在 Kotlin 中使用 RecyclerView 时未调用适配器

问题描述 投票:0回答:1

我有一个名为 ShoppingListActivity 的活动。它的布局中唯一的东西是一个名为 ShoppingListFragment 的片段。该片段获取一个 listId 作为参数,并应列出 RecyclerView 中 id = listId 的列表中的所有项目以及该列表的名称。当 ShoppingListFragment 被调用时,名称会正确显示,但 recyclerview 永远不会显示。

ShoppingListActivity 的代码是:

class ShoppingListActivity : AppCompatActivity() {


    private var _binding: ActivityShoppingListBinding? = null
    private val binding get() = _binding!!

    private lateinit var shoppingListViewModel: ShoppingListViewModel
    private lateinit var shoppingListNameTextView: TextView
    private lateinit var recyclerView: RecyclerView
    private lateinit var shoppingList: ShoppingList

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_shopping_list)

        var listId = intent.getIntExtra("ShoppingListId",0)

        if(savedInstanceState == null)
        {
            supportFragmentManager.commit {
                add(R.id.shopping_list_fragment, ShoppingListFragment(listId))
                setReorderingAllowed(true)
            }
        }
    }
}

ShoppingListActivity 的 .xml 文件:

<?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"
    android:id="@+id/activity_shopping_list"
    tools:context=".Activities.ShoppingListActivity">

    <androidx.fragment.app.FragmentContainerView
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/shopping_list_fragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

ShoppingListFragment 代码:


class ShoppingListFragment(private val listId:Int) : Fragment() {


    private var _binding: FragmentShoppingListBinding? = null
    private val binding get() = _binding!!

    private lateinit var shoppingListViewModel: ShoppingListViewModel
    private lateinit var shoppingListNameTextView: TextView
    private lateinit var recyclerView: RecyclerView
    private lateinit var shoppingList: ShoppingList


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

    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_shopping_list, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        //DVATA VIEWMODELS, DA SE ZEMI LISTATA SO ITEMS I DA SE PUSTI NAPRED
        _binding = FragmentShoppingListBinding.bind(view)
        recyclerView = binding.shoppingListRecyclerView

        var context = requireContext()
        val shoppingListViewModelFactory = ShoppingListViewModelFactory(context)
        shoppingListViewModel = ViewModelProvider(this,shoppingListViewModelFactory)[ShoppingListViewModel::class.java]

        shoppingListNameTextView = binding.shoppingListName
        shoppingList = shoppingListViewModel.getListById(listId)

        shoppingListNameTextView.text = shoppingList.Name

        var itemsInList = shoppingListViewModel.getItemsInShoppingList(shoppingList)

        var adapter = SingleShoppingListAdapter(itemsInList)

        recyclerView.adapter = adapter
    }

}

ShoppingListFragment 的 .xml 文件的代码:


<?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/shopping_list_fragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".UI.Fragments.ShoppingListFragment">

    <TextView
        android:id="@+id/shopping_list_name"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="52dp"

        android:layout_marginTop="44dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.recyclerview.widget.RecyclerView
        android:layout_width="50dp"
        android:id="@+id/shopping_list_recycler_view"
        android:layout_height="150dp"
        android:layout_marginTop="60dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/shopping_list_name"
        app:layout_constraintVertical_bias="0.0" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/add_item_to_shopping_list"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="60dp"
        android:layout_marginBottom="76dp"
        android:clickable="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:srcCompat="@android:drawable/ic_menu_add" />


</androidx.constraintlayout.widget.ConstraintLayout>

recycler_view_shopping_list_item_element.xml的代码:


<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="10dp"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/shopping_list_item_name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            tools:layout_editor_absoluteX="-16dp"
            app:layout_constraintTop_toTopOf="parent"
            tools:layout_editor_absoluteY="1dp" />

        <TextView
            android:id="@+id/shopping_list_item_quantity"
            android:layout_width="10dp"
            android:layout_height="wrap_content"
            app:layout_constraintTop_toBottomOf="@+id/shopping_list_item_name"
            tools:layout_editor_absoluteX="0dp" />



    </androidx.constraintlayout.widget.ConstraintLayout>
</androidx.cardview.widget.CardView>

SingleShoppingListAdapter 的代码:


class SingleShoppingListAdapter(private val listItems: ArrayList<ShoppingListItem>) : RecyclerView.Adapter<SingleShoppingListAdapter.SingleShoppingListViewHolder>() {
    inner class SingleShoppingListViewHolder(view: View) : RecyclerView.ViewHolder(view) {

        private var name: TextView = view.findViewById(R.id.shopping_list_item_name)
        private var quantity: TextView = view.findViewById(R.id.shopping_list_item_quantity)
        fun bind(item: ShoppingListItem)
        {
            name.text = item.Name
            quantity.text = item.Quantity.toString()
        }
    }

    override fun onCreateViewHolder(
        parent: ViewGroup,
        viewType: Int
    ): SingleShoppingListViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.recycler_view_shopping_list_item_element,parent,false)
    return SingleShoppingListViewHolder(view)
}

override fun getItemCount(): Int {
        return listItems.size
    }

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

当我尝试调试它时,传递给适配器的 listItems 永远不会为空,并且适配器会被创建,但 onCreateViewHolder、getItemCount、onBindViewHolder 方法永远不会被调用。

android kotlin android-recyclerview android-adapter
1个回答
0
投票

您忘记在recyclerView中添加layoutManager,这似乎是您的内容不可见的原因。

您可以通过两种方式添加布局管理器。

类型1

<androidx.recyclerview.widget.RecyclerView
        android:layout_width="50dp"
        android:id="@+id/shopping_list_recycler_view"
        android:layout_height="150dp"
        android:layout_marginTop="60dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        //add this line.    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/shopping_list_name"
        app:layout_constraintVertical_bias="0.0" />
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