Getting the Current Fragment Instance in the Viewpager

Getting the current Fragment instance in the viewpager

by selecting an option, I need to update the fragment that is
currently visible.

A simple way of doing this is using a trick related to the FragmentPagerAdapter implementation:

case R.id.addText:
     Fragment page = getSupportFragmentManager().findFragmentByTag("android:switcher:" + R.id.pager + ":" + ViewPager.getCurrentItem());
     // based on the current position you can then cast the page to the correct 
     // class and call the method:
     if (ViewPager.getCurrentItem() == 0 && page != null) {
          ((FragmentClass1)page).updateList("new item");     
     } 
return true;

Please rethink your variable naming convention, using as the variable name the name of the class is very confusing(so no ViewPager ViewPager, use ViewPager mPager for example).

How to get current Fragment name in viewpager?

Inside CustomTabLayout add

tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener()
            {
                @Override
                public void onTabSelected(TabLayout.Tab tab)
                {
                    int position = tab.getPosition();


                }

                @Override
                public void onTabUnselected(TabLayout.Tab tab) {
                }
                @Override
                public void onTabReselected(TabLayout.Tab tab) {

                }
            });

How to get Current Fragment in ViewPager2

Create property in your adapter to save all your fragments
Save current position
Get fragment from fragment list (property) by position when you need it

Something like this:

    val fragments: MutableList<Fragment> = mutableListOf()

    private val config: TribunConfig?
    override fun createFragment(position: Int): Fragment {
        val fragment = TribunNewsFragment.newInstance(if (menuTribun!!.get(position) == "News") "home"
        else menuTribun!!.get(position)!!.replace(" ", "").toLowerCase(), config)!!

        fragments.add(fragment)
        return fragment
    }

Parent:

 yourTabLayout.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
        override fun onTabSelected(tab: TabLayout.Tab?) {
            val fragment = adapter.fragments[tab!!.position]
            // cast fragment to your fragment class and do what you want
        }

        override fun onTabUnselected(tab: TabLayout.Tab?) {
        }

        override fun onTabReselected(tab: TabLayout.Tab?) {
        }
    })

Also you can use when or if-else for your fragments position or create base class with methods you need and cast getting fragment to it.

How to get the current fragment displayed in a specific tab of a viewpager?

First define a SparseArray in your ViewPagers' adapters like below. In this array we'll hold the instance of fragments.

SparseArray<Fragment> registeredFragments = new SparseArray<>();

And Override your Adapters' instantiateItem method.

@Override
public Object instantiateItem(ViewGroup container, int position) {
    Fragment fragment = (Fragment) super.instantiateItem(container, position);
    registeredFragments.put(position, fragment);
    return fragment;
}

Also Override destroyItem method of your ViewPagers

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    registeredFragments.remove(position);
    super.destroyItem(container, position, object);
}

And define a new method to get your ViewPager Fragments instance.

public Fragment getRegisteredFragment(int position) {
    return registeredFragments.get(position);
}

And finally set add a PageChangeListener to your ViewPagers:

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {
        // Here's your instance
        YourFragment fragment =(YourFragment)yourPagerAdapter.getRegisteredFragment(position);

    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
});

I hope this'll help you. Good luck.

Edit: I'm sorry i cannot understand exactly what you're planning to do but if you need to keep sub fragment (b_1, b_2) instance you can define a method to your activity such as

public void setCurrentFragment(Fragment fragment){
      this.currentFragment = fragment;
}

and in your sub view pager's adapter you can call this method like below:

subViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {
        // Here's your instance
        YourFragment fragment =(YourFragment)yourSubPagerAdapter.getRegisteredFragment(position);
        ((MyActivity)getActivity).setCurrentFragment(fragment);
    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
});

With this way you can keep one instance and your top fragment.

Is it possible to access the current Fragment being viewed by a ViewPager?

I finally found an answer that worked for me. Basically, you can access the fragment for a viewPager page by using the tag "android:switcher:"+R.id.viewpager+":0".

How to get fragment reference from ViewPager

Use viewPager.getAdapter.getItem(position); from your Activity or parent Fragment.

Description (Modified) - As you wrote addFragment() adds a fragment to mFragmentList and you are adding fragment by this method too by calling:

mSectionsPageAdapter.addFragment(new MyChatsFragment())

And getItem() returns a fragment from mFragmentList where you added your fragment. So if you want to get MyChatsFragment reference just use:

MyChatsFragment myChatsFragment = (MyChatsFragment) 
mSectionsPageAdapter .getItem(position);

MyChatsFragment myChatsFragment = (MyChatsFragment) 
viewPager.getAdapter.getItem(position);

Get current fragment in viewpager2 in android

You can use HashMap to do this:

private HashMap<Integer, Fragment> hashMap = new HashMap<>();
@Override
public Fragment createFragment(int position) {
     Fragment fragment = ScreenFragment.newInstance(position);
     hashMap.put(position, fragment);
     return fragment;
}

And then get current fragment at this way:

ScreenFragment screenFragment = (ScreenFragment) hashMap.get(viewPager.getCurrentItem());