• Paging 实现加载更多

    1. 基于 保存图片到相册 修改添加

    保存图片到相册https://blog.csdn.net/u011193452/article/details/127065427

    2. 新增引用库

    1. dependencies {
    2.     def paging_version = "3.1.1"
    3.     implementation "androidx.paging:paging-runtime:$paging_version"
    4.     // alternatively - without Android dependencies for tests
    5.     testImplementation "androidx.paging:paging-common:$paging_version"
    6.  
    7.     //retrofit网络请求库
    8.     implementation 'com.squareup.retrofit2:retrofit:2.9.0'
    9.     implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
    10. }

    3. 第一种方式，使用 Paging2， API 已过时

      3.1 实现 PageKeyedDataSource 文件 PixabayDataSources.kt

    1. class PixabayDataSources(private val context: Context) : PageKeyedDataSource<Int, PhotoItem>() {
    2.     private val queryKey =
    3.         arrayOf("cat", "beauty", "car", "dog", "phone", "computer", "flower", "animal")
    4.     private var keyValue = ""
    5.     //Initial 最初
    6.     override fun loadInitial(
    7.         params: LoadInitialParams<Int>, callback: LoadInitialCallback<Int, PhotoItem>
    8.     ) {
    9.         keyValue = queryKey.random()
    10.         val url = "https://pixabay.com/api/?key=30070990-cfc31c9f778ceeef4009d910d&q=${keyValue}&per_page=30&page=1"
    11.         StringRequest(
    12.             Request.Method.GET,
    13.             url,
    14.             {
    15.                 val dataList = Gson().fromJson(it, Pixabay::class.java).hits.toList()
    16.                 callback.onResult(dataList, null, 2)
    17.             },
    18.             {
    19.                 Log.e("MyTag", "loadInitial: $it")
    20.             }
    21.         ).also {
    22.              VolleySingleton.getInstance(context).requestQueue.add(it)
    23.         }
    24.     }
    25.  
    26.     override fun loadAfter(params: LoadParams<Int>, callback: LoadCallback<Int, PhotoItem>) {
    27.         val url =
    28.             "https://pixabay.com/api/?key=30070990-cfc31c9f778ceeef4009d910d&q=${keyValue}&per_page=30&page=${params.key}"
    29.         StringRequest(
    30.             Request.Method.GET,
    31.             url,
    32.             {
    33.                 val dataList = Gson().fromJson(it, Pixabay::class.java).hits.toList()
    34.                 callback.onResult(dataList, params.key + 1)
    35.             },
    36.             {
    37.                 Log.e("MyTag", "loadAfter: $it")
    38.             }
    39.         ).also {
    40.             VolleySingleton.getInstance(context).requestQueue.add(it)
    41.         }
    42.     }
    43.  
    44.     override fun loadBefore(params: LoadParams<Int>, callback: LoadCallback<Int, PhotoItem>) {
    45.     }
    46. }

      3.2 实现 DataSource.Factory, PixabayDataSourceFactory.kt

    1. class PixabayDataSourceFactory(private val context: Context) : DataSource.Factory<Int, PhotoItem>() {
    2.     override fun create(): DataSource<Int, PhotoItem> {
    3.         return PixabayDataSources(context)
    4.     }
    5. }

      3.4 修改 ViewModel， GalleryViewModel.kt

    1. class GalleryViewModel(application: Application) : AndroidViewModel(application) {
    2.     val pagedListLiveData = PixabayDataSourceFactory(application).toLiveData(1)
    3.     fun resetQuery() {
    4.        pagedListLiveData.value?.dataSource?.invalidate()
    5.     }
    6. }

