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要实现这个拖动重排序功能，主要是用到了RecycleView的ItemTouchHelper类

首先是定义一个接口

interface ItemTouchHelperAdapter {fun onItemMove(fromPosition: Int, toPosition: Int)
}

然后我们的Adapter里面要实现这个接口

import androidx.recyclerview.widget.RecyclerView
import java.util.*class MyAdapter(private val items: MutableList<String>) : RecyclerView.Adapter<MyAdapter.ViewHolder>(), ItemTouchHelperAdapter {// ... ViewHolder and other methods ...override fun onItemMove(fromPosition: Int, toPosition: Int) {if (fromPosition < toPosition) {for (i in fromPosition until toPosition) {Collections.swap(items, i, i + 1)}} else {for (i in fromPosition downTo toPosition + 1) {Collections.swap(items, i, i - 1)}}notifyItemMoved(fromPosition, toPosition)}
}

实现ItemTouchHelper的Callback接口方法

class SimpleItemTouchHelperCallback(private val adapter: ItemTouchHelperAdapter) : ItemTouchHelper.Callback() {override fun isLongPressDragEnabled() = trueoverride fun isItemViewSwipeEnabled() = falseoverride fun getMovementFlags(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder): Int {//这里是水平拖动val dragFlags = ItemTouchHelper.LEFT or ItemTouchHelper.RIGHTreturn makeMovementFlags(dragFlags, 0)}override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {adapter.onItemMove(viewHolder.adapterPosition, target.adapterPosition)return true}override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {// do nothing}
}

其中控制拖动方向的主要是在getMovementFlags方法中的dragFlags参数

如果是水平拖动，则用

ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT

如果是竖直方向上拖动，则是用

ItemTouchHelper.UP or ItemTouchHelper.DOWN

最后绑定到我们的RecycleView上

val adapter = MyAdapter(myDataset)
val recyclerView = findViewById<RecyclerView>(R.id.my_recycler_view)
recyclerView.adapter = adapterval callback = SimpleItemTouchHelperCallback(adapter)
val touchHelper = ItemTouchHelper(callback)
touchHelper.attachToRecyclerView(recyclerView)

完成以上的步骤就瞬间实现了让RecycleView支持拖动重排序的功能

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