让 RecyclerView 可以左滑删除

Recycler.kt

    /**
     * 让 RecyclerView 可以左滑删除
     * @param onItemSwiped 响应左滑删除时的调用
     * @param onItemRevoked 响应撤回删除时的调用
     */
    private fun <T : Any> RecyclerView.setSwipeAble(
            onItemSwiped: (position: Int) -> T,
            onItemRevoked: (position: Int, value: T) -> Unit,
            onItemMoved: (from: Int, to: Int) -> Boolean
    ) = ItemTouchHelper(object : ItemTouchHelper.Callback() {
        override fun getMovementFlags(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder): Int {
            val dragFlag = ItemTouchHelper.UP or ItemTouchHelper.DOWN
            val swipeFlag = ItemTouchHelper.START or ItemTouchHelper.END
            return when (layoutManager) {
                is GridLayoutManager -> makeMovementFlags(dragFlag or swipeFlag, 0)
                is LinearLayoutManager -> makeMovementFlags(dragFlag, swipeFlag)
                else -> makeMovementFlags(0, 0)
            }
        }

        //用 int 和 T 键值对临时保存所擦除的那一项的 位置 和  数据
        var removed: Pair<Int, T?> = -1 to null

        override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
            val from = viewHolder.adapterPosition
            val to = target.adapterPosition
            val b = onItemMoved(from, to)
            if (b) {
                adapter.notifyItemMoved(from, to)
            }
            return b
        }

        override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
            val adapterPosition = viewHolder.adapterPosition
            removed = adapterPosition to onItemSwiped(adapterPosition)
            adapter.notifyItemRemoved(adapterPosition)
            Snackbar.make(this@setSwipeAble, context.getString(R.string.undo_description), Snackbar.LENGTH_LONG)
                    .setAction(context.getString(R.string.undo), {
                        val position = removed.first
                        val value = removed.second
                        if (position == -1 || value == null) {
                            return@setAction
                        }
                        onItemRevoked(position, value)
                        adapter.notifyItemInserted(position)
                    })
                    .show()
        }

    }).attachToRecyclerView(this@setSwipeAble)