Replace one Fragment with another in ViewPager

I'm having some problems when I try to replace one Fragment with another one in a ViewPager.

Current situation

I have a ViewPager with 3 pages, each one is a Fragment. In first page, I have a ListView inside a ListFragment ("FacturasFragment"). When I click on an item of that list, I use onListItemClick method for handle that event.

What I want

• When list item is clicked, I want to replace ListFragment (contains a list of invoices) with another Fragment ("DetallesFacturaFragment", contains details of invoice).
• When I'm in "DetallesFacturaFragment" and press Back Button, should return to ListFragment.
• Scrolling between pages should not change Fragment displayed in first one. It is, if I'm in first page with "DetallesFacturaFragment" and scroll to second page, when return to first one should continue displaying "DetallesFacturaFragment".

Code

FragmentActivity

public class TabsFacturasActivity extends SherlockFragmentActivity {

	private MyAdapter mAdapter;
	private ViewPager mPager;
	private PageIndicator mIndicator;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.fragment_pager);
        mAdapter = new MyAdapter(getSupportFragmentManager());

		mPager = (ViewPager)findViewById(R.id.pager);
		mPager.setAdapter(mAdapter);

		mIndicator = (TitlePageIndicator)findViewById(R.id.indicator);
		mIndicator.setViewPager(mPager);
    }
	
	private static class MyAdapter extends FragmentPagerAdapter {

		private String[] titles = { "VER FACTURAS", "VER CONSUMO", "INTRODUCIR LECTURA" };
	    private final FragmentManager mFragmentManager;
	    private Fragment mFragmentAtPos0;
	    private Context context;

		public MyAdapter(FragmentManager fragmentManager) {
			super(fragmentManager);
			mFragmentManager = fragmentManager;
		}

		@Override
		public CharSequence getPageTitle(int position) {
			return titles[position];
		}

		@Override
		public Fragment getItem(int position) {
			switch (position) {
	        case 0: // Fragment # 0
	        	return new FacturasFragment();
	        case 1: // Fragment # 1
	            return new ConsumoFragment();
	        case 2:// Fragment # 2
	            return new LecturaFragment();
	        }
			return null;
		}

		@Override
		public int getCount() {
			return titles.length;
		}
		
		@Override
		public int getItemPosition(Object object)
		{
			if (object instanceof FacturasFragment && mFragmentAtPos0 instanceof DetallesFacturaFragment)
				return POSITION_NONE;
			return POSITION_UNCHANGED;
		}
	}

}

ListFragment

public class FacturasFragment extends ListFragment {

	private ListView lista;

    private ArrayList<TuplaFacturaWS> facturas;

	@Override
	public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRetainInstance(true);	
	}
	
	public View onCreateView(LayoutInflater inflater, ViewGroup container,
			Bundle savedInstanceState)
	{
		View view = inflater.inflate(R.layout.activity_facturas, container, false);
        facturas = myApplication.getFacturas();

		lista = (ListView) view.findViewById(id.list);

		MyAdapter myAdaptador = new MyAdapter(this, facturas);
		setListAdapter(myAdaptador);

		return view;
	}
	
	public void onListItemClick (ListView l, View v, int position, long id) {
		myApplication.setFacturaActual(position);
		mostrarDatosFactura();
	}


	private void mostrarDatosFactura() {
	    final DetallesFacturaFragment fragment = new DetallesFacturaFragment();
	    FragmentTransaction transaction = null;
        transaction = getFragmentManager().beginTransaction();
        transaction.replace(R.id.pager, fragment); //id of ViewPager
        transaction.addToBackStack(null);
        transaction.commit();
	}
	
	private class MyAdapter extends BaseAdapter {
		private final FacturasFragment actividad;
		private final ArrayList<TuplaFacturaWS> facturas;

		public MyAdapter(FacturasFragment facturasActivity, ArrayList<TuplaFacturaWS> facturas) {
			super();
			this.actividad = facturasActivity;
			this.facturas = facturas;
		}

		@Override
		public View getView(int position, View convertView, 
				ViewGroup parent) {
			LayoutInflater inflater = actividad.getLayoutInflater(null);
			View view = inflater.inflate(R.layout.list_row, null, true);
			//Set data to view
			return view;
		}

		@Override
		public int getCount() {
			return facturas.size();
		}

		@Override
		public Object getItem(int pos) {
			return facturas.get(pos);
		}

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

		private OnClickListener checkListener = new OnClickListener()
		{

			@Override
			public void onClick(DialogInterface dialog, int which) {
				// TODO Auto-generated method stub
				
			}
			
		};
	}
}

Fragment

public class DetallesFacturaFragment extends SherlockFragment {

@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
        setRetainInstance(true);	
	}
	
	public View onCreateView(LayoutInflater inflater, ViewGroup container,
			Bundle savedInstanceState)
	{
		View view = inflater.inflate(R.layout.activity_factura, container, false);

        //Set data to view

	    return view;
	}
}

At the moment, when I click on list item, white view appears in first page. I've verified and onCreateView method of "DetallesFacturaFragment" is executed, but nothing appears on that page.

