Jetpack之分页组件 - Paging

配置

implementation "androidx.paging:paging-runtime-ktx:2.1.2"

基本使用

构建数据源

自定义DataSource.Factory<Key, Value>：

class UserDataSourceFactory : DataSource.Factory<Int, User>() {
    val sourceLiveData = MutableLiveData<UserDataSource3>()

    override fun create(): DataSource<Int, User> {
        val latestSource = UserDataSource3()
        sourceLiveData.postValue(latestSource)
        return latestSource
    }
}

// 自定义数据源，可根据实际使用场景选择要实现的数据源(ItemKeyedDataSource/PositionalDataSource/PageKeyedDataSource)
class UserDataSource3 : PageKeyedDataSource<Int, User>() {

    // 下拉刷新状态
    val refreshState = MutableLiveData<Boolean>()

    override fun loadInitial(
        params: LoadInitialParams<Int>,
        callback: LoadInitialCallback<Int, User>
    ) {
        refreshState.postValue(true)
        val items = fetchItems(
            1,
            params.requestedLoadSize
        )
        Log.d("test", "loadInitial")
        callback.onResult(items, null, 2)
        refreshState.postValue(false)
    }

    override fun loadBefore(params: LoadParams<Int>, callback: LoadCallback<Int, User>) {
    }

    override fun loadAfter(params: LoadParams<Int>, callback: LoadCallback<Int, User>) {
        val items = fetchItems(
            params.key,
            params.requestedLoadSize
        )
        Log.d("test", "loadAfter")
        callback.onResult(items, params.key + 1)
    }

    private fun fetchItems(key: Int?, requestedLoadSize: Int): ArrayList<User> {
        val index = key ?: 1
        val start = (index - 1) * requestedLoadSize
        val end = start + requestedLoadSize - 1
        val users = ArrayList<User>()
        for (i in start..end) {
            users.add(User(i, "name$i"))
        }

        Thread.sleep(500)

        return users
    }

}

关联数据

在ViewModel中使用LivePagedListBuilder关联数据:

// 自定义数据源工厂(也可以配合Room组件使用)
private val factory = UserDataSourceFactory()

// 分页配置
private val config = PagedList.Config.Builder()
    .setPageSize(10) // 每页大小
    .setEnablePlaceholders(false) // 是否启用占位符
    .setInitialLoadSizeHint(10) // 初始加载数目
    .setPrefetchDistance(2) // 自动开启预加载间距数目
    .build()

val users: LiveData<PagedList<User>> = LivePagedListBuilder(factory, config).build()

构建adapter

实现自定义PagedListAdapter：

class UserListAdapter : PagedListAdapter<User, UserListAdapter.UserViewHolder>(DIFF_CALLBACK) {

    companion object {
        // 比对接口
        private 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 onCreateViewHolder(parent: ViewGroup, viewType: Int) = UserViewHolder(parent)

    override fun onBindViewHolder(holder: UserViewHolder, position: Int) =
        holder.bindData(getItem(position))

    class UserViewHolder(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 bindData(item: User?) {
            tvName.text = item?.name
        }
    }
}

展示数据

在界面中监听数据变化，显示数据：
```
vm.users.observe(this) {
    adapter.submitList(it)
}
```

如此就完成基于RecyclerView的数据自动分页加载逻辑。

参考

paging

DarklyCoder/Paging2Demo

Jetpack之分页组件 - Paging

配置

基本使用

参考