dynamically add and remove view to viewpager

(I figured out a solution - please see my post in the Answer section below.)

In my app, the user will start with a single view of his data. I'd like to add a ViewPager and allow the user to add more views as desired. How do I do this? (I dont' want to use the FragmentPagerAdapter.)

I've read countless posts and overviews but am still missing something. Here's what I think I understand:

MainActivity creates a ViewPager and PagerAdapter:

ViewPager pager = null;
MainPagerAdapter adapter = null;
public void onCreate (Bundle savedInstanceState)
{
  super.onCreate (savedInstanceState);
  pager = new ViewPager (this);
  setContentView (pager);

  adapter = new MainPagerAdapter();
  pager.setAdapter (adapter); 

  View v0 = code_to_create_initial_view();
  adapter.add (v0, 0);      
}

Use a PagerAdapter to provide the sets of view. For this it seems I need methods to add and remove views, something like this; obviously more is needed to tell the ViewPager stuff has changed and how to show the change:

class MainPagerAdapter extends PagerAdapter
{
  // This holds all the currently displayable views, in order from left to right.
  private ArrayList<View> views = new ArrayList<View>();

  public void addView (View v, int position)
  {
    views.add (position, v);
  }

  public void removeView (int position)
  {
    views.remove (position);
  }
}

In addition, I need to implement the following vitual methods. I'm lost here - what calls them and what are they supposed to do (ok, getCount is obvious)?

  public object instantiateItem (ViewGroup pager, int position);
  public void destroyItem (ViewGroup, int, Object);
  public int getCount ();
  public boolean isViewFromObject (View, Object);

• What are the ViewGroup params for - isn't the containing group the ViewPager itself?
• What does isViewFromObject do - how does an object get associated with a view in the first place?
• Should I be calling startUpdate and finishUdate when I add or remove views?

Thanks.

After figuring out which ViewPager methods are called by ViewPager and which are for other purposes, I came up with a solution. I present it here since I see a lot of people have struggled with this and I didn't see any other relevant answers.

First, here's my adapter; hopefully comments within the code are sufficient:

public class MainPagerAdapter extends PagerAdapter
{
  // This holds all the currently displayable views, in order from left to right.
  private ArrayList<View> views = new ArrayList<View>();

  //-----------------------------------------------------------------------------
  // Used by ViewPager.  "Object" represents the page; tell the ViewPager where the
  // page should be displayed, from left-to-right.  If the page no longer exists,
  // return POSITION_NONE.
  @Override
  public int getItemPosition (Object object)
  {
    int index = views.indexOf (object);
    if (index == -1)
      return POSITION_NONE;
    else
      return index;
  }

  //-----------------------------------------------------------------------------
  // Used by ViewPager.  Called when ViewPager needs a page to display; it is our job
  // to add the page to the container, which is normally the ViewPager itself.  Since
  // all our pages are persistent, we simply retrieve it from our "views" ArrayList.
  @Override
  public Object instantiateItem (ViewGroup container, int position)
  {
    View v = views.get (position);
    container.addView (v);
    return v;
  }

  //-----------------------------------------------------------------------------
  // Used by ViewPager.  Called when ViewPager no longer needs a page to display; it
  // is our job to remove the page from the container, which is normally the
  // ViewPager itself.  Since all our pages are persistent, we do nothing to the
  // contents of our "views" ArrayList.
  @Override
  public void destroyItem (ViewGroup container, int position, Object object)
  {
    container.removeView (views.get (position));
  }

  //-----------------------------------------------------------------------------
  // Used by ViewPager; can be used by app as well.
  // Returns the total number of pages that the ViewPage can display.  This must
  // never be 0.
  @Override
  public int getCount ()
  {
    return views.size();
  }

  //-----------------------------------------------------------------------------
  // Used by ViewPager.
  @Override
  public boolean isViewFromObject (View view, Object object)
  {
    return view == object;
  }

  //-----------------------------------------------------------------------------
  // Add "view" to right end of "views".
  // Returns the position of the new view.
  // The app should call this to add pages; not used by ViewPager.
  public int addView (View v)
  {
    return addView (v, views.size());
  }

  //-----------------------------------------------------------------------------
  // Add "view" at "position" to "views".
  // Returns position of new view.
  // The app should call this to add pages; not used by ViewPager.
  public int addView (View v, int position)
  {
    views.add (position, v);
    return position;
  }

  //-----------------------------------------------------------------------------
  // Removes "view" from "views".
  // Retuns position of removed view.
  // The app should call this to remove pages; not used by ViewPager.
  public int removeView (ViewPager pager, View v)
  {
    return removeView (pager, views.indexOf (v));
  }

