java - 如何在 GridLayoutManager 中改变每条偶数行的方向？

Question

我有 layoutManager = GridLayoutManager(context, 3)
如何使每条奇数线方向从左到右和偶数线 - 从右到左

看起来像:

0 -> 1 -> 2

5 <- 4 <- 3

6 -> 7 -> 8

etc...

有什么想法吗？

Answer 1

免责声明:我正在使用手机，因此未经测试

如果你自己写RecyclerView.Adapter ，您可以覆盖 bind 方法以“以错误的顺序”查找数据:

Pos0:数据 0 -> Pos1:数据 1 -> Pos2:数据 2
位置 3:数据 5 -> Pos4:数据 4 -> Pos5:数据 3
Pos6:数据 6 -> Pos7:数据 7 -> Pos8:数据 8
Pos9: 间隔 -> Pos10: 间隔 -> Pos11: 数据 9

我假设您正在将一些数据集合传递给您的适配器；我们还需要列数:

class SnakingAdapter(
    private val data: SomeCollection<SomeObject>, 
    private val cols: Int
) : RecyclerView.Adapter<SomeViewHolder> { ... }

首先，让我们处理您的 RecyclerView 以不完整的偶数行结束的边缘情况。例如，如果您有 10 个数据项(最大索引 9)，我假设您想要右侧的最后一项(而不是左侧)。我们可以通过在它前面创建 2 个“spacer”项目来做到这一点:

private val twoRows = cols * 2 // left > right & right > left
private val remainder = data.count() % twoRows

// If last row is an odd row => no "spacers"
// If last row is complete => no "spacers"
private val needSpacers = remainder > cols
private val paddedCount = 
    if(needSpacers) (data.count() / twoRows + 1) * twoRows
    else data.count()
private val firstSpacerPosition = data.count() / cols * cols
private val spacerPositions = 
    if(needSpacers) List(paddedCount - data.count()) {  firstSpacerPosition + it }
    else emptyList<Int>()

override fun getItemCount(): Int = paddedCount

override fun getItemViewType(position: Int): Int =
    if(spacerPositions.contains(position)) 2
    else 1

override onCreateViewHolder(parent: ViewGroup, viewType: Int) = when(viewType) { 
    1 => // create a normal item view & ViewHolder
    2 => // create a "spacer" item view & ViewHolder
}

接下来我们需要为偶数行绑定(bind)“错误”的数据:

override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position Int) { 
    // If spacer, do nothing
    if(spacerPositions.contains(position)) return

    // If even row, flip the order of the data
    val twoRowPos = position % twoRows
    val rowTwomidpoint = cols / 2 + cols // TODO: extract as a field
    val altPosition = 
      if (twoRowPos >= cols) (position - 2 * (twoRowPos - rowTwoMidpoint)) // TODO: correct for odd cols; should fix for even cols
      else position

    val data = dataSource.get(altPosition)
    // bind data to view holder here
}