Single State Pattern

1. StateModel.kt

data class StateModel(
    val detail: ViewResource<Entity1>,
    val something: Entity2?,
    val error: Event<String>?
) {
    companion object {
        val initial = StateModel(
            detail = ViewResource.NotAvailable,
            something = null,
            error = null
        )
    }

2. Event.java

import androidx.annotation.Nullable;

public class Event<T> {
    private T content;
    private boolean hasBeenHandled = false;

    public Event(T content) {
        this.content = content;
    }

    @Nullable
    public T getContentIfNotHandled() {
        if (hasBeenHandled) {
            return null;
        } else {
            hasBeenHandled = true;
            return content;
        }
    }

    public boolean hasBeenHandled() {
        return this.hasBeenHandled;
    }

    @Nullable
    public T peekContent() {
        return content;
    }

    public void ifNotHandled(EventHandler<T> eventHandler) {
        if (!hasBeenHandled) {
            hasBeenHandled = true;
            eventHandler.handle(content);
        }
    }

    public interface EventHandler<T> {
        void handle(T content);
    }
}

3. ViewModel.kt

    private val _state = MutableStateFlow(StateModel.initial)
    val state: StateFlow<StateModel> = _state.asStateFlow()

fun getDetail() {
        _state.value = _state.value.copy(detail = ViewResource.Loading())
        viewModelScope.launch {
            when (val result = repository.getDetail(productId)) {
                is Either.Success ->
                    _state.value = _state.value.copy(detail = ViewResource.Ok(result.value))
                is Either.Failure ->
                    _state.value = _state.value.copy(detail = ViewResource.Error(result.message, result.code))
            }
        }
    }

4. Fragment.kt

viewModel.state.onEach { state ->
    binding.tvName = state.detail.name
    binding.progress.isVisiable = state.detail is ViewResource.Loading
    state.error?.ifNotHandled(::toast)
 }.launchIn(viewLifecycleOwner.lifecycleScope)