class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        ...

        // todo: singleton?
        val preference = SecurePreferences.create(this@MainActivity)

        binding.btnSave.setOnClickListener {
            val code = binding.etSecretCode.text.toString()
            val msg = binding.etSecretMsg.text.toString()

            preference.saveString(code, msg)
        }

        binding.btnGet.setOnClickListener {
            val code = binding.etCode.text.toString()

            val msg = preference.getString(code)
            if (msg == null) {
                Toast.makeText(
                    this@MainActivity,
                    "No secret message stored with code: $code",
                    Toast.LENGTH_SHORT
                ).show()
            } else {
                binding.tvMsg.text = msg
            }
        }

        binding.btnClear.setOnClickListener {
            preference.clearPreferences()

            Toast.makeText(
                this@MainActivity,
                "All Clear",
                Toast.LENGTH_SHORT
            ).show()
        }
    }
}