      3.5 修改继承 ListAdapter 为 PagedListAdapter，修改判空

      3.6 调用 GalleryFragment.kt

    1. class GalleryFragment : Fragment() {
    2.     private lateinit var binding: FragmentGalleryBinding
    3.     private lateinit var galleryAdapter:GalleryAdapter
    4.     private val galleryViewModel by viewModels()
    5.  
    6.     override fun onCreateView(
    7.         inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    8.     ): View? {
    9.         binding = FragmentGalleryBinding.inflate(inflater, container, false)
    10.         return binding.root
    11.     }
    12.  
    13.     override fun onOptionsItemSelected(item: MenuItem): Boolean {
    14.         when (item.itemId) {
    15.             R.id.swipeIndicator -> {
    16.                 binding.swipeLayoutGallery.isRefreshing = true
    17.                 Handler().postDelayed({
    18.                     galleryViewModel.resetQuery()
    19.                 }, 300)
    20.  
    21.             }
    22.         }
    23.         return super.onOptionsItemSelected(item)
    24.     }
    25.  
    26.     //加载菜单栏
    27.     override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
    28.         super.onCreateOptionsMenu(menu, inflater)
    29.         inflater.inflate(R.menu.menu, menu)
    30.     }
    31.  
    32.     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    33.         super.onViewCreated(view, savedInstanceState)
    34.         setHasOptionsMenu(true)
    35.         galleryAdapter = GalleryAdapter()
    36.  
    37.         binding.recyclerView?.apply {
    38.             adapter = galleryAdapter
    39.             //GridLayouStaager(requireContext(), 2) 对齐 StaggeredGridLayoutManager 交错感
    40.             layoutManager = StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)
    41.         }
    42.         viewModel()
    43.     }  
    44.  
    45.     private fun viewModel(){
    46.         galleryViewModel.pagedListLiveData.observe(viewLifecycleOwner, Observer {
    47.             galleryAdapter.submitList(it)
    48.             binding.swipeLayoutGallery.isRefreshing = false
    49.         })
    50.         binding.swipeLayoutGallery.setOnRefreshListener {
    51.             galleryViewModel.resetQuery()
    52.         }
    53.     }
    54. }

    4. 第二种方式 使用 Paging3 加载分页，retrofit2 进行 Http 请求

      4.1 定义实体类，在 Pixabay.kt 中添加

    1. class PixabayResponse {
    2.     val hits: List = emptyList()
    3.     val total = 0
    4.     val totalHits = 0
    5. }

      4.2 实现 Api 服务请求 ApiService.kt

    1. //https://pixabay.com/api/?key=30070990-cfc31c9f778ceeef4009d910d&q=beauty&per_page=30&page=1
    2. const val key = "30070990-cfc31c9f778ceeef4009d910d"
    3. interface ApiService {
    4.     @GET("?key=$key")
    5.     suspend fun queryPixabay(@Query("q") queryKey : String, @Query("page") page: Int, @Query("per_page") perPage: Int): PixabayResponse
    6.  
    7.     companion object {
    8.         private const val BASE_URL = "https://pixabay.com/api/"
    9.         fun create(): ApiService {
    10.             return Retrofit.Builder()
    11.                 .baseUrl(BASE_URL)
    12.                 .addConverterFactory(GsonConverterFactory.create())
    13.                 .build()
    14.                 .create(ApiService::class.java)
    15.         }
    16.     }
    17. }

      4.3 实现 PagingSource ，PixabayDataSources.kt 中添加

    1. class PixabayPagingSource(private val apiService: ApiService) : PagingSource<Int, PhotoItem>() {
    2.     private val queryKey = arrayOf("cat", "beauty", "car", "dog", "phone", "computer", "flower", "animal")
    3.     private var key = queryKey.random()
    4.  
    5.     override fun getRefreshKey(state: PagingState<Int, PhotoItem>): Int? {
    6.         key = queryKey.random();
    7.         return null
    8.     }
    9.  
    10.     override suspend fun load(params: LoadParams<Int>): LoadResult<Int, PhotoItem> {
    11.         return try {
    12.             val page = params.key ?: 1
    13.             val pageSize = params.loadSize
    14.             val repoResponse = apiService.queryPixabay(key, page, pageSize)
    15.             val repoItems = repoResponse.hits
    16.             val prevKey = if (page > 1) page - 1 else null
    17.             val nextKey = if (repoItems.isNotEmpty()) page + 1 else null
    18.             Log.i("MyTag", "page: $page  pageSize: $pageSize prevKey: $prevKey  nextKey: $nextKey")
    19.             LoadResult.Page(repoItems, prevKey, nextKey)
    20.         } catch (e: Exception) {
    21.             LoadResult.Error(e)
    22.         }
    23.     }
    24. }

