拖动时如何在使用 ItemTouchHelper 时取消 RecyclerView 中项目的拖动？

Question

Background

I'm trying to have a RecyclerView that has different view types, and yet has the ability for drag&drop, together with single click and long click operations.

It's similar to what you have on Phone app, where you can change the order of your favorites items. On the Phone app, when you long touch an item, a context menu appears right away, and if you continue to drag, the context menu is gone.

However, in this case, I'm required to do the opposite. Upon long pressing, if the user hasn't dragged in a very short time or if the user has stopped long pressing without dragging, we show a dialog on the screen, and I'm required to stop the dragging procedure.

The problem

While I've succeeded handling the long touch mechanism, and I show a dialog on these special cases, I failed to cause the dragging to stop.

This means, that if the user keeps touching the screen even after the dialog appears, it is still possible to keep dragging:

The entire code is available here (code without the long touch behavior available here ), but here's the main code:

class MainActivity : AppCompatActivity() {
    sealed class Item(val id: Long, val itemType: Int) {
        class HeaderItem(id: Long) : Item(id, ITEM_TYPE_HEADER)
        class NormalItem(id: Long, val data: Long) : Item(id, 1)
    }

    enum class ItemActionState {
        IDLE, LONG_TOUCH_OR_SOMETHING_ELSE, DRAG, SWIPE, HANDLED_LONG_TOUCH
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)
        val items = ArrayList<Item>(100)
        var itemDataCounter = 0L
        items.add(Item.HeaderItem(0L))
        for (i in 0 until 100) {
            items.add(Item.NormalItem(itemDataCounter, itemDataCounter))
            ++itemDataCounter
        }
        val gridLayoutManager = recyclerView.layoutManager as GridLayoutManager
        gridLayoutManager.spanSizeLookup = object : GridLayoutManager.SpanSizeLookup() {
            override fun getSpanSize(position: Int): Int {
                return when (recyclerView.adapter!!.getItemViewType(position)) {
                    ITEM_TYPE_HEADER -> gridLayoutManager.spanCount
                    ITEM_TYPE_NORMAL -> 1
                    else -> throw Exception("unknown item type")
                }
            }
        }
        recyclerView.adapter = object : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
            init {
                setHasStableIds(true)
            }

            override fun getItemViewType(position: Int): Int = items[position].itemType

            override fun getItemId(position: Int): Long = items[position].id

            override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
                val view = when (viewType) {
                    ITEM_TYPE_HEADER -> LayoutInflater.from(parent.context).inflate(R.layout.header_item, parent, false)
                    ITEM_TYPE_NORMAL -> LayoutInflater.from(parent.context).inflate(R.layout.grid_item, parent, false)
                    else -> throw Exception("unknown item type")
                }
                return object : RecyclerView.ViewHolder(view) {}
            }

            override fun getItemCount() = items.size

            override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
                when (getItemViewType(position)) {
                    ITEM_TYPE_NORMAL -> {
                        val data = (items[position] as Item.NormalItem).data
                        holder.itemView.setBackgroundColor(when (data % 4L) {
                            0L -> 0xffff0000.toInt()
                            1L -> 0xffffff00.toInt()
                            2L -> 0xff00ff00.toInt()
                            else -> 0xff00ffff.toInt()
                        })
                        holder.itemView.textView.text = "item $data"
                    }
                    ITEM_TYPE_HEADER -> {
                    }
                    else -> throw Exception("unknown item type")
                }
            }
        }
        val itemTouchHelper = ItemTouchHelper(object : ItemTouchHelper.Callback() {
            val touchSlop = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 1f, resources.displayMetrics)
            //            val touchSlop = ViewConfiguration.get(this@MainActivity).scaledTouchSlop
            val longTouchTimeout = ViewConfiguration.getLongPressTimeout() * 2
            var touchState: ItemActionState = ItemActionState.IDLE
            var lastViewHolderPosHandled: Int? = null
            val handler = Handler()
            val longTouchRunnable = Runnable {
                if (lastViewHolderPosHandled != null && touchState == ItemActionState.LONG_TOUCH_OR_SOMETHING_ELSE) {
                    //                    Log.d("AppLog", "timer timed out to trigger long touch")
                    onItemLongTouch(lastViewHolderPosHandled!!)
                }
            }

            private fun onItemLongTouch(pos: Int) {
                //                Log.d("AppLog", "longTouchTimeout:$longTouchTimeout")
                val item = items[pos] as Item.NormalItem
                //                Toast.makeText(this@MainActivity, "long touch on :$pos ", Toast.LENGTH_SHORT).show()
                AlertDialog.Builder(this@MainActivity).setTitle("long touch").setMessage("long touch on pos: $pos - item ${item.data}").show()
                touchState = ItemActionState.HANDLED_LONG_TOUCH
                lastViewHolderPosHandled = null
                handler.removeCallbacks(longTouchRunnable)
            }

            override fun onChildDrawOver(c: Canvas, recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder?, dX: Float, dY: Float, actionState: Int, isCurrentlyActive: Boolean) {
                super.onChildDrawOver(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive)
                //                Log.d("AppLog", "onChildDrawOver $dX $dY pos:${viewHolder?.adapterPosition} actionState:$actionState isCurrentlyActive:$isCurrentlyActive")
                if (touchState == ItemActionState.LONG_TOUCH_OR_SOMETHING_ELSE && (dX >= touchSlop || dY >= touchSlop)) {
                    lastViewHolderPosHandled = null
                    handler.removeCallbacks(longTouchRunnable)
                    touchState = if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) ItemActionState.DRAG else ItemActionState.SWIPE
                    Log.d("AppLog", "decided it's not a long touch, but $touchState instead")
                }
            }

