Google Android - это несложно

Код: Выделить всё

class MainActivity : AppCompatActivity() {

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

    val liveData = DataController.getData()

    liveData?.observe(this, Observer<String>() {
        @Override
        fun onChanged(@Nullable value:String) {
            textView.text = value
        }
    });
}

fun refresh(view: View) {
    DataController.refresh()
}

object DataController {                                 //  это синглтон!
private val liveData = MutableLiveData<String>()

fun getData(): LiveData<String>? {
    return liveData
}

fun getCurrentDateTime(): Date {
    return Calendar.getInstance().time
}

fun refresh(){
    val date = getCurrentDateTime()
    val dateInString = date.toString()
    liveData.value = dateInString
}