      4.4 添加 ViewModel，GalleryViewModel.kt

    1. //1. Repository中实现网络请求
    2. object Repository {
    3.     private const val PAGE_SIZE = 10
    4.     private val apiService = ApiService.create()
    5.     fun getPagingData(): Flow> {
    6.         // PagingConfig的一个参数prefetchDistance，用于表示距离底部多少条数据开始预加载，
    7.         // 设置0则表示滑到底部才加载。默认值为分页大小。
    8.         // 若要让用户对加载无感，适当增加预取阈值即可。 比如调整到分页大小的5倍
    9.         return Pager(
    10.             config = PagingConfig(pageSize = PAGE_SIZE, prefetchDistance = 2 * PAGE_SIZE),
    11.             pagingSourceFactory = { PixabayPagingSource(apiService) }).flow
    12.     }
    13. }
    14.  
    15. class GalleryPagingViewModel : ViewModel() {
    16.     fun getPagingData(): Flow> {
    17.         return Repository.getPagingData().cachedIn(viewModelScope)
    18.     }
    19. }

      4.5 修改继承 ListAdapter 为 PagingDataAdapter, currentList 为 snapshot()，修改判空

      4.6 调用 GalleryFragment.kt

    1. class GalleryFragment : Fragment() {
    2.     private lateinit var binding: FragmentGalleryBinding
    3.     private lateinit var galleryAdapter:GalleryAdapter
    4.     private val galleryPagingViewModel by viewModels()
    5.  
    6.     override fun onCreateView(
    7.         inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    8.     ): View? {
    9.         binding = FragmentGalleryBinding.inflate(inflater, container, false)
    10.         return binding.root
    11.     }
    12.  
    13.     override fun onOptionsItemSelected(item: MenuItem): Boolean {
    14.         when (item.itemId) {
    15.             R.id.swipeIndicator -> {
    16.                 binding.swipeLayoutGallery.isRefreshing = true
    17.                 Handler().postDelayed({
    18.                 galleryAdapter.refresh()
    19.                 }, 300)
    20.  
    21.             }
    22.         }
    23.         return super.onOptionsItemSelected(item)
    24.     }
    25.  
    26.     //加载菜单栏
    27.     override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
    28.         super.onCreateOptionsMenu(menu, inflater)
    29.         inflater.inflate(R.menu.menu, menu)
    30.     }
    31.  
    32.     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    33.         super.onViewCreated(view, savedInstanceState)
    34.         setHasOptionsMenu(true)
    35.         galleryAdapter = GalleryAdapter()
    36.  
    37.         binding.recyclerView?.apply {
    38.             adapter = galleryAdapter
    39.             //GridLayouStaager(requireContext(), 2) 对齐 StaggeredGridLayoutManager 交错感
    40.             layoutManager = StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)
    41.         }
    42.        
    43.         pagingViewModel()
    44.     }
    45.  
    46.     private fun pagingViewModel() {
    47.        lifecycleScope.launch {
    48.             galleryPagingViewModel.getPagingData().collect {
    49.                 galleryAdapter.submitData(it)
    50.                 binding.swipeLayoutGallery.isRefreshing = false
    51.             }
    52.         }
    53.         binding.swipeLayoutGallery.setOnRefreshListener {
    54.             galleryAdapter.refresh()
    55.         }
    56.     }
    57. }

    5. 展示图

  • 相关阅读:
    再玩玩B端搭建
    1024程序员节与我的“摆烂“选择
    SpringBoot拦截器Interceptor的使用-基础篇
    linux系统编程6-守护进程、线程
    Nginx模块开发之http handler实现流量统计（入门篇）
    QT—3D绘图
    用文字描述给黑白照上色，这个免费网站火了！网友：比其他同类都好用
    Spring获取bean对象
    Zookeeper重要概念
    【008】将多个捕获文件进行合并
  • 原文地址：https://blog.csdn.net/u011193452/article/details/127108132