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Андрей's questions

Martin Hope
Андрей
Asked: 2024-11-10 23:27:40 +0000 UTC
  • 5

我正在编写一个简单的项目来可视化笑话列表。当我尝试将所有内容包装在片段中时，遇到了一个问题：元素停止绘制，我发现问题出在ListAdapter中。 onCreateViewHolder方法没有被调用，onBindViewHolder也是如此。使用 ContainerView 进行标记：

<?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:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.MainActivity" >

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

片段标记：

<?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:id="@+id/main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/purple_100"
android:paddingHorizontal="20dp"
android:paddingVertical="6dp"
tools:context=".ui.main.ListFragment">

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    tools:listitem="@layout/joke_item" />
</androidx.constraintlayout.widget.ConstraintLayout>

片段代码：

class ListFragment : Fragment(R.layout.fragment_list) {

    private lateinit var binding: FragmentListBinding
    private lateinit var viewModel: JokesListViewModel
    private val adapter = JokesListAdapter {
        findNavController().navigate(
            ListFragmentDirections.actionListFragmentToJokeDetailsFragment(
                viewModel.getJokeId(it)
            )
        )
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        initViewModel()
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        binding = FragmentListBinding.inflate(layoutInflater)
        binding.recyclerView.adapter = adapter
        binding.recyclerView.layoutManager = LinearLayoutManager(activity)
        savedInstanceState ?: run {
            viewModel.generateJokes()
        }
    }

    private fun initViewModel() {
        val factory = JokeViewModelFactory(JokesGenerator)
        viewModel = ViewModelProvider(this, factory)[JokesListViewModel::class.java]
        viewModel.jokes.observe(this) {
            adapter.submitList(it)
            Toast.makeText(activity, "jokes updated", Toast.LENGTH_SHORT).show()
        }
        viewModel.error.observe(this) {
            Toast.makeText(activity, it, Toast.LENGTH_SHORT).show()
        }
    }
}

适配器代码：

class JokesListAdapter(
    private val clickListener: (Int) -> Unit
) :
    ListAdapter<Joke, JokesViewHolder>(JokeItemCallback) {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): JokesViewHolder {
        val inflater = LayoutInflater.from(parent.context)
        val binding = JokeItemBinding.inflate(inflater, parent, false)
        return JokesViewHolder(binding).apply {
            binding.root.setOnClickListener {
                handlePersonClick(bindingAdapterPosition)
            }
        }
    }

    override fun getItemCount() = currentList.size

    override fun onBindViewHolder(holder: JokesViewHolder, position: Int) {
        holder.bind(currentList[position])
    }

    private fun handlePersonClick(position: Int) {
        if (position != RecyclerView.NO_POSITION) {
            clickListener(position)
        }
    }
}

和视图持有者：

class JokesViewHolder(private val binding: JokeItemBinding) : RecyclerView.ViewHolder(binding.root) {

    fun bind(joke: Joke) {
        binding.textViewQuestion.text = joke.jokeQuestion
        binding.textViewAnswer.text = joke.jokeAnswer
        binding.textViewCategory.text = joke.category
        println("!!! $joke.id binded")
    }
}
android