Change the Top Bar Text

MainActivity.kt

class MainActivity : AppCompatActivity(), Updatable {
    ...

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        //CHANGING THE TEXT OF THE TOP BAR
        val toolbarTitle = findViewById<TextView>(R.id.title)
        val preferences = PreferenceManager.getDefaultSharedPreferences(this)
        var name = preferences.getString("Name", "")
        if (!name.equals("", ignoreCase = true)) {
            toolbarTitle.text = getString(R.string.greeting, name)
        }
    }