kotlin - 如何在 kotlin 中使密封类通用？

Question

是否可以使用下面的 AsyncResult 类来防止在 UserDataAppResult 和 CreateUserResult 中重新定义 InFlight、Error 和 InFlight？

//TODO: use this to make the below classes generic?
sealed class AsyncResult{
  object InFlight : AsyncResult()
  data class Error(val errorMessage: String) : AsyncResult()
  data class Loaded<out T>(val users: T) : AsyncResult()
}

sealed class UserDataAppResult : AppResult() {
  object InFlight : UserDataAppResult()
  data class Error(val errorMessage: String) : UserDataAppResult()
  data class Loaded(val users: List<User>) : UserDataAppResult()
}

sealed class CreateUserResult : AppResult() {
  object InFlight : CreateUserResult()
  data class Error(val errorMessage: String) : CreateUserResult()
  data class Loaded(val users: User) : CreateUserResult()
}

上面的代码有可能是这样的吗？

sealed class AsyncResult{
  class InFlight : AsyncResult()
  data class Error(val errorMessage: String) : AsyncResult()
  data class Loaded<out T>(val users: T) : AsyncResult()
}

sealed class UserDataAppResult : AsyncResult()
sealed class CreateUserResult : AppResult()

val activeUsers: Flowable<UserDataAppResult> = appDatabase.userDao().getActiveUsers(appSettings.currentLanguage.ordinal)
    .map<UserDataAppResult> { UserDataAppResult.Loaded(it) }
    .onErrorReturn { UserDataAppResult.Error(it.localizedMessage) }
    .startWith(UserDataAppResult.InFlight)
    .observeOn(AndroidSchedulers.mainThread())
    .share()

fun createUser(): Flowable<CreateUserResult> {

  val userId = UUID.randomUUID().toString()
  val user = User()
  user.id = userId
  return appDatabase.userDao().insertAll(user)
      .map <CreateUserResult> { CreateUserResult.Loaded(user) }
      .onErrorReturn { CreateUserResult.Error(it.localizedMessage) }
      .startWith(CreateUserResult.InFlight)
}

目前未找到有意义的 UserDataAppResult.Error。但是是否可以重用 AppResult 密封类层次结构并引入新类型。

Answer 1

您的 Object 在 Kotlin 中不能有泛型类型，但这可以通过以下示例解决:

sealed class ResponseState<out T> {
    object Loading : ResponseState<Nothing>()
    data class Error(val throwable: Throwable) : ResponseState<Nothing>()
    data class Success<T>(val item: T) : ResponseState<T>()
}

写作:

val _state = MutableLiveData<ResponseState<MessageModle>>() 


_state.postValue(ResponseState.Loading)

myNetworkCall { response, e
  if (e != null) _state.postValue(ResponseState.Error(e))
  else _state.postValue(ResponseState.Success(response))
}

阅读:

state.observe(..., {state -> 
  when(state) {
    Loading -> showLoading()
    is Error -> showError(state.throwable)
    is Success -> onSuccess(state.item)
  }
}