Cannot get Ndef Message from NdefFormatable object

Question

The objective of the readData method below is to return the NDEF message, whether the tag supports the NDEF format or is "NDEF Formatable".

class WritableTag (tag: Tag) {
    private val NDEF = Ndef::class.java.canonicalName
    private val NDEF_FORMATABLE = NdefFormatable::class.java.canonicalName

    private val ndef: Ndef?
    private val ndefFormatable: NdefFormatable?

    val tagId: String?
        get() {
            if (ndef != null) {
                return Tools.byteArrayToHex(ndef.tag.id)
            } else if (ndefFormatable != null) {
                return Tools.byteArrayToHex(ndefFormatable.tag.id)
            }
            return null
        }

    init {
        val technologies = tag.techList
        val tagTechs = Arrays.asList(*technologies)
        if (tagTechs.contains(NDEF)) {
            Log.i("WritableTag", "contains ndef")
            ndef = Ndef.get(tag)
            ndefFormatable = null
        } else if (tagTechs.contains(NDEF_FORMATABLE)) {
            Log.i("WritableTag", "contains ndef_formatable")
            ndefFormatable = NdefFormatable.get(tag)
            ndef = null
        } else {
            throw FormatException("Tag doesn't support ndef")
        }
    }

    fun readData(): NdefMessage {
        if (ndef != null) {
            ndef.connect()
            if (ndef.isConnected) {
                return ndef.ndefMessage
            }
        } else if (ndefFormatable != null) {
            ndefFormatable.connect()
            if (ndefFormatable.isConnected) {
                return ndefFormatable.ndefMessage // Unresolved reference: ndefMessage
            }
        }
        throw Exception("Cannot read ndef message")
    }
}

I can get the ndefMessage from the ndef tag but not from the ndefFormatable tag. How is this possible?

Answer 1

Because a ndefFormatable tag is not in the right state to store ndefMessages, it needs to be formatted to store ndefMessages.

It is not possible to read an ndefMessage from ndefFormatable Tag, it is basically a blank card that is indicating that it could store a ndefMessage if it was setup to store them.

All you can do is format it and then write a ndefMessage