CODEWITHSUNDEEP
androidkotlinandroid-recyclerviewlistadapterandroid-diffutils
potatoxchip
potatoxchip

Reputation: 565

DiffUtil is not updating the RecyclerView

I have made an adapter for a recyclerView and used DiffUtil to show the updation of the list in a fancier way. I used google codelabs for a reference for this. But the list is not updating from the following code. Please help

class LaptopAdapter : ListAdapter<Laptop, LaptopAdapter.ViewHolder>(Diff()) {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        return ViewHolder.from(parent)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val item = getItem(position)
        holder.bind(item)
    }

    class ViewHolder private constructor(itemView: View) : RecyclerView.ViewHolder(itemView) {
        var ramText: TextView = itemView.findViewById(R.id.ramText)
        var diskText: TextView = itemView.findViewById(R.id.diskText)
        var screenText: TextView = itemView.findViewById(R.id.screenText)
        var osText: TextView = itemView.findViewById(R.id.osText)

        fun bind(item: Laptop) {
            ramText.text = item.ram.toString()
            diskText.text = item.disk
            screenText.text = item.screen.toString()
            osText.text = item.os
        }

        companion object {
            fun from(parent: ViewGroup) =
                    ViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.item, parent, false))
        }
    }
}

class Diff : DiffUtil.ItemCallback<Laptop>() {
    override fun areItemsTheSame(oldItem: Laptop, newItem: Laptop): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areContentsTheSame(oldItem: Laptop, newItem: Laptop): Boolean {
        return oldItem == newItem
    }
}

My MainActivity file is

setContentView(R.layout.activity_main)

        val list: ArrayList<Laptop> = ArrayList()
        list.add(Laptop(11, 4, "SSD", 14, "Windows"))
        list.add(Laptop(12, 4, "HDD", 14, "Ubuntu"))
        list.add(Laptop(17, 16, "SSD", 14, "Windows"))
        list.add(Laptop(13, 8, "SSD", 14, "Windows"))

        val rv: RecyclerView = findViewById(R.id.rv)
        rv.layoutManager = LinearLayoutManager(this)
        val adapter = LaptopAdapter()
        rv.adapter = adapter
        adapter.submitList(list)

        val btn: Button = findViewById(R.id.btn)
        btn.setOnClickListener {
            list.add(Laptop(15, 12, "HDD", 12, "DOS"))
            list.sortBy {
                it.ram
            }
            adapter.submitList(list)
        }

I tried previous stackOverflow answers and none were working. Please help

Upvotes: 4

Views: 5631

Answers (1)

Matt Twig
Matt Twig

Reputation: 444

If you check in source code of ListAdapter how submitList work you will find this part of code: 

if (newList == mList) {
   // nothing to do (Note - still had to inc generation, since may have ongoing work)
   return;
}

so until you pass the list with the same reference you will never update your list. To make it work you can simply invoke:

adapter.submitList(list.toList())

Upvotes: 15

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