Recycleview drag effect

Preface ： be based on RecycleView Achieve drag effect , It's very simple , Just use the... Provided by the system ItemTouchHelper Can meet most needs .

Realization ：

1、 establish ItemTouchHelper, stay CallBack To deal with business

（1）getMovementFlags() Set allow drag 、 The direction of the slide

（2）onMove() The drag process keeps calling , In exchange for item

（3）onSelectedChanged() Long press to select callback , Can be used as a highlight for the selected background

（4）clearView() End drag callback , Can be used to restore the selected background

2、 relation RecycleView, Give sliding ability

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val tableList = ArrayList<String>()
        for (i in 1..200) {
            tableList.add(" table （${i}）")
        }
        rv_table.layoutManager = GridLayoutManager(this, 5)
        TableAdapter().let {
            it.mTableList = tableList
            rv_table.adapter = it
        }
        val itemTouchHelper = ItemTouchHelper(object : ItemTouchHelper.Callback() {
            override fun getMovementFlags(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder
            ): Int {
                // Drag direction 
                val dargFlags =
                    ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT or ItemTouchHelper.UP or ItemTouchHelper.DOWN
                // Sliding direction 
                val swipeFlags = ItemTouchHelper.UP or ItemTouchHelper.DOWN
                // Set drag 、 Sliding direction 
                return makeMovementFlags(dargFlags, swipeFlags)
            }

            override fun onMove(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder,
                target: RecyclerView.ViewHolder
            ): Boolean {
                // Drag the ViewHolder Location 
                val fromPosition = viewHolder.adapterPosition
                // After the ViewHolder Location 
                val toPosition = target.adapterPosition
                when{
                    fromPosition < toPosition -> {// Drag backwards , And location +1 swapping 
                        for (i in fromPosition..toPosition) {
                            Collections.swap(tableList, i, i + 1)
                        }
                        recyclerView.adapter?.notifyItemMoved(fromPosition, toPosition)
                    }
                    fromPosition > toPosition -> {// Drag forward , And location -1 swapping 
                        for (i in fromPosition..toPosition) {
                            Collections.swap(tableList, i, i - 1)
                        }
                        recyclerView.adapter?.notifyItemMoved(fromPosition, toPosition)
                    }
                }
                return true
            }

            override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
                super.onSelectedChanged(viewHolder, actionState)
                // Long press to select the... To be dragged ViewHolder Background color 
                (viewHolder as? TableAdapter.TableViewHolder)?.tvTabe?.setBackgroundResource(R.color.colorPrimary)
            }

            override fun clearView(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder
            ) {
                super.clearView(recyclerView, viewHolder)
                (viewHolder as TableAdapter.TableViewHolder).tvTabe.setBackgroundResource(R.color.colorAccent)
            }
            override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {}
        })
        // give RecycleView Drag capability 
        itemTouchHelper.attachToRecyclerView(rv_table)
    }

Advanced

Scene one ： Prohibited part item Drag the （ As the first 1 Items cannot be dragged ）

1、 Disable the default drag ：CallBack in isLongPressDragEnabled() return false

2、 In the custom implementation item Long press the event , Execute the drag operation for those that meet the conditions

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val tableList = ArrayList<String>()
        for (i in 1..200) {
            tableList.add(" table （${i}）")
        }
        rv_table.layoutManager = GridLayoutManager(this, 5)
        val itemTouchHelper = ItemTouchHelper(object : ItemTouchHelper.Callback() {
            override fun getMovementFlags(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder
            ): Int {
                // Drag direction 
                val dargFlags =
                    ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT or ItemTouchHelper.UP or ItemTouchHelper.DOWN
                // Sliding direction 
                val swipeFlags = ItemTouchHelper.UP or ItemTouchHelper.DOWN
                // Set drag 、 Sliding direction 
                return makeMovementFlags(dargFlags, swipeFlags)
            }

            override fun onMove(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder,
                target: RecyclerView.ViewHolder
            ): Boolean {
                // Drag the ViewHolder Location 
                val fromPosition = viewHolder.adapterPosition
                // After the ViewHolder Location 
                val toPosition = target.adapterPosition
                when{
                    fromPosition < toPosition -> {// Drag backwards , And location +1 swapping 
                        for (i in fromPosition..toPosition) {
                            Collections.swap(tableList, i, i + 1)
                        }
                        recyclerView.adapter?.notifyItemMoved(fromPosition, toPosition)
                    }
                    fromPosition > toPosition -> {// Drag forward , And location -1 swapping 
                        for (i in fromPosition..toPosition) {
                            Collections.swap(tableList, i, i - 1)
                        }
                        recyclerView.adapter?.notifyItemMoved(fromPosition, toPosition)
                    }
                }
                return true
            }

