How do I dynamically add and delete fragments with viewpager2 and fragmentstateadapter?

Question

so I've been trying to dynamically add and delete fragments from my application for months now. I recently migrated over to viewpager2 and fragmentstateadapter but to no avail. My goal is to delete a fragment at a specific location completely, but have the ability to add a new fragment to the end of the list with no previous data. When I do this however, the application duplicates fragments. Here is my adapter code:

package com.dc.shark_reel_t5.ui.main;

import android.content.Intent;
import android.content.Context;
import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.StringRes;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;
import androidx.fragment.app.FragmentStatePagerAdapter;
import androidx.fragment.app.FragmentTransaction;
import androidx.lifecycle.Lifecycle;
import androidx.recyclerview.widget.RecyclerView;
import androidx.viewpager.widget.PagerAdapter;
import androidx.viewpager2.adapter.FragmentStateAdapter;

import com.dc.shark_reel_t5.R;

import java.util.ArrayList;

/**
 * A [FragmentPagerAdapter] that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */
public class SectionsPagerAdapter extends FragmentStateAdapter {

    private FragmentManager mFragmentManager;
    private FragmentTransaction currTransaction = null;
    private int count = 0;
    private ArrayList<String> mTitles = new ArrayList<String>();
    private ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
    private ArrayList<Integer> mFragmentIDs = new ArrayList<Integer>();


    public SectionsPagerAdapter(FragmentManager fm, Lifecycle lc) {
        super(fm, lc);
        mFragmentManager = fm;
    }

    @NonNull
    @Override
    public Fragment createFragment(int position) {
        return mFragments.get(position);
    }

    @Nullable
    public CharSequence getPageTitle(int position) { return (CharSequence) mTitles.get(position); }


    public String getTitle(int position) {
        return mTitles.get(position);
    }

    //Dynamic(runtime) methods:

    //On call: adds a hook to the end of the list in UI(DOES NOT CHANGE BACK END VARIABLES YET)
    public void addHookFrag(){
        mTitles.add("Hook " + (mFragments.size() + 1));
        PlaceholderFragment currFrag = PlaceholderFragment.newInstance(mFragments.size() + 1);
        mFragmentIDs.add(currFrag.getId());
        mFragments.add(currFrag);
        notifyItemInserted(mFragments.size()-1);
    }

    public void delHookFrag(int position){
        mFragments.remove(position);
        mFragmentIDs.remove(position);
        notifyDataSetChanged();
    }

    @Override
    public int getItemCount() {
        return mFragments.size();
    }

    @Override
    public long getItemId(int position){
        if(position >= getItemCount() || position < 0)
            return RecyclerView.NO_ID;

        return mFragmentIDs.get(position);
    }

    @Override
    public boolean containsItem(long itemId){
        return mFragmentIDs.contains((int)itemId);
    }

}

Thanks.

Answer 1

I developed a solution. It turns out the ID that is passed to containsItem is from getItemID, so the whole system relies on the programmer to come up with a method for creating unique IDs. I used a counter, because the only thing that should differentiate the fragments is chronological order, which in this case increases linearly. Here are the pertinent attributes of my adapter that helped me:

public class SectionsPagerAdapter extends FragmentStateAdapter {

...

    private int idGen = 0;

    @Override
    public long getItemId(int position) {
        return (long)mFragmentIDs.get(position);
    }

    @Override
    public boolean containsItem(long itemId) {
        return mFragmentIDs.contains((int)itemId);
    }

...

}

I do not show it here, but I manage a list of Fragment IDs. When adding a new fragment, I increment idGen and add the incremented value to the list. When deleting, I remove the ID and the fragment from their respective lists, as well as updating the section number of all effected fragments(easily done with a setter method in your fragment class). Good luck to all with this problem, took me long enough!

Answer 2

The below code has the FragmentStateAdapter. Viewpager2 uses recycler view to reuse the views. You can add a new page to the data list and use notifyDataSetChanged or notifyItemInserted method to add a new page to the viewpager. Likewise notifyItemRemoved can be used to dynamically remove a page from the position and adjust the viewpager

class StoriesPagerAdapter(fragment: Fragment, var dataList:MutableList<Content> = mutableListOf()) : FragmentStateAdapter(fragment) {
override fun getItemCount(): Int {
    return dataList.size
}

override fun createFragment(position: Int): Fragment {
    return StoryViewFragment.newInstance(dataList[position], position)
}

companion object {
    var currentItem = 0
        get() = field
        set(value) {
            field = value
        }
}}