Android ScrollView如何实现长文本逐屏滚动？

需要实现ScrollView内TextView长文本的逐屏滚动，但当前使用fullScroll(View.FOCUS_DOWN)会直接滚到文本底部，现有代码和布局如下：

当前滚动代码：

binding.scrollView.post{
    binding.scrollView.fullScroll(View.FOCUS_DOWN)
}

ScrollView布局代码：

<ScrollView
    android:id="@+id/scroll_view"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:fillViewport="true"
    android:paddingBottom="24dp"
    android:background="@color/whitef5_background"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintBottom_toTopOf="@id/holder_player_bar"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent">

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

        <com.makeramen.roundedimageview.RoundedImageView
            android:id="@+id/img"
            android:layout_width="match_parent"
            android:layout_height="220dp"
            android:layout_marginHorizontal="16dp"
            android:scaleType="centerCrop"
            android:layout_marginTop="24dp"
            android:src="@drawable/placeholder"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:riv_corner_radius="8dp"/>

        <TextView
            android:id="@+id/txt_title"
            style="@style/TextBold16Black2128"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textColorLink="@color/app_orange"
            android:layout_marginTop="12dp"
            android:gravity="center"
            android:layout_marginHorizontal="16dp"
            android:text="Reading Title"
            app:layout_constraintTop_toBottomOf="@id/img"/>

        <TextView
            android:id="@+id/txt_title_fa"
            style="@style/TextMed14Gray8f"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:layout_marginHorizontal="16dp"
            android:text="مطلب ساختگی"
            app:layout_constraintTop_toBottomOf="@id/txt_title"
            android:layout_marginTop="12dp"/>

        <View
            android:id="@+id/div"
            android:layout_width="0dp"
            android:layout_height="1dp"
            android:layout_marginTop="12dp"
            android:layout_marginHorizontal="16dp"
            android:background="@color/grayDBEC"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/txt_title_fa"/>

        <TextView
            android:id="@+id/txt"
            style="@style/TextMed14Black2128"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginHorizontal="16dp"
            android:text="@string/reading_test_speech"
            app:layout_constraintTop_toBottomOf="@id/div"
            android:layout_marginTop="24dp"/>

        <Button
            android:id="@+id/btn_test"
            style="@style/ButtonMed14White"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginHorizontal="16dp"
            android:layout_marginBottom="24dp"
            android:background="@drawable/selector_orange_button"
            android:text="@string/reading_go_to_questions_btn_text"
            app:layout_constraintTop_toBottomOf="@id/txt"
            android:layout_marginTop="24dp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintVertical_bias="1.0" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</ScrollView>

可行实现方法 #

方法1：计算单屏高度，分步滚动 #

核心思路是获取ScrollView的可视高度，每次滚动一个屏幕的距离，通过变量记录当前滚动位置：

1. 获取ScrollView可视高度：

val screenHeight = binding.scrollView.height - binding.scrollView.paddingTop - binding.scrollView.paddingBottom

2. 定义变量记录当前滚动偏移量：

private var currentScrollOffset = 0

3. 实现逐屏滚动方法（以上下页按钮触发为例）：

// 滚动到下一页
fun scrollToNextPage() {
    val maxScroll = binding.scrollView.getChildAt(0).height - screenHeight
    currentScrollOffset += screenHeight
    currentScrollOffset = currentScrollOffset.coerceAtMost(maxScroll) // 避免超出文本底部
    binding.scrollView.smoothScrollTo(0, currentScrollOffset)
}

// 滚动到上一页
fun scrollToPrevPage() {
    currentScrollOffset -= screenHeight
    currentScrollOffset = currentScrollOffset.coerceAtLeast(0) // 避免滚到顶部以上
    binding.scrollView.smoothScrollTo(0, currentScrollOffset)
}

方法2：改用ViewPager2拆分文本（推荐） #

如果文本可以拆分，直接用ViewPager2将长文本分割为多个页面，原生支持逐屏滑动，体验更流畅：

1. 按屏幕高度拆分长文本：

fun splitTextIntoPages(text: String, textView: TextView): List<String> {
    val paint = textView.paint
    val pageWidth = textView.width - textView.paddingLeft - textView.paddingRight
    val pageHeight = binding.scrollView.height - binding.scrollView.paddingTop - binding.scrollView.paddingBottom
    val lineHeight = paint.fontSpacing.toInt()
    val linesPerPage = pageHeight / lineHeight

    val layout = StaticLayout.Builder.obtain(text, 0, text.length, paint, pageWidth)
        .setLineSpacing(0f, 1f)
        .build()

    val pages = mutableListOf<String>()
    var startLine = 0
    while (startLine < layout.lineCount) {
        val endLine = min(startLine + linesPerPage, layout.lineCount)
        val start = layout.getLineStart(startLine)
        val end = layout.getLineEnd(endLine - 1)
        pages.add(text.substring(start, end))
        startLine = endLine
    }
    return pages
}

2. 给ViewPager2设置适配器：

class TextPagerAdapter(private val pages: List<String>) : RecyclerView.Adapter<TextPagerAdapter.ViewHolder>() {
    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val textView: TextView = itemView.findViewById(R.id.page_text)
    }

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

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.textView.text = pages[position]
    }

    override fun getItemCount() = pages.size
}

对应的页面布局item_text_page.xml：

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/page_text"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    style="@style/TextMed14Black2128"/>

方法3：自定义ScrollView拦截滚动事件 #

如果要保留ScrollView结构，可自定义ScrollView，拦截触摸事件，强制滚动锁定到整屏位置：

class PageScrollView(context: Context, attrs: AttributeSet?) : ScrollView(context, attrs) {
    private var lastY = 0
    private var screenHeight = 0

    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(w, h, oldw, oldh)
        screenHeight = h - paddingTop - paddingBottom
    }

    override fun onTouchEvent(ev: MotionEvent): Boolean {
        when (ev.action) {
            MotionEvent.ACTION_DOWN -> {
                lastY = ev.y.toInt()
                return super.onTouchEvent(ev)
            }
            MotionEvent.ACTION_UP -> {
                val deltaY = lastY - ev.y.toInt()
                val currentScroll = scrollY
                val targetScroll = when {
                    deltaY > screenHeight/2 -> ((currentScroll / screenHeight) + 1) * screenHeight
                    deltaY < -screenHeight/2 -> ((currentScroll / screenHeight) - 1) * screenHeight
                    else -> (currentScroll / screenHeight) * screenHeight
                }
                val maxScroll = getChildAt(0).height - screenHeight
                smoothScrollTo(0, targetScroll.coerceIn(0, maxScroll))
                return true
            }
        }
        return super.onTouchEvent(ev)
    }
}

然后在XML中替换原ScrollView为自定义的PageScrollView即可。

内容的提问来源于stack exchange，提问作者Niloofar Hakkaki