Android(安卓)Paging组件Demo

Android Paging组件的作用

Android官方的分页加载组件，可以RecyclerView上实现在数据分页加载，无限滚动的效果。官方例子：https://github.com/googlesamples/android-architecture-components/tree/master/PagingWithNetworkSample

需要添加的依赖

implementation "com.android.support:appcompat-v7:28.0.0"implementation "com.android.support:recyclerview-v7:28.0.0"implementation "com.android.support:swiperefreshlayout:28.0.0"implementation "android.arch.paging:runtime:1.0.1"implementation "android.arch.lifecycle:extensions:1.1.1"//使用Androidx的依赖//implementation "androidx.appcompat:appcompat:1.0.2"//implementation "androidx.recyclerview:recyclerview:1.0.0"//implementation "androidx.swiperefreshlayout:swiperefreshlayout:1.0.0"//implementation "androidx.paging:paging-runtime:2.0.0"//implementation "androidx.lifecycle:lifecycle-extensions:2.0.0"

主要用到这几个类

PagedListAdapter：RecyclerView使用的适配器

DataSource：数据源，常用的子类ItemKeyedDataSource、PageKeyedDataSource

LivePagedListBuilder：实现对象需要传入数据源工厂和请求的页面长度

ItemKeyedDataSource

一般使用id或位置标识加载数据

class DataSourceByItem: ItemKeyedDataSource() {    override fun loadInitial(params: LoadInitialParams, callback: LoadInitialCallback) {        //初始化加载数据        params.requestedInitialKey//初始化key        params.requestedLoadSize//请求数据的长度        callback.onResult(ArrayList())//回调结果    }    override fun loadAfter(params: LoadParams, callback: LoadCallback) {        //获取下一页的数据        params.key//通过getKey()获取RecyclerView最后一个key        params.requestedLoadSize//请求数据的长度        callback.onResult(ArrayList())//回调结果    }    override fun loadBefore(params: LoadParams, callback: LoadCallback) {        //获取上一页的数据        params.key//通过getKey()获取RecyclerView第一个key        params.requestedLoadSize//请求数据的长度        callback.onResult(ArrayList())//回调结果    }    override fun getKey(item: DataBean): Int {        //获取id（位置标识）        return item.id    }}

PageKeyedDataSource

一般使用页码加载

class DataSourceByPage : PageKeyedDataSource() {    override fun loadInitial(params: LoadInitialParams, callback: LoadInitialCallback) {        //初始化加载数据        params.requestedLoadSize//请求数据的长度        callback.onResult(ArrayList(),/*上一页的页码*/0,/*下一页的页面*/2)//回调结果    }    override fun loadAfter(params: LoadParams, callback: LoadCallback) {        //获取下一页的数据        params.key//需要请求页面的页码        params.requestedLoadSize//请求数据的长度        callback.onResult(ArrayList(),/*下一页的页码*/params.key + 1)//回调结果    }    override fun loadBefore(params: LoadParams, callback: LoadCallback) {        //获取上一页的数据        params.key//需要请求页面的页码        params.requestedLoadSize//请求数据的长度        callback.onResult(ArrayList(), /*上一页的页码*/params.key - 1)//回调结果    }}

LivePagedListBuilder

private val dataSourceFactory = object : DataSource.Factory() {    override fun create(): DataSource {        return DataSourceByItem()//初始化创建数据源对象，加载上一页或下一页不会创建    }}private val config = PagedList.Config.Builder()    .setInitialLoadSizeHint(60)//初始化请求数据的长度（就是DataSource.loadInitial方法中的params.requestedLoadSize）    .setPageSize(30)//请求数据的长度（loadAfter和loadBefore方法）    .build()private val livePagedList = LivePagedListBuilder(dataSourceFactory, config).build()

PagedListAdapter

class ListAdapter : PagedListAdapter(comparator) {    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {    }    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {    }    companion object {        private val comparator = object : DiffUtil.ItemCallback() {            override fun areItemsTheSame(oldItem: DataBean, newItem: DataBean): Boolean {                //比较唯一id                return oldItem.id == newItem.id            }            override fun areContentsTheSame(oldItem: DataBean, newItem: DataBean): Boolean {                //比较包含对象                return oldItem == newItem            }        }    }}

Demo

使用SwipeRefreshLayout和RecyclerView实现下拉刷新和分页加载

定义加载状态

enum class LoadingState {    Normal, //    Loading, //加载中    Failed, //出错，重试    NotMore,//没有更多数据    Empty//空视图}

数据实体类

class DataBean  {    var id = 0    var string = "string"}

Activity布局文件

activity

class MainActivity : AppCompatActivity() {    private val viewModel by lazy { ViewModelProviders.of(this)[ListViewModel::class.java] }    private val adapter = ListAdapter { viewModel.retry() }    override fun onCreate(savedInstanceState: Bundle?) {        super.onCreate(savedInstanceState)        setContentView(R.layout.activity_main)        recyclerView.adapter = adapter        viewModel.result.observe(this, Observer {            it?.let { result ->                if (result.isInit) {                    if (result.loadingState == LoadingState.Empty) {                        //初始化加载数据为空，设置recyclerView空视图                        recyclerView.post { adapter.setEmptyView() }                    }                    //更新下拉刷新的状态                    swipeRefreshLayout.post {                        swipeRefreshLayout.isRefreshing = (result.loadingState == LoadingState.Loading)                    }                } else {                    recyclerView.post { adapter.setLoadingState(result.loadingState) }                }            }        })        viewModel.livePagedList.observe(this, Observer {            //初始化时，添加数据到适配器            adapter.submitList(it)        })        swipeRefreshLayout.setOnRefreshListener {            //下拉刷新            viewModel.refresh()        }    }}

