PagingDataAdapter 정의하기.

PagingDataAdapter는 recyclerAdapter를 확장한다.

 

1. 데이터 로드 상태(LoadState)에 따른 Header/ Footer에 LoadStateAdapter 설정

2. LoadState를 알수 있는 Listener 제공 

3. 아이템 항목을 다시 로드하는 기능 제공

4. 아이템 항목 구분자 설정

5.  DiffUtil.ItemCallback을 지정을 통해 ListAdapter를 사용할때와 같이 사용할 수 있음.

 

private fun initAdapter() {

		// 머릿목록 바닥목록 어뎁터 설정.
        binding.list.adapter = adapter.withLoadStateHeaderAndFooter(
            header = ReposLoadStateAdapter { adapter.retry() },
            footer = ReposLoadStateAdapter { adapter.retry() },
        )
		
        // 로드 상태 리스너 설정
        adapter.addLoadStateListener { loadState ->
        
            // show empty list
            val isListEmpty = loadState.refresh is LoadState.NotLoading && adapter.itemCount == 0
            showEmptyList(isListEmpty)

            // Only show the list if refresh succeeds.
            binding.list.isVisible = loadState.mediator?.refresh is LoadState.NotLoading
            // Show loading spinner during initial load or refresh.
            binding.progressBar.isVisible = loadState.mediator?.refresh is LoadState.Loading
            // Show the retry state if initial load or refresh fails.
            binding.retryButton.isVisible = loadState.mediator?.refresh is LoadState.Error

            // Toast on any error, regardless of whether it came from RemoteMediator or PagingSource
            val errorState =
                loadState.source.append as? LoadState.Error
                    ?: loadState.source.prepend as? LoadState.Error
                    ?: loadState.append as? LoadState.Error
                    ?: loadState.prepend as? LoadState.Error
            errorState?.let {
                Toast.makeText(
                    this,
                    "\uD83D\uDE28 Wooops ${it.error}",
                    Toast.LENGTH_LONG
                ).show()
            }
        }
    }

class ReposAdapter : PagingDataAdapter<UiModel, RecyclerView.ViewHolder>(UI_MODEL_COMPARATOR) {

    companion object {

        private val UI_MODEL_COMPARATOR = object : DiffUtil.ItemCallback<UiModel>() {

            override fun areItemsTheSame(oldItem: UiModel, newItem: UiModel): Boolean =
                (oldItem is UiModel.RepoItem && newItem is UiModel.RepoItem && oldItem.repo.fullName == newItem.repo.fullName)
                        || (oldItem is UiModel.SeparatorItem && newItem is UiModel.SeparatorItem && oldItem.description == newItem.description)

            override fun areContentsTheSame(oldItem: UiModel, newItem: UiModel): Boolean =
                oldItem == newItem
        }
    }

    override fun getItemViewType(position: Int): Int {
        return when (getItem(position)) {
            is UiModel.RepoItem -> R.layout.repo_view_item
            is UiModel.SeparatorItem -> R.layout.separator_view_item
            null -> throw UnsupportedOperationException("Unknown view")
        }
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {

        val uiModel = getItem(position)

        uiModel.let {
            when (uiModel) {
                is UiModel.RepoItem -> (holder as RepoViewHolder).bind(uiModel.repo)
                is UiModel.SeparatorItem -> (holder as SeparatorViewHolder).bind(uiModel.description)
            }
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder =
        if (viewType == R.layout.repo_view_item) {
            RepoViewHolder.create(parent)
        } else {
            SeparatorViewHolder.create(parent)
        }
}