And first time I click on list item, it shows that white screen. But after coming back to list, I have to click twice to a list item for showing white screen.

I've been googling and looking at some many questions but couldn't find anyone solved with completed code.

After so many hours spent, I've found correct solution modifying code in that answer.

It replaces Fragment in first page of ViewPager with another one, and if you return back from second Fragment, first Fragment is correctly displayed. Doesn't matter Fragment displayed in first page, if you swipe from one page to another, it doesn't change its Fragment.

Here is my code:

FragmentActivity

public class TabsFacturasActivity extends SherlockFragmentActivity {

    public void onBackPressed() {
		if(mPager.getCurrentItem() == 0) {
			if (mAdapter.getItem(0) instanceof DetallesFacturaFragment) {
				((DetallesFacturaFragment) mAdapter.getItem(0)).backPressed();
			}
			else if (mAdapter.getItem(0) instanceof FacturasFragment) {
				finish();
			}
		}
	}
	
	private static class MyAdapter extends FragmentPagerAdapter {
		
		private final class FirstPageListener implements
		FirstPageFragmentListener {
			public void onSwitchToNextFragment() {
				mFragmentManager.beginTransaction().remove(mFragmentAtPos0)
				.commit();
				if (mFragmentAtPos0 instanceof FacturasFragment){
					mFragmentAtPos0 = new DetallesFacturaFragment(listener);
				}else{ // Instance of NextFragment
					mFragmentAtPos0 = new FacturasFragment(listener);
				}
				notifyDataSetChanged();
			}
		}

		private String[] titles = { "VER FACTURAS", "VER CONSUMO", "INTRODUCIR LECTURA" };
	    private final FragmentManager mFragmentManager;
	    public Fragment mFragmentAtPos0;
	    private Context context;
	    FirstPageListener listener = new FirstPageListener();

		public MyAdapter(FragmentManager fragmentManager) {
			super(fragmentManager);
			mFragmentManager = fragmentManager;
		}

		@Override
		public CharSequence getPageTitle(int position) {
			return titles[position];
		}

		@Override
		public Fragment getItem(int position) {
			switch (position) {
	        case 0: // Fragment # 0
	        	if (mFragmentAtPos0 == null)
	            {
	                mFragmentAtPos0 = new FacturasFragment(listener);
	            }
	            return mFragmentAtPos0;

	        case 1: // Fragment # 1
	            return new ConsumoFragment();
	        case 2:// Fragment # 2
	            return new LecturaFragment();
	        }
			return null;
		}

		@Override
		public int getCount() {
			return titles.length;
		}
		
		@Override
		public int getItemPosition(Object object)
		{
			if (object instanceof FacturasFragment && 
					mFragmentAtPos0 instanceof DetallesFacturaFragment) {
				return POSITION_NONE;
			}
			if (object instanceof DetallesFacturaFragment && 
					mFragmentAtPos0 instanceof FacturasFragment) {
				return POSITION_NONE;
			}
			return POSITION_UNCHANGED;
		}

	}

}

FirstPageFragmentListener

public interface FirstPageFragmentListener {
    void onSwitchToNextFragment();
}

FacturasFragment (FirstFragment)

public class FacturasFragment extends ListFragment implements FirstPageFragmentListener {
	
	static FirstPageFragmentListener firstPageListener;
	
	public FacturasFragment() {
	}

	public FacturasFragment(FirstPageFragmentListener listener) {
		firstPageListener = listener;
	}

    public void onListItemClick (ListView l, View v, int position, long id) {
        firstPageListener.onSwitchToNextFragment();
    }
}

DetallesFacturaFragment (SecondFragment)

public class DetallesFacturaFragment extends SherlockFragment {
    	
	static FirstPageFragmentListener firstPageListener;
	
	public DetallesFacturaFragment() {
	}
	
	public DetallesFacturaFragment(FirstPageFragmentListener listener) {
		firstPageListener = listener;
	}

	public void backPressed() {
		firstPageListener.onSwitchToNextFragment();
	}
}

To solve minor issue that Android suggest not using non-default constructor for fragment. You should change the constructor to something like this:

in FacturasFragment :

 public static FacturasFragment createInstance(FirstPageFragmentListener listener) {
    FacturasFragment facturasFragment = new FacturasFragment(); 
    facturasFragment.firstPageListener = listener;
    return facturasFragment;
 }

