Android ViewModel Using SwitchMap

SwitchMapViewModel.kt

class SwitchMapViewModel @Inject constructor(private val dataSource: Data) : ViewModel() {

    // observed by ViewModel as a trigger to retrieve data from the source
    private var liveTrigger: MutableLiveData<String> = MutableLiveData()

    // observed by Activity/Fragment or some other class as a trigger to do something with the data
    private var liveData: LiveData<String>

    init {
        // default observable trigger
        liveTrigger.value = dataSource.defaultText

        // observe liveTrigger and reload observable liveData when trigger changes
        liveData = Transformations.switchMap(liveTrigger) {
            dataSource.fetchData(liveTrigger.value!!)
        }
    }

    // changing liveTrigger's value causes Transformations.switchMap to send a value to the Data
    // model where it's live value is updated. Data model returns it's live data which replaces the
    // ViewModel's live data. MainActivity's observer sees the change and updates it's UI
    // with the new value.
    fun setData(value: String) {
        liveTrigger.value = value
    }

    // retrieve the observable data
    fun getData(): LiveData<String> = liveData
}

SwitchMapViewModelActivity.kt

class SwitchMapViewModelActivity : DaggerAppCompatActivity(), TextInputDialog.OnTextResult {
    @Inject lateinit var data: Data
    @Inject lateinit var factory: ViewModelProvider.Factory

    private val viewModel by lazy(LazyThreadSafetyMode.NONE) {
        ViewModelProviders.of(this, factory).get(SwitchMapViewModel::class.java)
    }

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

        button.setOnClickListener {
            // Custom Dialog Class		
            TextInputDialog(this, R.string.app_name).build().show()
        }

        // Observe the ViewModel's live data. When it changes, update the UI with the new value.
        viewModel.getData().observe(this, Observer {
            it?.let { data -> updateUI:: }
        })
    }

	  // Send the text from the Dialog to the ViewModel.
	  // Transformations.SwitchMap in the ViewModel will notice the change and 
	  // fetch data from the model.
    override fun onTextDialogResult(input: String) {
        viewModel.setData(input)
    }

		// Update the TextView value
    private fun updateUI(data: String) {
        textView.text = data
    }
}