            override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
                super.onSelectedChanged(viewHolder, actionState)
                // Long press to select the... To be dragged ViewHolder Background color 
                (viewHolder as? TableAdapter.TableViewHolder)?.tvTabe?.setBackgroundResource(R.color.colorPrimary)
            }

            override fun clearView(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder
            ) {
                super.clearView(recyclerView, viewHolder)
                (viewHolder as TableAdapter.TableViewHolder).tvTabe.setBackgroundResource(R.color.colorAccent)
            }

            override fun isLongPressDragEnabled(): Boolean {
                // Disable default drag 
                return false
            }
            override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {}
        })
        // give RecycleView Sliding capacity 
        itemTouchHelper.attachToRecyclerView(rv_table)
        TableAdapter().let {
            it.mTableList = tableList
            rv_table.adapter = it
            // Pass the drag function to Adapter
            it.mItemTouchHelper = itemTouchHelper
        }
    }

class TableAdapter : RecyclerView.Adapter<TableAdapter.TableViewHolder>(){
    var mTableList = ArrayList<String>()
    var mItemTouchHelper: ItemTouchHelper? = null

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

    override fun onBindViewHolder(holder: TableViewHolder, position: Int) {
        val table = mTableList[position]
        holder.tvTabe.text = table
    }

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

    inner class TableViewHolder constructor(view: View): RecyclerView.ViewHolder(view) {
        val tvTabe = view.findViewById<TextView>(R.id.tv_table)

        init {
            tvTabe.setOnLongClickListener {
                if (this.adapterPosition != 0){
                    mItemTouchHelper?.startDrag(this)
                    [email protected] true
                }
                [email protected] false
            }
        }
    }
}

Scene two ： Just drag the item And final position item swapping , The path location remains unchanged

1、 stay onMove() Record the passed position to the dragged ViewHolder in

2、 stay clearView() Position exchange in

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val tableList = ArrayList<String>()
        for (i in 1..200) {
            tableList.add(" table （${i}）")
        }
        rv_table.layoutManager = GridLayoutManager(this, 5)
        val itemTouchHelper = ItemTouchHelper(object : ItemTouchHelper.Callback() {
            override fun getMovementFlags(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder
            ): Int {
                // Drag direction 
                val dargFlags =
                    ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT or ItemTouchHelper.UP or ItemTouchHelper.DOWN
                // Sliding direction 
                val swipeFlags = ItemTouchHelper.UP or ItemTouchHelper.DOWN
                // Set drag 、 Sliding direction 
                return makeMovementFlags(dargFlags, swipeFlags)
            }

            override fun onMove(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder,
                target: RecyclerView.ViewHolder
            ): Boolean {
                // After the ViewHolder The position is saved to the dragged ViewHolder in 
                val toPosition = target.adapterPosition
                (viewHolder as TableAdapter.TableViewHolder).toPosition = toPosition
                return true
            }

            override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
                super.onSelectedChanged(viewHolder, actionState)
                // Long press to select the... To be dragged ViewHolder Background color 
                (viewHolder as? TableAdapter.TableViewHolder)?.tvTabe?.setBackgroundResource(R.color.colorPrimary)
            }

            override fun clearView(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder
            ) {
                super.clearView(recyclerView, viewHolder)
                (viewHolder as TableAdapter.TableViewHolder).tvTabe.setBackgroundResource(R.color.colorAccent)
                // Drag the ViewHolder Location 
                val fromPosition = viewHolder.adapterPosition
                // Final position 
                val toPosition = viewHolder.toPosition
                if (toPosition >= 0){
                    Collections.swap(tableList, fromPosition, toPosition)
                    recyclerView.adapter?.let{
                        it.notifyItemChanged(fromPosition)
                        it.notifyItemChanged(toPosition)
                    }
                }
            }

            override fun isLongPressDragEnabled(): Boolean {
                // Disable default drag 
                return false
            }
            override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {}
        })
        // give RecycleView Sliding capacity 
        itemTouchHelper.attachToRecyclerView(rv_table)
        TableAdapter().let {
            it.mTableList = tableList
            rv_table.adapter = it
            // Pass the drag function to Adapter
            it.mItemTouchHelper = itemTouchHelper
        }
    }

class TableAdapter : RecyclerView.Adapter<TableAdapter.TableViewHolder>(){
    var mTableList = ArrayList<String>()
    var mItemTouchHelper: ItemTouchHelper? = null

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

    override fun onBindViewHolder(holder: TableViewHolder, position: Int) {
        val table = mTableList[position]
        holder.tvTabe.text = table
    }

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

    inner class TableViewHolder constructor(view: View): RecyclerView.ViewHolder(view) {
        val tvTabe = view.findViewById<TextView>(R.id.tv_table)
        var toPosition = -1

        init {
            tvTabe.setOnLongClickListener {
                if (this.adapterPosition != 0){
                    mItemTouchHelper?.startDrag(this)
                    [email protected] true
                }
                [email protected] false
            }
        }
    }
}