Clearlove2015 / Paging3Demo

Android Jetpack分页库demo

Jetpack分页加载库-Paging

配置

implementation "androidx.paging:paging-runtime:3.0.0-alpha05"

基本使用

1. 自定义数据源

   自定义实现PagingSource:

   class UserPagingSource : PagingSource<Int, User>() {
   
       override suspend fun load(params: LoadParams<Int>): LoadResult<Int, User> {
           try {
               val page = params.key ?: 1
               // 获取分页数据
               val response = fetchData(page, params.loadSize)
   
               // 获取正确结果
               return LoadResult.Page(
                   data = response,
                   prevKey = if (page == 1) null else page,
                   nextKey = page + 1
               )
   
           } catch (e: Exception) {
               // 处理错误
               return LoadResult.Error(e)
           }
       }
   
       private fun fetchData(page: Int, size: Int): List<User> {
           val start = (page - 1) * size
           val end = start + size - 1
           val users = ArrayList<User>()
           for (i in start..end) {
               users.add(User(i, "name$i"))
           }
   
           Thread.sleep(500)
   
           return users
       }
   
   }

2. 连接数据源

   在ViewModel通过Pager连接数据源

   private val config = PagingConfig(
       pageSize = 10,
       prefetchDistance = 2,
       initialLoadSize = 10
   )
   
   val flow = Pager(config = config) { UserPagingSource() }.flow.cachedIn(viewModelScope)

3. 创建Adapter

   继承PagingDataAdapter<T,VH>实现adapter:

   class UserAdapter : PagingDataAdapter<User, UserAdapter.VH>(DIFF_CALLBACK) {
   
       companion object {
           val DIFF_CALLBACK = object : DiffUtil.ItemCallback<User>() {
               override fun areItemsTheSame(oldItem: User, newItem: User) = oldItem.uid == newItem.uid
               override fun areContentsTheSame(oldItem: User, newItem: User) = oldItem == newItem
           }
       }
   
       override fun onBindViewHolder(holder: VH, position: Int) = holder.bind(getItem(position))
   
       override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) = VH(parent)
   
       class VH(parent: ViewGroup) : RecyclerView.ViewHolder(
           LayoutInflater.from(parent.context).inflate(R.layout.user_item, parent, false)
       ) {
   
           private val tvName = itemView.findViewById<TextView>(R.id.tv_name)
   
           fun bind(item: User?) {
               tvName.text = item?.name
           }
       }
   
   }

4. 展示数据

    private val vm by viewModels<UserViewModel>()
    ......
    // 在Activities下可以直接使用`lifecycleScope`, 但在`Fragments`里使用`viewLifecycleOwner.lifecycleScope`
    lifecycleScope.launch {
        vm.flow.collectLatest { adapter.submitData(it) }
    }

如上即可完成正常的分页显示。

进阶使用

显示加载状态

框架对外暴露了分页数据的加载状态，通过LoadState对象展示当前状态：

• LoadState.NotLoading: 没有发生操作和错误
• LoadState.Loading: 加载操作中
• LoadState.Error: 发生了错误

1. 通过添加listener监听状态：

   通过 PagingDataAdapter 的 addLoadStateListener方法监听

    lifecycleScope.launch {
       // 监听加载状态
       adapter.loadStateFlow.collectLatest {
           Log.d("test", it.refresh.toString())
       }
    }

2. 通过adapter展示加载状态

   class LoadStateViewHolder(parent: ViewGroup, retry: () -> Unit) : RecyclerView.ViewHolder(
     LayoutInflater.from(parent.context) .inflate(R.layout.load_state_item, parent, false)
   ) {
     private val binding = LoadStateItemBinding.bind(itemView)
     private val progressBar: ProgressBar = binding.progressBar
     private val errorMsg: TextView = binding.errorMsg
     private val retry: Button = binding.retryButton
       .also {
         it.setOnClickListener { retry() }
       }
   
     fun bind(loadState: LoadState) {
       if (loadState is LoadState.Error) {
         errorMsg.text = loadState.error.localizedMessage
       }
   
       progressBar.isVisible = loadState is LoadState.Loading
       retry.isVisible = loadState is LoadState.Error
       errorMsg.isVisible = loadState is LoadState.Error
     }
   }
   
   // 继承LoadStateAdapter
   class ExampleLoadStateAdapter(private val retry: () -> Unit) : LoadStateAdapter<LoadStateViewHolder()> {
   
     override fun onCreateViewHolder(parent: ViewGroup,loadState: LoadState ) = LoadStateViewHolder(parent, retry)
   
     override fun onBindViewHolder(holder: LoadStateViewHolder,loadState: LoadState) = holder.bind(loadState)
   }

   // 使用adapter替换recycleview绑定的adapter
   // 也可使用`withLoadStateHeader()` / `withLoadStateFooter()` 显示header/footer
   val adapter = pagingAdapter
     .withLoadStateHeaderAndFooter(
       header = ExampleLoadStateAdapter(adapter::retry),
       footer = ExampleLoadStateAdapter(adapter::retry)
     )

RemoteMediator

TODO

参考

1. Paging3
2. PagingConfig