按页显示内容(Android/Kotlin)

dependencies {
    implementation "com.squareup.retrofit2:retrofit:2.9.0"
    implementation "com.squareup.retrofit2:converter-gson:2.9.0"
    implementation "androidx.paging:paging-runtime-ktx:3.0.0"
}

data class Item(val id: Int, val name: String)

interface ApiService {
    @GET("items")
    suspend fun getItems(@Query("page") page: Int, @Query("limit") limit: Int): List<Item>
}

class ItemPagingSource(private val apiService: ApiService) : PagingSource<Int, Item>() {
    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Item> {
        return try {
            val page = params.key ?: 1
            val response = apiService.getItems(page, params.loadSize)
            LoadResult.Page(
                data = response,
                prevKey = if (page == 1) null else page - 1,
                nextKey = if (response.isEmpty()) null else page + 1
            )
        } catch (e: Exception) {
            LoadResult.Error(e)
        }
    }

    override fun getRefreshKey(state: PagingState<Int, Item>): Int? {
        return state.anchorPosition?.let { anchorPosition ->
            state.closestPageToPosition(anchorPosition)?.prevKey?.plus(1)
                ?: state.closestPageToPosition(anchorPosition)?.nextKey?.minus(1)
        }
    }
}

class ItemAdapter : PagingDataAdapter<Item, ItemViewHolder>(ItemDiffCallback()) {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ItemViewHolder {
        val inflater = LayoutInflater.from(parent.context)
        val binding = ItemBinding.inflate(inflater, parent, false)
        return ItemViewHolder(binding)
    }

    override fun onBindViewHolder(holder: ItemViewHolder, position: Int) {
        val item = getItem(position)
        item?.let { holder.bind(it) }
    }
}

class ItemViewHolder(private val binding: ItemBinding) : RecyclerView.ViewHolder(binding.root) {
    fun bind(item: Item) {
        binding.name.text = item.name
    }
}

class ItemDiffCallback : DiffUtil.ItemCallback<Item>() {
    override fun areItemsTheSame(oldItem: Item, newItem: Item): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areContentsTheSame(oldItem: Item, newItem: Item): Boolean {
        return oldItem == newItem
    }
}

class ItemViewModel(private val apiService: ApiService) : ViewModel() {
    val items = Pager(PagingConfig(pageSize = 20)) {
        ItemPagingSource(apiService)
    }.flow.cachedIn(viewModelScope)
}

class ItemListFragment : Fragment() {
    private lateinit var viewModel: ItemViewModel
    private lateinit var adapter: ItemAdapter

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val binding = FragmentItemListBinding.inflate(inflater, container, false)
        viewModel = ViewModelProvider(this).get(ItemViewModel::class.java)
        adapter = ItemAdapter()
        binding.recyclerView.adapter = adapter
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        viewModel.items.collectLatest { pagingData ->
            adapter.submitData(pagingData)
        }
    }
}