ItemTouchHelper onMove Update items positions

Question

When using the itemTouchHelper onMove method. How can you while using a numbered list based on the position in the list.

For example, item 1, item 2, item 3, etc. all based on the actual position in the list the item is in. How can you then when moving the item by dragging it up or down. Update the rest of the items in the list to reflect the proper position in the list it’s in?

I'm using the below code:

override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {

            val fromPosition = viewHolder.adapterPosition
            val toPosition = target.adapterPosition

            Collections.swap(steps!!, fromPosition, toPosition)

            recyclerView.adapter!!.notifyItemMoved(fromPosition,toPosition)

            return true
        }

Snippet:

Video:

UPDATE (Adapter code):

val TAG:String = "StepAdapter"
var steps: MutableList<Step> = ArrayList()

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): StepViewHolder {
    return StepViewHolder(
        LayoutInflater.from(parent.context)
            .inflate(R.layout.recipe_property_step_list_item, parent, false))
}

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

override fun onBindViewHolder(holder: StepViewHolder, position: Int) {
    holder.bind(steps.get(position), position)
    Log.i(TAG,"onBindViewHolder - ${steps.get(position)}")
}

override fun onBindViewHolder(holder: StepViewHolder, position: Int, payloads: MutableList<Any>) {
    Log.i(TAG,"onBindViewHolder - Payloads - $payloads")
    val text:String = StringBuilder("${position + 1}.) ${steps[position].text}").toString()
    Log.i(TAG,"onBindViewHolder - Text - $text")
    holder.st_text.text = text
}

fun updateSteps(newSteps: MutableList<Step>){
    val diffResult = DiffUtil.calculateDiff(StepDiffCallBack(this.steps,newSteps))
    this.steps.clear()
    this.steps.addAll(newSteps)
    notifyDataSetChanged()
    diffResult.dispatchUpdatesTo(this)
}

LOGS:

2020-04-12 16:57:21.787 15808-15808/com.keep.recipeapp I/StepAdapter: onBindViewHolder - Payloads - []
2020-04-12 16:57:21.787 15808-15808/com.keep.recipeapp I/StepAdapter: onBindViewHolder - Text - 1.) Prepping the kitchen sink
2020-04-12 16:57:21.789 15808-15808/com.keep.recipeapp I/StepAdapter: onBindViewHolder - Payloads - []
2020-04-12 16:57:21.789 15808-15808/com.keep.recipeapp I/StepAdapter: onBindViewHolder - Text - 2.) prep the nuts and bolts
2020-04-12 16:57:21.791 15808-15808/com.keep.recipeapp I/StepAdapter: onBindViewHolder - Payloads - []
2020-04-12 16:57:21.791 15808-15808/com.keep.recipeapp I/StepAdapter: onBindViewHolder - Text - 3.) Cook the kitchen sink

TEST DATA

Answer 1

The only way to achieve this is to rebind your ViewHolders so their TextViews display the changed positions. But calling notifyDataSetChanged() or notifyItemRangeChanged(0, pos) will get all your items fade out and fade in as they were all rebinded, I would not recommend this as its quite ugly (but still, it will work)

Have you ever used method onBindViewHolder(holder: ViewHolder, position: Int, payloads: MutableList<Any>)? This allows to update only some Views inside your ViewHolder without redrawing the whole View, so the changes in your RecyclerView will be much smoother.

In your onMove method you call notifyItemRangeChanged providing range of the items that should be updated, and provide Any() as the payload, as no extra info is needed for rebinding the view, as you will have the position and data accessible in the adapter's method.

    override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
        val fromPosition = viewHolder.adapterPosition
        val toPosition = target.adapterPosition
        Collections.swap(steps!!, fromPosition, toPosition)

        recyclerView.adapter!!.notifyItemMoved(fromPosition,toPosition)
        recyclerView.adapter!!.notifyItemRangeChanged(0, max(fromPosition, toPosition), Any())
        // as you dont need to change items that are below the maximum positions
        // their positions will be correct
        return true
    }

Take in mind that you should call super method if the payloads are empty.

    override fun onBindViewHolder(holder: MyViewHolder, position: Int, payloads: MutableList<Any>) {
        if (payloads.isEmpty()) super.onBindViewHolder(holder, position, payloads)
        else {
            holder.theTextView.text = "$position.)${myList[position].data}"
        }
    }

update

Are you sure you call notifyItemRangeChanged(min(fromPos, toPos), max(fromPos,toPos)? This thing will call onBindViewHolder for every item in range. You should call it after you've called notifyItemMoved. When its working, try passing an object as a payload.

The logs don't show the behavior, it seems like its the output when the adapter binds views after initialization.