Fragment 中的 Android Kotlin RecyclerView 无法正常工作

Question

我对 Kotlin 和 Android 编程非常陌生。我尝试创建一个填充 Recycler View 的 fragment ，但不知怎的，我收到以下错误:E/RecyclerView:没有附加适配器；跳过布局我真的不明白为什么我会得到这个，因为我绑定(bind)了一切。如果有人可以解释我做错了什么，我将非常感激。我的代码如下:

我的类(class):

data class Movie(val id:Int, val posterPath:String, val vote:Double, val language:String,val releaseDate:String, val title:String) {}

我的 fragment :

class MovelistScreen : Fragment(R.layout.fragment_movelist_screen) {

    @ExperimentalStdlibApi
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {

// View created, can be accessed
//        val args = arguments ?: throw IllegalArgumentException("Use new instance method")
//        val argValue = args.getString(ARG_NAME)

        val binding = FragmentMovelistScreenBinding.inflate(layoutInflater)
        val lst : List<Movie> = buildList {
            add(Movie(id=1,posterPath="/asdasd",vote=7.3,language="Eng",releaseDate="2017",title="Test1"))
            add(Movie(id=2,posterPath="/asdasd",vote=6.3,language="Hun",releaseDate="2013",title="Test2"))
        }

        val listAdapter = MovieListAdapter()
        binding.itemList.adapter=listAdapter
        listAdapter.submitList(lst)
    }
    companion object {
        private const val ARG_NAME = "test_argument"
        fun newInstance(testArg: String): DetailpageFragment = DetailpageFragment().apply {
            arguments = Bundle().apply { putString(ARG_NAME, testArg) }
        }
    }
}

我的适配器

class MovieListAdapter : ListAdapter<Movie, MovieViewHolder>(diffUtil) {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MovieViewHolder {
        val layoutInflater: LayoutInflater = LayoutInflater.from(parent.context)
        return MovieViewHolder(MovieItemBinding.inflate(layoutInflater,parent,false))
    }

    override fun onBindViewHolder(holder: MovieViewHolder, position: Int) {
        val item:Movie=getItem(position)
        val binding:MovieItemBinding = holder.binding

        binding.movieTitle.text=item.title
        binding.releaseYear.text=item.releaseDate
        binding.language.text=item.language
        binding.ratingtext.text=item.vote.toString()
        binding.movieImage.load("https://i.postimg.cc/VLbN4hkz/the-hobbit-the-desolation-of-smaug.jpg")
    }
}


private val diffUtil : DiffUtil.ItemCallback<Movie> = object : DiffUtil.ItemCallback<Movie>() {
    override fun areItemsTheSame(oldItem: Movie, newItem: Movie): Boolean = oldItem.id == newItem.id
    override fun areContentsTheSame(oldItem: Movie, newItem: Movie): Boolean = oldItem == newItem
}

class MovieViewHolder(val binding: MovieItemBinding):RecyclerView.ViewHolder(binding.root)

fragment_movelist_screen.xml

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

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/item_list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
        android:orientation="vertical"
        android:padding="16dp">
    </androidx.recyclerview.widget.RecyclerView>

</androidx.constraintlayout.widget.ConstraintLayout>

mainactivity.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <fragment
        android:id="@+id/fragmentmovielist"
        android:name="com.example.ubbassignment2.MovelistScreen"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:layout="@layout/fragment_detailpage" />
</FrameLayout>

Answer 1

您正在创建一个新 View 并在onViewCreated中进行绑定(bind)，并为其设置适配器(该 View 将被垃圾收集)，您应该在onCreateView中膨胀您的 View 并设置适配器到该回收器 View 而不是您的临时 View 。

fragment :

override fun onCreateView(...): View {
    val binding = FragmentMovelistScreenBinding.inflate(layoutInflater)
    val lst : List<Movie> = buildList {
        add(Movie(id=1,posterPath="/asdasd",vote=7.3,language="Eng",releaseDate="2017",title="Test1"))
        add(Movie(id=2,posterPath="/asdasd",vote=6.3,language="Hun",releaseDate="2013",title="Test2"))
    }

    val listAdapter = MovieListAdapter()
    binding.itemList.adapter=listAdapter
    listAdapter.submitList(lst)
  
    return binding.root
}