JetPack之Paging3.0

class ArticleAdapter : PagingDataAdapter<Article,ArticleViewHolder>(POST_COMPARATOR){

    companion object{
        val POST_COMPARATOR = object : DiffUtil.ItemCallback<Article>() {
            override fun areContentsTheSame(oldItem: Article, newItem: Article): Boolean =
                    oldItem == newItem

            override fun areItemsTheSame(oldItem: Article, newItem: Article): Boolean =
                    oldItem.id == newItem.id
        }
    }

    override fun onBindViewHolder(holder: ArticleViewHolder, position: Int) {
         holder.tvName.text = getItem(position)?.title
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ArticleViewHolder {
        return ArticleViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.list_item,parent,false))
    }

}
class ArticleViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView){
   val tvName: TextView = itemView.findViewById(R.id.tvname)
}

class ArticleDataSource:PagingSource<Int,Article>() {

    /**
     * 实现这个方法来触发异步加载(例如从数据库或网络)。 这是一个suspend挂起函数，可以很方便的使用协程异步加载
     */
    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Article> {

        return try {
            val page = params.key?:0
            //获取网络数据
            val result = WanRetrofitClient.service.getHomeList(page)
            LoadResult.Page(
                    //需要加载的数据
                    data = result.data.datas,
                    //如果可以往上加载更多就设置该参数，否则不设置
                    prevKey = null,
                    //加载下一页的key 如果传null就说明到底了
                    nextKey = if(result.data.curPage==result.data.pageCount) null else page+1
            )
        }catch (e:Exception){
            LoadResult.Error(e)
        }

    }
}

class ArticleRepository {

    fun getArticleData() = Pager(PagingConfig(pageSize = 20)){
        ArticleDataSource()
    }.flow

}

class PagingViewModel:ViewModel() {

    private val repository:ArticleRepository by lazy { ArticleRepository() }
    /**
     * Pager 分页入口 每个PagingData代表一页数据 最后调用asLiveData将结果转化为一个可监听的LiveData
     */
    fun getArticleData() = repository.getArticleData().asLiveData()

}

class PagingActivity : AppCompatActivity() {

    private val viewModel by lazy { ViewModelProvider(this).get(PagingViewModel::class.java) }

    private val adapter: ArticleAdapter by lazy { ArticleAdapter() }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_paging)

        val refreshView:SmartRefreshLayout = findViewById(R.id.refreshView)
        val recyclerView :RecyclerView = findViewById(R.id.recyclerView)
        recyclerView.layoutManager = LinearLayoutManager(this)
        recyclerView.adapter = adapter.withLoadStateFooter(PostsLoadStateAdapter(adapter))
        //获取数据并渲染UI
        viewModel.getArticleData().observe(this, Observer {
            lifecycleScope.launchWhenCreated {
                adapter.submitData(it)
            }
        })
        //监听刷新状态当刷新完成之后关闭刷新
        lifecycleScope.launchWhenCreated {
            @OptIn(ExperimentalCoroutinesApi::class)
            adapter.loadStateFlow.collectLatest {
                if(it.refresh !is LoadState.Loading){
                    refreshView.finishRefresh()
                }
            }
        }
        refreshView.setOnRefreshListener {
            adapter.refresh()
        }
    }
}

class PostsLoadStateAdapter(
        private val adapter: ArticleAdapter
) : LoadStateAdapter<NetworkStateItemViewHolder>() {
    override fun onBindViewHolder(holder: NetworkStateItemViewHolder, loadState: LoadState) {
        holder.bindTo(loadState)
    }

    override fun onCreateViewHolder(
            parent: ViewGroup,
            loadState: LoadState
    ): NetworkStateItemViewHolder {
        return NetworkStateItemViewHolder(parent) { adapter.retry() }
    }
}

class NetworkStateItemViewHolder(
    parent: ViewGroup,
    private val retryCallback: () -> Unit
) : RecyclerView.ViewHolder(
    LayoutInflater.from(parent.context).inflate(R.layout.network_state_item, parent, false)
) {
    private val progressBar = itemView.findViewById<ProgressBar>(R.id.progress_bar)
    private val errorMsg = itemView.findViewById<TextView>(R.id.error_msg)
    private val retry = itemView.findViewById<Button>(R.id.retry_button)
        .also {
            it.setOnClickListener { retryCallback() }
        }

    fun bindTo(loadState: LoadState) {
        progressBar.isVisible = loadState is Loading
        retry.isVisible = loadState is Error
        errorMsg.isVisible = !(loadState as? Error)?.error?.message.isNullOrBlank()
        errorMsg.text = (loadState as? Error)?.error?.message
    }
}

recyclerView.adapter = adapter.withLoadStateFooter(PostsLoadStateAdapter(adapter))