Write Nfc Data On An Tag With Android Studio

I'm creating an application in which I have to write a series of values that come to me from a file to an NFC card and I've been reading and I don't know where to really start, I h

Solution 1:

The first place I would start is thinking about how to store the data.

Is the data custom to your application or do you want to share it with other App's?

Will the App be just writing the data once or will it be updating it (wanting to Append Data to existing data stored on the card?

Update: from your comments about the data type you are probably better using the higher level NDEF format to store your Data using a custom mime type. This is assuming your chosen card type supports this. Note the example I gave is reading/writing using low level commands read and writing page by page.

How many bytes of data do you want to store (Influences the card technology)

You probably want to also think about what NFC card technology you want to use, probably a good choice of one of the NTAG 21x series of cards.

What is the minimum version of Android you want to target?

I would not use the newIntent method as this is very unreliable for writing data, I would use the enableReaderMode if you are targeting a high enough version of Android.

https://developer.android.com/reference/android/nfc/NfcAdapter.html#enableReaderMode(android.app.Activity,%20android.nfc.NfcAdapter.ReaderCallback,%20int,%20android.os.Bundle)

Some of the answers to what you need to think about will affect some of the details of the example.

Update: based on comments Even though you are using Fragments I would still put the mechanics of NFC handling in the Activity.

The reason for this is because the OS is still handling tag discovery, if you don't "claim" the NFC hardware in every Fragment then it is possible especially with the NDEF data format, for the OS to display a screen over your App if the user present a card at the wrong time, giving a bad user experience.

In my multi Activity App I "claim" the NFC hardware in every Activity even if a lot of them do "On Tag discovered, do nothing" because they are not the NFC Activity.

So unless you want to write the same code in every Fragment, it would be much better to call the NFC stuff from your one Activity and then in onTagDiscovered does something like (pseudo code):-

Updated:

if displaying the NFC user prompt Fragment.
get data to file.
write data to the card.
Notify user that it is done.
elsedonothingwhen other fragments are displayed.

or you could have card writing at any time the App is open (again best done in activity not in any fragment)

If card is presented no matter what fragment is being display
getdata from the file
write data to the card
Notify user that it is done.

Sorry I cannot do an example in Kotlin but here is a barebone of a Java Example, extracted from my App (not tested, so there could be copy and pasted errors)

publicclassMainActivityextendsAppCompatActivityimplementsNfcAdapter.ReaderCallback{

private NfcAdapter mNfcAdapter;

@OverrideprotectedvoidonCreate(Bundle savedInstanceState) {
    // All normal onCreate Stuff// Listen to NFC setting changesthis.registerReceiver(mReceiver, filter);
    }

    // Listen for NFC being turned on while in the AppprivatefinalBroadcastReceivermReceiver=newBroadcastReceiver() {
        @OverridepublicvoidonReceive(Context context, Intent intent) {
            finalStringaction= intent.getAction();

            if (action.equals(NfcAdapter.ACTION_ADAPTER_STATE_CHANGED)) {
                finalintstate= intent.getIntExtra(NfcAdapter.EXTRA_ADAPTER_STATE,
                        NfcAdapter.STATE_OFF);
                switch (state) {
                    case NfcAdapter.STATE_OFF:
                    // Tell the user to turn NFC on if App requires itbreak;
                    case NfcAdapter.STATE_TURNING_OFF:
                        break;
                    case NfcAdapter.STATE_ON:
                        enableNfc();
                        break;
                    case NfcAdapter.STATE_TURNING_ON:
                        break;
                }
            }
        }
    };

    @OverrideprotectedvoidonResume() {
        super.onResume();

        enableNfc();

    }

    @OverrideprotectedvoidonPause() {
        super.onPause();
        if(mNfcAdapter!= null)
            mNfcAdapter.disableReaderMode(this);
    }




    privatevoidenableNfc(){
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

        if(mNfcAdapter!= null && mNfcAdapter.isEnabled()) {

            // Work around some buggy hardware that checks for cards too fastBundleoptions=newBundle();
            options.putInt(NfcAdapter.EXTRA_READER_PRESENCE_CHECK_DELAY, 1000);


            // Listen for all types of card when this App is in the foreground// Turn platform sounds off as they misdirect users when writing to the card// Turn of the platform decoding any NDEF data
            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_SKIP_NDEF_CHECK |
                            NfcAdapter.FLAG_READER_NO_PLATFORM_SOUNDS,
                    options);
        } else {
            // Tell the user to turn NFC on if App requires it
        }
    }

    publicvoidonTagDiscovered(Tag tag) {

        // This is run in a separate Thread to UIStringBuilderUid=newStringBuilder();

        booleansuccessUid= getUID(tag, Uid);
        if (!successUid){
            // Not a successful readreturn;
        } else {
            // Feedback to user about successful readVibratorv= (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
            v.vibrate(500);
            runOnUiThread(newRunnable() {
                @Overridepublicvoidrun() {
                    // Update the UI / notify user  
                }
            });
            // Finish Tasktry {
                Urinotification= RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
                Ringtoner= RingtoneManager.getRingtone(getApplicationContext(), notification);
                r.play();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    publicbooleangetUID(Tag tag, StringBuilder Uid){
        NfcAmNfcA= NfcA.get(tag);

        if (mNfcA != null) {
            // The tag is NfcA capabletry {
                mNfcA.connect();
                // Do a Read operation at page 0 an 1byte[] result = mNfcA.transceive(newbyte[] {
                        (byte)0x3A,  // FAST_READ
                        (byte)(0 & 0x0ff),
                        (byte)(1 & 0x0ff),
                });

                if (result == null) {
                    // either communication to the tag was lost or a NACK was received// Log and returnreturnfalse;
                } elseif ((result.length == 1) && ((result[0] & 0x00A) != 0x00A)) {
                    // NACK response according to Digital Protocol/T2TOP// Log and returnreturnfalse;
                } else {
                    // success: response contains ACK or actual datafor (inti=0; i < result.length; i++) {
                        // byte 4 is a check byteif (i == 3) continue;
                        Uid.append(String.format("%02X ", result[i]));
                    }

                    // Close and returntry {
                        mNfcA.close();
                    } catch (IOException e) {
                    }
                    returntrue;
                }

            } catch (TagLostException e) {
                // Log and returnreturnfalse;
            } catch (IOException e){
                // Log and returnreturnfalse;
            } finally {
                try {
                    mNfcA.close();
                } catch (IOException e) {
                }
            }
        } else {
            // Log errorreturnfalse;
        }
    }

}