class ListAdapter(private val retryCallback: () -> Unit) : PagedListAdapter(comparator) {    private var listState = LoadingState.Normal    private fun isShowLastRow(): Boolean {        //是否显示加载视图        return when (listState) {            LoadingState.Loading, LoadingState.Failed, LoadingState.NotMore -> true            else -> false        }    }    private fun isShowEmptyView(): Boolean {        //是否显示空视图        return super.getItemCount() == 0 && listState == LoadingState.Empty    }    override fun getItemCount(): Int {        return super.getItemCount() +                if (isShowLastRow() || isShowEmptyView()) {                    1                } else {                    0                }    }    override fun getItemViewType(position: Int): Int {        return if (isShowLastRow() && position == itemCount - 1) {            R.layout.list_item_loading        } else if (isShowEmptyView()) {            R.layout.list_item_empty        } else {            R.layout.list_item        }    }    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {        val view = LayoutInflater.from(parent.context).inflate(viewType, parent, false)        return when (viewType) {            R.layout.list_item -> ItemViewHolder(view)            R.layout.list_item_loading -> LoadingViewHolder(view, retryCallback) { listState }            else -> object : RecyclerView.ViewHolder(view) {}        }    }    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {        when (getItemViewType(position)) {            R.layout.list_item -> getItem(position)?.let { (holder as ItemViewHolder).updateView(it) }            R.layout.list_item_loading -> (holder as LoadingViewHolder).updateView()        }    }    fun setLoadingState(loadingState: LoadingState) {        //更新分页加载状态        if (this.listState == loadingState)            return        val lastItemCount = itemCount        this.listState = loadingState        if (itemCount - 1 == lastItemCount) {            notifyItemInserted(lastItemCount - 1)        } else if (itemCount + 1 == lastItemCount) {            notifyItemRemoved(lastItemCount - 1)        } else if (itemCount == lastItemCount) {            notifyItemChanged(lastItemCount - 1)        }//        notifyItemChanged(lastItemCount - 1)    }    fun setEmptyView() {        //显示空数据视图        if (this.listState == LoadingState.Empty)            return        this.listState = LoadingState.Empty        notifyDataSetChanged()    }    companion object {        private val comparator = object : DiffUtil.ItemCallback() {            override fun areItemsTheSame(oldItem: DataBean, newItem: DataBean) = (oldItem.id == newItem.id)            override fun areContentsTheSame(oldItem: DataBean, newItem: DataBean) = (oldItem == newItem)        }    }}

class ListViewModel : ViewModel() {    private val pageSize = 30    private val config = PagedList.Config.Builder()        .setInitialLoadSizeHint(pageSize * 2)        .setPageSize(pageSize)        .build()    private val dataSource = MutableLiveData()    val result = switchMap(dataSource) { it.getResultBean() }!!    private val dataSourceFactory = object : DataSource.Factory() {        override fun create(): DataSource {            //初始化创建数据源对象，加载上一页或下一页不会创建            return DataSourceByItem().apply { dataSource.postValue(this) }        }    }    val livePagedList = LivePagedListBuilder(dataSourceFactory, config).build()    fun refresh() {        //刷新页面        dataSource.value?.refresh()    }    fun retry() {        //重试        dataSource.value?.retry()    }}

class DataSourceByItem : ItemKeyedDataSource(), IDataSource {    val result = MutableLiveData()    private var retry: (() -> Unit)? = null    override fun loadInitial(params: LoadInitialParams, callback: LoadInitialCallback) {        result.postValue(ResultBean(true, LoadingState.Loading))        var isReturn = 0        //异步请求远程数据        RemoteData.getById(0, params.requestedLoadSize) { isSuccess, list ->            if (isSuccess) {                result.postValue(ResultBean(true, if (list.isEmpty()) LoadingState.Empty else LoadingState.Normal))                callback.onResult(list)            } else {                result.postValue(ResultBean(true, LoadingState.Failed))                retry = {                    loadInitial(params, callback)                }            }            isReturn = 1        }        //等待请求完成        while (isReturn == 0) {            Thread.sleep(100)        }    }    override fun loadAfter(params: LoadParams, callback: LoadCallback) {        result.postValue(ResultBean(false, LoadingState.Loading))        RemoteData.getById(params.key, params.requestedLoadSize) { isSuccess, list ->            if (isSuccess) {                result.postValue(ResultBean(false, if (list.isEmpty()) LoadingState.NotMore else LoadingState.Normal))                callback.onResult(list)            } else {                result.postValue(ResultBean(false, LoadingState.Failed))                retry = {                    loadAfter(params, callback)                }            }        }    }    override fun loadBefore(params: LoadParams, callback: LoadCallback) {    }    override fun getKey(item: DataBean): Int {        return item.id    }    override fun retry() {        retry?.let {            //重试请求            retry = null            it()        }    }    override fun refresh() {        //初始化刷新        invalidate()    }    override fun getResultBean(): MutableLiveData {        return result    }}

模拟请求远程数据

object RemoteData {    private var errorCount = 0    fun getById(id: Int, size: Int, callback: (isSuccess: Boolean, list: ArrayList) -> Unit) {        //获取大于id的size条记录，当id大于100模拟一次错误请求，当id大于200返回空记录        Thread {            log("id:$id,size:$size")            val list = arrayListOf()            val start = id + 1            val end = id + size            for (i in start..end) {                list.add(DataBean().apply {                    this.id = i                    this.string = "item$i"                })            }            val isSuccess = if (id < 100) {                errorCount = 1                true            } else {                --errorCount < 0            }            Thread.sleep(2000)            callback(isSuccess, if (id > 200) arrayListOf() else list)        }.start()    }}

完整的项目：https://github.com/dingjianlun/PagingDemo