PagingData获取网络数据，能够获取到数据，但就是不执行 Adapter这个类文件 ， 这也导致布局没有加载进来


另外新建了一个项目，将代码复刻进去，能够执行Adapter类文件，并且数据显示在 recyclerView上面


这可能会是什么缘由呢？  Clean Priject 过了还是一样

BookListAdapter：

class BookListAdapter( val fragment: BookListFragment): PagingDataAdapter<Book.Cate, RecyclerView.ViewHolder>(COMPARATOR) {

    private val TAG_BookList = " BookListAdapter"

    class ViewHolder(view: View): RecyclerView.ViewHolder(view) {
        val cover: ImageView = view.findViewById(R.id.iv_cover_book)
        val cateName: TextView = view.findViewById(R.id.tv_cateName_book)
        val wordNum: TextView = view.findViewById(R.id.tv_wordNum_book)
    }

    //  绑定每一个item布局
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_book_list, parent , false)
        Log.d(TAG_BookList," onBindViewHolder cateName}  ")
        return ViewHolder(view)
    }

    //  实现具体功能 & 点击事件
    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        val item = getItem(position)!!
        Log.d(TAG_BookList," onBindViewHolder ${item.bookList[position].cateName}  ")
        when(holder){
            is ViewHolder ->{
                holder.cateName.text = item.bookList[position].cateName
                holder.wordNum.text = item.bookList[position].wordNum.toString()
                Glide
                .with(fragment)
                .load(item.bookList[position].cover)
                .into(holder.cover)
                Log.d(TAG_BookList," onBindViewHolder ${item.bookList[position].cateName}  ")
            }
        }
    }

    /**
     *  DiffUtil.ItemCallback 用于判断 是否需要加载新的Item
     *  DiffUtil.ItemCallback 就是用来比对数据变化，从而决定更新对应UI；并执行条目动画；
     */
    companion object{
        private val  COMPARATOR = object : DiffUtil.ItemCallback<Book.Cate>(){
            // 比对新旧条目是否是同一个条目,一般比对条目的唯一标示id即可，如果条目不同则可能不会更新UI；
            override fun areItemsTheSame(oldItem: Book.Cate, newItem: Book.Cate): Boolean {
                return oldItem.cateName == newItem.cateName
            }

            /**
             * 当上面的方法确定是同一个条目之后，这里比对条目的内容是否一样，不一样则会更新条目UI
            建议这里的比对把UI展示的数据都写上，写漏了会导致UI不更新对应字段；
             */
            override fun areContentsTheSame(oldItem: Book.Cate, newItem: Book.Cate): Boolean {
                return oldItem == newItem
            }
        }
    }
}

BookListPagingSource：

class BookListPagingSource(private val esService: EStudyService , val i: Int): PagingSource<String, Book.Cate>() {

    private val TAG =" BookListPagingSource "

    // load(包含有关要执行的加载操作的信息，其中包括要加载的键和要加载的项数)
    override suspend fun load(params: LoadParams<String>): LoadResult<String, Book.Cate> {
   
        return try {
            val url = params.key ?: EStudyService.BOOK_URL    // API
            Log.d(TAG, "load:  url: $url")
            val cateResponse = esService.getBook(url)
            var cateItems = cateResponse.cates.size
            val cateItem = cateResponse.cates
            val preKey = null
            var nextKey: Book.Cate? = null

              enter_Num++   //  全局变量
             
              // 第一次进入该方法
              if ( enter_Num == 1){
                  index_book = cateItems-1
              }
              nextKey =  cateResponse.cates[index_book--]
  
              /**
               *  LoadResult作为 load() 的返回值
               *  LoadResult.Page（从响应数据解析出来的对象类型，上一页的页数，下一页的页数）,并返回结果
               */
              Log.d(TAG, " load - ,${index_book} , $cateItems  $nextKey")
              LoadResult.Page(cateItem, preKey, nextKey.toString())
          } catch (e: Exception) {
              Log.d(TAG, " load -  ,抛出异常 $e  ")
              LoadResult.Error(e)
          }
      }
   
      override fun getRefreshKey(state: PagingState<String, Book.Cate>): String? = null
  
  }

BookListFragment：

class BookListFragment: BaseFragment() {

    private var _binding: LayoutBookListBinding? = null

    private val binding get() = _binding!!
   
    private val viewModel by lazy {
        ViewModelProvider(this, InjectorUtil.getBookViewModelFactory()).get(BookListViewModel::class.java)
    }

    private lateinit var adapter: BookListAdapter

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        _binding = LayoutBookListBinding.inflate(layoutInflater,container,false)
        return  super.onCreateView(binding.root)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        adapter = BookListAdapter(this)
        val layoutManager = LinearLayoutManager(activity)
        Log.d(TAG,"onViewCreate -- $layoutManager  ,$adapter , $activity  $context")
        binding.recyclerViewBook.layoutManager = layoutManager
       
        lifecycleScope.launch {
            /*
                pay attention to the selection of the collect
                submitData() receive a PagingData parameter, which can be obtained from the collect()
                注意：submitData之后不会返回，所以在它的后面写代码不会被执行
             */
            viewModel.getBookPagingData().collect {
                adapter.submitData(it)
                Log.d(TAG, " 这段代码不会被执行  ")
            }
            Log.d(TAG, " 这段代码不会被执行  ")
        }
    }

    override fun onDestroy() {
        super.onDestroy()
        _binding = null
    }


}

layout_book_list.xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:cardBackgroundColor="@color/purple_200"
    app:cardCornerRadius="4dp"
    app:cardElevation="4dp"
    app:cardPreventCornerOverlap="true"
    app:cardUseCompatPadding="true"  >
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/app_name"/>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView_book"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</androidx.cardview.widget.CardView>

item_book_list.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/iv_cover_book"
        android:layout_width="140dp"
        android:layout_height="141dp"
        android:padding="@dimen/space_16dp"
        android:src="@color/black"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tv_cateName_book"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/space_32dp"
        android:text="@string/cateName"
        android:textSize="@dimen/text_size_16dp"
        android:textStyle="bold"
        app:layout_constraintStart_toEndOf="@+id/iv_cover_book"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tv_wordNum_book"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/space_32dp"
        android:text="@string/wordNum"
        app:layout_constraintStart_toEndOf="@+id/iv_cover_book"
        app:layout_constraintTop_toBottomOf="@+id/tv_cateName_book" />
</androidx.constraintlayout.widget.ConstraintLayout>