Then you can call it from getItem function like this :

 mFragmentAtPos0 = FacturasFragment.createInstance(listener);

in DetallesFacturaFragment :

 public static DetallesFacturaFragment createInstance(FirstPageFragmentListener listener) {
    DetallesFacturaFragment detallesFacturaFragment= new DetallesFacturaFragment(); 
    detallesFacturaFragment.firstPageListener = listener;
    return detallesFacturaFragment;
 }

Then you can call it from FirstPageListener.onSwitchToNextFragment() function like this :

 mFragmentAtPos0 = DetallesFacturaFragment.createInstance(listener);

I found two ways to replace fragment in viewpager.

Way 1: By updating ViewPagerAdapter Way 2: By using a root fragment

Way1: In this way, we need to update the fragment from viewpager adapter's fragment list and notify the fragment about the change. For example:

  private void changefragment(int position) {
        Fragment newFragment = CategoryPostFragment.newInstance();
        adapter.fragments.set(position, newFragment);
        adapter.notifyDataSetChanged();
        viewPager.setCurrentItem(position);

    }

Here is the viewpager adapter code for this

import java.util.List;
import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;
import androidx.fragment.app.FragmentStatePagerAdapter;
import androidx.viewpager.widget.PagerAdapter;

import com.trickbd.trickbdapp.ui.activity.homeactivity.fragments.FavFragment;
import com.trickbd.trickbdapp.ui.activity.homeactivity.fragments.HomePostFragment;

public class ViewPagerAdapter extends FragmentStatePagerAdapter {
    public List<Fragment> fragments;

    public ViewPagerAdapter(FragmentManager manager, List<Fragment> fragments) {
        super(manager);
        this.fragments = fragments;
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {
        if (fragments.get(position)!=null){
            return fragments.get(position);
        }else {
            if (position==0){
                return new HomePostFragment();
            }else {
                return new FavFragment();
            }
        }

    }

    @Override
    public int getCount() {
        return fragments.size();
    }

    //method to add fragment
    public void addFragment(Fragment fragment) {
        fragments.add(fragment);
    }


    @Override
    public int getItemPosition(@NonNull Object object) {
        if (object instanceof FavFragment) {
            return POSITION_UNCHANGED; // don't force a reload
        } else {
            // POSITION_NONE means something like: this fragment is no longer valid
            // triggering the ViewPager to re-build the instance of this fragment.
            return POSITION_NONE;
        }
    }

}

I was doing fine with this code. I become concerned when the super(manager) method of FragmentStatePagerAdapter deprecated in api 28. When I use "super(manager,BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);" along with first way of replacing fragment the application crash on runtime.

Also, there is a back draw that when we called adapter.notifydatasetchanged() from the viewpager adapter it's not efficient. It's recreating the whole viewpager while we are trying to change only a specific fragment.

So, way no 2 come with the solution of all problems.

Way 2: Without adding the actual fragment to the viewpager we should add a root fragment to the viewpager. In root fragment there will be actual fragment added(previously we added in the viewpager. Then we can replace any fragment easily without the help of FragmentStatePagerAdapter. Code of the root fragment:

Rootfragment.java

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.fragment.app.FragmentTransaction;

import com.trickbd.trickbdapp.R;

import dagger.android.support.DaggerFragment;

public class RootFragment extends DaggerFragment {
    public RootFragment() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }


    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.root_layout, container, false);
        if (getFragmentManager() != null) {
            FragmentTransaction transaction = getFragmentManager()
                    .beginTransaction();
            transaction.replace(R.id.root_frame, new HomePostFragment());

            transaction.commit();
        }

        return view;

    }
}

root_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/root_frame">

</FrameLayout>

So previous replacing code will be updated like below

private void changefragment(int position) {
        Fragment newFragment = CategoryPostFragment.newInstance();
        replacefragment(newFragment);
        viewPager.setCurrentItem(position);

    }

public void replacefragment(Fragment fragment){
        getSupportFragmentManager();
        FragmentTransaction trans = getSupportFragmentManager()
                .beginTransaction();
        trans.replace(R.id.root_frame, fragment);
        trans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        trans.addToBackStack(null);
        trans.commit();
    }

By this way, we can replace the fragment more efficiently.

To get the currently added fragment in rootfragment we may use this code.

if (getSupportFragmentManager().findFragmentById(R.id.root_frame) instanceof HomePostFragment){
            HomePostFragment postFragment = (HomePostFragment) getSupportFragmentManager().findFragmentById(R.id.root_frame);
            
 }

You may learn more about this here