Exemplo de query com edittext e lista

CityCodeAdapter.kt

class CityCodeAdapter: BaseAdapter {
  val list = MutableList()
  
  // Outros métodos obrigatórios do adapter
  
  fun updateList(cityList: MutableList<CityCode>) {
        this.list.clear()
        this.list.addAll(cityList)
        notifyDataSetChanged()
    }
}

SearchActivity.kt

class SearchCityActivity : BaseActivity() {

    private lateinit var cityAdapter: CityCodeAdapter
    private val cityList: MutableList<CityCode> = ArrayList()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_search_city)
      
      // instancia o adapter
      cityAdapter = CityCodeAdapter(/* inicio o adapter */)
      
      // passa o adapter pra listview ou recyclerview
      
      // instancia o listener do edittext
      searchText.setOnEditorActionListener({ textview, actionId, event ->
            if (actionId == EditorInfo.IME_ACTION_SEARCH) {
                searchCities(textview.text.toString())
                true
            } else {
                false
            }
        })
    }
  
  private fun searchCities(query: String?): Boolean {
        if (!query.isNullOrBlank()) {
          // faz uma consulta no banco e pega a nova lista
          val listaNova = DB.queryListCity()
          // seta a lista nova no adapter
          cityAdapter.updateList(listaNova.toMutableList()) // toMutableList é um método do kotlin, não precisa usar ele.
        }
        return true
    }
  
}