TwitterSample search() updated

MainViewModel.kt

class MainViewModel : ViewModel() {
    private val repository = TweetsRepository()
    private val searchWords = MutableLiveData<String>() // trigger

    // tweet data exposed to Views
    val tweetDataResults: LiveData<TweetDataResult> 
        = Transformations.switchMap(searchWords) { str -> repository.loadTweets(str) }

    /**
     * search trigger
     */
    fun search(str: String) {
        Log.d(TAG, "search $str")
        searchWords.value = str
    }
...
}