RecyclerView - 字母索引未出现

Question

作为我的RecyclerView 的一部分，我希望它下面会出现一行字母，但由于某种原因，尽管将属性设置为在屏幕上显示，但该行并未出现。

Kotlin 活动

class MainActivity : AppCompatActivity() {
    private lateinit var adapterFruit: AdapterFruit
    private lateinit var adapterAlphabet: AdapterAlphabet
    private val arrayItemsFruit = ArrayList<ItemFruit>()
    private val arrayItemsBtns = ArrayList<ItemAlphabet>()

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

        val mToolbar = findViewById<Toolbar>(R.id.myToolbar)
        val mRecyclerViewV = findViewById<RecyclerView>(R.id.mRecyclerViewWithToolbarV)
        val mRecyclerViewH = findViewById<RecyclerView>(R.id.mRecyclerViewWithToolbarH)

        // ...Do other stuff here
        setSupportActionBar(mToolbar)

        val mTitle = findViewById<TextView>(R.id.myToolbar_title)
        mTitle.text = getString(R.string.fruit)

        // Alphabet array
        arrayItemsBtns.add(ItemAlphabet("A"))
        arrayItemsBtns.add(ItemAlphabet("B"))
        arrayItemsBtns.add(ItemAlphabet("C"))
        arrayItemsBtns.add(ItemAlphabet("D"))
        arrayItemsBtns.add(ItemAlphabet("F"))
        arrayItemsBtns.add(ItemAlphabet("G"))
        arrayItemsBtns.add(ItemAlphabet("K"))
        arrayItemsBtns.add(ItemAlphabet("L"))
        arrayItemsBtns.add(ItemAlphabet("M"))
        arrayItemsBtns.add(ItemAlphabet("O"))
        arrayItemsBtns.add(ItemAlphabet("P"))
        arrayItemsBtns.add(ItemAlphabet("Q"))
        arrayItemsBtns.add(ItemAlphabet("R"))
        arrayItemsBtns.add(ItemAlphabet("S"))
        arrayItemsBtns.add(ItemAlphabet("T"))
        arrayItemsBtns.add(ItemAlphabet("W"))

        // Fruit array items
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.apple)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.blackberry)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.cherry)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.date)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.fig)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.grapefruit)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.kiwi)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.lemon)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.mango)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.pineapple)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.quince)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.raspberry)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.strawberry)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.tomato)
                )
        )
        arrayItemsFruit.add(
                ItemFruit(
                        getString(R.string.watermelon)
                )
        )

        // Set Vertical RecyclerView
        val isScreenSmall = resources.getBoolean(R.bool.isScreenSmall)
        if (isScreenSmall) {
            // Use special item decoration for small devices
            mRecyclerViewV.layoutManager =
                    LinearLayoutManager(this)

            val mListener = AdapterView.OnItemClickListener { _, _, _, _ -> }
            adapterFruit = AdapterFruit(arrayItemsFruit, mListener)

            mRecyclerViewV.addItemDecoration(
                    androidx.recyclerview.widget.DividerItemDecoration(
                            this,
                            LinearLayout.VERTICAL
                    )
            )
            mRecyclerViewV.adapter = adapterFruit
        }
        else {
            // Use special item decoration for large devices
            val numberOfColumns = 2
            mRecyclerViewV.layoutManager =
                    androidx.recyclerview.widget.GridLayoutManager(this, numberOfColumns)

            val mListener = AdapterView.OnItemClickListener { _, _, _, _ -> }
            adapterFruit = AdapterFruit(arrayItemsFruit, mListener)

            mRecyclerViewV.adapter = adapterFruit
        }

        // Set Horizontal RecyclerView
        mRecyclerViewH.layoutManager = LinearLayoutManager(this,
                RecyclerView.HORIZONTAL,
                        false)

        val mListener = AdapterView.OnItemClickListener { _, _, _, _ -> }
        adapterAlphabet = AdapterAlphabet(arrayItemsBtns, mListener)
        mRecyclerViewH.adapter = adapterAlphabet

    }
}

主布局

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/ll_activityToolbarAndRecyclerview"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <include
        layout="@layout/my_toolbar"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/mRecyclerViewWithToolbarV"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:scrollbars="vertical"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/myToolbar"
        app:layout_constraintBottom_toTopOf="@+id/mRecyclerViewWithToolbarH"/>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/mRecyclerViewWithToolbarH"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:scrollbars="horizontal"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/mRecyclerViewWithToolbarV"
        app:layout_constraintBottom_toBottomOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

按钮布局

<?xml version="1.0" encoding="utf-8"?>
<com.google.android.material.button.MaterialButton
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/myBtn"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:clickable="true"
    android:focusable="true"
    android:gravity="start|center_vertical"
    android:padding="20dp"
    android:layout_margin="20dp"
    android:textAllCaps="false"
    android:textColor="?android:attr/textColorPrimary"
    android:textSize="22sp"
    app:strokeColor="?android:attr/textColorPrimary"
    style="@style/Widget.MaterialComponents.Button.OutlinedButton" />

项目字母

data class ItemAlphabet(
        val alphabetLetter: String
)

字母索引适配器

class AdapterAlphabet(
        var listAlphabet: MutableList<ItemAlphabet>,
        private val clickListener: AdapterView.OnItemClickListener
) : RecyclerView.Adapter<AdapterAlphabet.CompanyViewHolder>() {
    class CompanyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        var btnAlphabet: MaterialButton = itemView.findViewById(R.id.myBtn)

        fun bind(alphabet: ItemAlphabet)
        {
            // Binding the data with the view holder views
            btnAlphabet.text = alphabet.alphabetLetter

            // Click events for list items (based on position)
            itemView.setOnClickListener {v ->
//                val intent: Intent = when (alphabet.alphabetLetter) {
//                    v.resources.getString(R.string.apple) -> {
//
//                    }
//                    else -> {
////                        Intent
//                    }
//                }
//                itemView.context.startActivity(intent)
            }
        }
    }

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

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

    override fun onBindViewHolder(holder: CompanyViewHolder, position: Int) {
        // Getting the product of the specified position
        val product = listAlphabet[position]

        // Binding to click listener
        holder.bind(product)
    }
}

平板电脑结果

更新

阿里阿山的建议

Answer 1

根据更新问题中的屏幕截图，我建议采用以下布局结构：

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/ll_activityToolbarAndRecyclerview"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <include
        layout="@layout/my_toolbar"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/mRecyclerViewWithToolbarV"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:scrollbars="vertical"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/myToolbar"
        app:layout_constraintBottom_toTopOf="@+id/mRecyclerViewWithToolbarH"/>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/mRecyclerViewWithToolbarH"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:scrollbars="horizontal"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

工具栏和底部RecyclerView 都没有指定对中间RecyclerView 的约束。效果应该是将工具栏固定到屏幕顶部，底部RecyclerView 固定到屏幕底部。

（注意，底部RV的高度可以使用wrap_content，因为“滚动”/“回收”轴是水平的。）

然后，您可以让中间RecyclerView 将其所有四个边缘约束到父级、工具栏和底部RecyclerView。这将导致中间 RV “伸展”以填满屏幕上的所有剩余空间。