapter.FLAG_READER_NFC_F |
                            NfcAdapter.FLAG_READER_NFC_V |
                            NfcAdapter.FLAG_READER_NFC_BARCODE |
                            NfcAdapter.FLAG_READER_NO_PLATFORM_SOUNDS,
                    options);
        }

    }

    @Override
    protected void onPause() {
        super.onPause();
        if(mNfcAdapter!= null)
            mNfcAdapter.disableReaderMode(this);
    }
    
   // This method is run in another thread when a card is discovered
   // !!!! This method cannot cannot direct interact with the UI Thread
   // Use `runOnUiThread` method to change the UI from this method
   public void onTagDiscovered(Tag tag) {

      // Read and or write to Tag here to the appropriate Tag Technology type class
      // in this example the card should be an Ndef Technology Type 
      Ndef mNdef = Ndef.get(tag);

      // Check that it is an Ndef capable card
      if (mNdef!= null) {

      // If we want to read
      // As we did not turn on the NfcAdapter.FLAG_READER_SKIP_NDEF_CHECK
      // We can get the cached Ndef message the system read for us.

      NdefMessage mNdefMessage = mNdef.getCachedNdefMessage();


      // Or if we want to write a Ndef message

      // Create a Ndef Record
      NdefRecord mRecord = NdefRecord.createTextRecord("en","English String");

      // Add to a NdefMessage
      NdefMessage mMsg = new NdefMessage(mRecord);
      
      // Catch errors
      try {
          mNdef.connect();
          mNdef.writeNdefMessage(mMsg);

          // Success if got to here
          runOnUiThread(() -> {
             Toast.makeText(getApplicationContext(),
               "Write to NFC Success",
               Toast.LENGTH_SHORT).show();
          });

          // Make a Sound
          try {
              Uri notification = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
              Ringtone r = RingtoneManager.getRingtone(getApplicationContext(),
                  notification);
              r.play();
              } catch (Exception e) {
                 // Some error playing sound
              }
          
      } catch (FormatException e) {
        // if the NDEF Message to write is malformed
      } catch (TagLostException e) {
        // Tag went out of range before operations were complete
      } catch (IOException e){
        // if there is an I/O failure, or the operation is cancelled
      } finally {
        // Be nice and try and close the tag to
        // Disable I/O operations to the tag from this TagTechnology object, and release resources. 
         try {
                mNdef.close();
             } catch (IOException e) {
               // if there is an I/O failure, or the operation is cancelled
             }
      }

   }

}

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