            override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
                super.onSelectedChanged(viewHolder, actionState)
                //                Log.d("AppLog", "onSelectedChanged adapterPosition: ${viewHolder?.adapterPosition} actionState:$actionState")
                when (actionState) {
                    ItemTouchHelper.ACTION_STATE_IDLE -> {
                        //user finished drag or long touch
                        if (touchState == ItemActionState.LONG_TOUCH_OR_SOMETHING_ELSE)
                            onItemLongTouch(lastViewHolderPosHandled!!)
                        touchState = ItemActionState.IDLE
                        handler.removeCallbacks(longTouchRunnable)
                        lastViewHolderPosHandled = null
                    }
                    ItemTouchHelper.ACTION_STATE_DRAG, ItemTouchHelper.ACTION_STATE_SWIPE -> {
                        if (touchState == ItemActionState.IDLE) {
                            lastViewHolderPosHandled = viewHolder!!.adapterPosition
                            //                            Log.d("AppLog", "setting timer to trigger long touch")
                            handler.removeCallbacks(longTouchRunnable)
                            //started as long touch, but could also be dragging or swiping ...
                            touchState = ItemActionState.LONG_TOUCH_OR_SOMETHING_ELSE
                            handler.postDelayed(longTouchRunnable, longTouchTimeout.toLong())
                        }
                    }
                }
            }

            override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
                //                Log.d("AppLog", "onMove")
                if (touchState == ItemActionState.LONG_TOUCH_OR_SOMETHING_ELSE) {
                    lastViewHolderPosHandled = null
                    handler.removeCallbacks(longTouchRunnable)
                    touchState = ItemActionState.DRAG
                }
                if (viewHolder.itemViewType != target.itemViewType)
                    return false
                val fromPosition = viewHolder.adapterPosition
                val toPosition = target.adapterPosition
                //                val item = items.removeAt(fromPosition)
                //                recyclerView.adapter!!.notifyItemRemoved(fromPosition)
                //                items.add(toPosition, item)
                //                recyclerView.adapter!!.notifyItemInserted(toPosition)
                Collections.swap(items, fromPosition, toPosition)
                recyclerView.adapter!!.notifyItemMoved(fromPosition, toPosition)
                //                recyclerView.adapter!!.notifyDataSetChanged()
                return true
            }

            override fun isLongPressDragEnabled(): Boolean = true

            override fun isItemViewSwipeEnabled(): Boolean = false

            override fun getMovementFlags(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder): Int {
                if (viewHolder.itemViewType == ITEM_TYPE_HEADER)
                    return makeMovementFlags(0, 0)
                //                Log.d("AppLog", "getMovementFlags")
                val dragFlags = ItemTouchHelper.UP or ItemTouchHelper.DOWN or ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT
                val swipeFlags = if (isItemViewSwipeEnabled) ItemTouchHelper.START or ItemTouchHelper.END else 0
                return makeMovementFlags(dragFlags, swipeFlags)
            }

            override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
                if (touchState == ItemActionState.LONG_TOUCH_OR_SOMETHING_ELSE) {
                    lastViewHolderPosHandled = null
                    handler.removeCallbacks(longTouchRunnable)
                    touchState = ItemActionState.DRAG
                }
                val position = viewHolder.adapterPosition
                items.removeAt(position)
                recyclerView.adapter!!.notifyItemRemoved(position)
            }
        })
        itemTouchHelper.attachToRecyclerView(recyclerView)
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        menuInflater.inflate(R.menu.menu_main, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        var url: String? = null
        when (item.itemId) {
            R.id.menuItem_all_my_apps -> url = "https://play.google.com/store/apps/developer?id=AndroidDeveloperLB"
            R.id.menuItem_all_my_repositories -> url = "https://github.com/AndroidDeveloperLB"
            R.id.menuItem_current_repository_website -> url = "https://github.com/AndroidDeveloperLB/RecyclerViewDragAndDropTest"
        }
        if (url == null)
            return true
        val intent = Intent(Intent.ACTION_VIEW, Uri.parse(url))
        @Suppress("DEPRECATION")
        intent.addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY or Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET)
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_MULTIPLE_TASK)
        startActivity(intent)
        return true
    }

    companion object {
        const val ITEM_TYPE_HEADER = 0
        const val ITEM_TYPE_NORMAL = 1
    }
}

What I've tried

I tried to look at all of the documentation of RecyclerView and ItemTouchHelper. Also tried to look for similar questions here and over the Internet.

I can't see any way to tell the dragging mechanism: "I'm done with dragging now, cancel the dragging".

The question

How can I cancel the dragging that's initiated and maintained by ItemTouchHelper?

Answer 1

Override the isLongPressDragEnabled method with false :

override fun isLongPressDragEnabled() :Boolean {
    return false;
}

Source

https://android.googlesource.com/platform/frameworks/support/+/c045910/v7/recyclerview/src/android/support/v7/widget/helper/ItemTouchHelper.java

/**
     * Starts dragging the provided ViewHolder. By default, ItemTouchHelper starts a drag when a
     * View is long pressed. You can disable that behavior via
     * {@link ItemTouchHelper.Callback#isLongPressDragEnabled()}.