오류 처리와 사용자 경험

오류 처리가 중요한 이유

UI 상태 모델링

Sealed Class UiState

sealed class UiState<out T> {
    object Loading : UiState<Nothing>()
    data class Success<T>(val data: T) : UiState<T>()
    data class Error(val message: String) : UiState<Nothing>()
}

// In ViewModel:
private val _state = MutableLiveData<UiState<List<Post>>>()
val state: LiveData<UiState<List<Post>>> = _state

fun loadPosts() {
    _state.value = UiState.Loading
    viewModelScope.launch {
        try {
            val posts = withContext(Dispatchers.IO) { repo.getPosts() }
            _state.value = UiState.Success(posts)
        } catch (e: Exception) {
            _state.value = UiState.Error(e.message ?: "Unknown error")
        }
    }
}

UI에서 상태 표시하기

viewModel.state.observe(this) { state ->
    when (state) {
        is UiState.Loading -> {
            binding.progressBar.visibility = View.VISIBLE
            binding.recyclerView.visibility = View.GONE
            binding.tvError.visibility = View.GONE
        }
        is UiState.Success -> {
            binding.progressBar.visibility = View.GONE
            binding.recyclerView.visibility = View.VISIBLE
            adapter.submitList(state.data)
        }
        is UiState.Error -> {
            binding.progressBar.visibility = View.GONE
            binding.tvError.text = state.message
            binding.tvError.visibility = View.VISIBLE
        }
    }
}

Loading에 ProgressBar 사용하기

Snackbar와 Toast 비교

다시 시도 버튼이 있는 Snackbar

import com.google.android.material.snackbar.Snackbar

fun showError(message: String) {
    Snackbar.make(
        binding.root,  // root view of the screen
        message,
        Snackbar.LENGTH_INDEFINITE  // stays until dismissed
    ).setAction("Retry") {
        viewModel.loadPosts()  // retry the request
    }.show()
}

입력값 검증

TextInputLayout 오류

fun validateAndSubmit() {
    val email = binding.etEmail.text.toString().trim()
    val password = binding.etPassword.text.toString()

    var hasError = false

    if (email.isBlank() || !email.contains("@")) {
        binding.tilEmail.error = "Enter a valid email"
        hasError = true
    } else {
        binding.tilEmail.error = null  // clear error
    }

    if (password.length < 6) {
        binding.tilPassword.error = "Minimum 6 characters"
        hasError = true
    } else {
        binding.tilPassword.error = null
    }

    if (!hasError) viewModel.login(email, password)
}

빠른 확인

복습: 오류 처리 및 UX