How to remove an item in view-pager 2 with kotlin?

Question

I use view-pager2 and When I remove the first item of view-pager, It does not delete and still remains but another item removed.

For example, here I want to remove the first item of view pager but it's not be removed:

My Main Activity:

class MainActivity : AppCompatActivity() {

private lateinit var myPagerAdapter: MyPagerAdapter
private val mFragmentList: ArrayList<FragmentOne> = ArrayList()

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    if (mFragmentList.isEmpty()) {
        mFragmentList.add(FragmentOne.newInstance(1))
        mFragmentList.add(FragmentOne.newInstance(2))
        mFragmentList.add(FragmentOne.newInstance(3))
    }

    myPagerAdapter = MyPagerAdapter(supportFragmentManager, lifecycle)
    view_pager.adapter = myPagerAdapter

    btn_show.setOnClickListener {
        val dialog = Dialog(this)
        dialog.setContentView(R.layout.fragment_dialog)
        dialog.btn_remove.setOnClickListener {
            //go to next item
            view_pager.currentItem = 1
            //remove first item
            mFragmentList.removeAt(0)
            //reload adapter
            myPagerAdapter.notifyDataSetChanged()
        }
        dialog.show()
    }

}

private inner class MyPagerAdapter(fragmentManager: FragmentManager, lifecycle: Lifecycle) :
    FragmentStateAdapter(fragmentManager, lifecycle) {

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

    override fun createFragment(position: Int): Fragment {
        return mFragmentList[position]
    }

}
}

FragmentOne:

class FragmentOne : Fragment() {

companion object {
    fun newInstance(position: Int): FragmentOne {
        val fragment = FragmentOne()
        val bundle = Bundle()
        bundle.putInt("id", position)
        fragment.arguments = bundle
        return fragment
    }
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    return inflater.inflate(R.layout.fragment_one, container, false)
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    val id = arguments?.getInt("id")
    tv?.text = id.toString()
}

}

If I don't use view-pager2, Just enough to add PagerAdapter.POSITION_NONE like this answer.

Can you help me?!

Answer 1

If you read the documentation it says

Note: The DiffUtil utility class relies on identifying items by ID. If you are using ViewPager2 to page through a mutable collection, you must also override getItemId() and containsItem().

Taken from this post - Migrate to ViewPager2

Since you are using a mutable ArrayList() you should also override the getItemId() method in your adapter, for the itemId you need a unique ID for every fragment, I solved it using the hashCode() function like this

 override fun getItemId(position: Int): Long {
        return mFragmentList[position].hashCode().toLong()
    } 

This should remove the first fragment and get the correct fragment from the list using the itemId Hope this solves your problem.

Answer 2

Actually delete functionality is working properly 0th index fragment is deleted but after calling notfiydataset changed the first fragment gets th value as 1 and second as 2.

Answer 3

I did the same for java, with viewpager2 and its works!

@Override
public long getItemId(int position) {
    Long longtype = Long.valueOf(mFragmentList.get(position).hashCode());
    return longtype;
}

@Override
public boolean containsItem(long itemId) {
    return super.containsItem(itemId);
}