VM kotlin integration

ChronoActivity2.kt

class ChronoActivity2 : AppCompatActivity() {

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

        // The ViewModelStore provides a new ViewModel or one previously created.
        val chronometerViewModel = getViewModel(this) {
            ChronometerViewModel(SystemClock.elapsedRealtime())
        }

        // Get the chronometer reference
        val chronometer = findViewById<Chronometer>(R.id.chronometer)

        chronometer.base = chronometerViewModel.startTime
        chronometer.start()
    }
}

ChronometerViewModel.kt

class ChronometerViewModel(val startTime: Long) : ViewModel()

ViewModelFactory.kt

class ViewModelFactory<VM : ViewModel>(private val creation: () -> VM) : ViewModelProvider.Factory {

    @Suppress("UNCHECKED_CAST")
    override fun <T : ViewModel> create(modelClass: Class<T>): T = creation() as T
}

inline fun <reified VM : ViewModel> getViewModel(activity: FragmentActivity, key: String? = null, noinline creation: () -> VM): VM {
    return ViewModelProviders
            .of(activity, ViewModelFactory(creation))
            .run {
                if (null == key) {
                    get(VM::class.java)
                } else {
                    get(key, VM::class.java)
                }
            }
}