  //-----------------------------------------------------------------------------
  // Removes the "view" at "position" from "views".
  // Retuns position of removed view.
  // The app should call this to remove pages; not used by ViewPager.
  public int removeView (ViewPager pager, int position)
  {
    // ViewPager doesn't have a delete method; the closest is to set the adapter
    // again.  When doing so, it deletes all its views.  Then we can delete the view
    // from from the adapter and finally set the adapter to the pager again.  Note
    // that we set the adapter to null before removing the view from "views" - that's
    // because while ViewPager deletes all its views, it will call destroyItem which
    // will in turn cause a null pointer ref.
    pager.setAdapter (null);
    views.remove (position);
    pager.setAdapter (this);

    return position;
  }

  //-----------------------------------------------------------------------------
  // Returns the "view" at "position".
  // The app should call this to retrieve a view; not used by ViewPager.
  public View getView (int position)
  {
    return views.get (position);
  }

  // Other relevant methods:

  // finishUpdate - called by the ViewPager - we don't care about what pages the
  // pager is displaying so we don't use this method.
}

And here's some snips of code showing how to use the adapter.

class MainActivity extends Activity
{
  private ViewPager pager = null;
  private MainPagerAdapter pagerAdapter = null;

  //-----------------------------------------------------------------------------
  @Override
  public void onCreate (Bundle savedInstanceState)
  {
    super.onCreate(savedInstanceState);
    setContentView (R.layout.main_activity);

    ... do other initialization, such as create an ActionBar ...
    
    pagerAdapter = new MainPagerAdapter();
    pager = (ViewPager) findViewById (R.id.view_pager);
    pager.setAdapter (pagerAdapter);

    // Create an initial view to display; must be a subclass of FrameLayout.
    LayoutInflater inflater = context.getLayoutInflater();
    FrameLayout v0 = (FrameLayout) inflater.inflate (R.layout.one_of_my_page_layouts, null);
    pagerAdapter.addView (v0, 0);
    pagerAdapter.notifyDataSetChanged();
  }

  //-----------------------------------------------------------------------------
  // Here's what the app should do to add a view to the ViewPager.
  public void addView (View newPage)
  {
    int pageIndex = pagerAdapter.addView (newPage);
    // You might want to make "newPage" the currently displayed page:
    pager.setCurrentItem (pageIndex, true);
  }

  //-----------------------------------------------------------------------------
  // Here's what the app should do to remove a view from the ViewPager.
  public void removeView (View defunctPage)
  {
    int pageIndex = pagerAdapter.removeView (pager, defunctPage);
    // You might want to choose what page to display, if the current page was "defunctPage".
    if (pageIndex == pagerAdapter.getCount())
      pageIndex--;
    pager.setCurrentItem (pageIndex);
  }

  //-----------------------------------------------------------------------------
  // Here's what the app should do to get the currently displayed page.
  public View getCurrentPage ()
  {
    return pagerAdapter.getView (pager.getCurrentItem());
  }

  //-----------------------------------------------------------------------------
  // Here's what the app should do to set the currently displayed page.  "pageToShow" must
  // currently be in the adapter, or this will crash.
  public void setCurrentPage (View pageToShow)
  {
    pager.setCurrentItem (pagerAdapter.getItemPosition (pageToShow), true);
  }
}

Finally, you can use the following for your activity_main.xml layout:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.view.ViewPager
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/view_pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

</android.support.v4.view.ViewPager>

I was looking for simple solution to remove views from viewpager (no fragments) dynamically. So, if you have some info, that your pages belongs to, you can set it to View as tag. Just like that (adapter code):

@Override
public Object instantiateItem(ViewGroup collection, int position)
{
    ImageView iv = new ImageView(mContext);
    MediaMessage msg = mMessages.get(position);
    ...

    iv.setTag(media);
    return iv;
}

@Override
public int getItemPosition (Object object)
{
    View o = (View) object;
    int index = mMessages.indexOf(o.getTag());
    if (index == -1)
        return POSITION_NONE;
    else
        return index;
}

You just need remove your info from mMessages, and then call notifyDataSetChanged() for your adapter. Bad news there is no animation in this case.

Here's an alternative solution to this question. My adapter:

    private class PagerAdapter extends FragmentPagerAdapter implements 
    				ViewPager.OnPageChangeListener, TabListener {

	private List<Fragment> mFragments = new ArrayList<Fragment>();
	private ViewPager mPager;
	private ActionBar mActionBar;
	
	private Fragment mPrimaryItem;

	public PagerAdapter(FragmentManager fm, ViewPager vp, ActionBar ab) {
		super(fm);
		mPager = vp;
		mPager.setAdapter(this);
		mPager.setOnPageChangeListener(this);
		mActionBar = ab;
	}

	public void addTab(PartListFragment frag) {
		mFragments.add(frag);
		mActionBar.addTab(mActionBar.newTab().setTabListener(this).
							setText(frag.getPartCategory()));
	}

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

	@Override
	public int getCount() {
		return mFragments.size();
	}
	
	/** (non-Javadoc)
	 * @see android.support.v4.app.FragmentStatePagerAdapter#setPrimaryItem(android.view.ViewGroup, int, java.lang.Object)
	 */
	@Override
	public void setPrimaryItem(ViewGroup container, int position,
			Object object) {
		super.setPrimaryItem(container, position, object);
        mPrimaryItem = (Fragment) object;
	}
	
	/** (non-Javadoc)
	 * @see android.support.v4.view.PagerAdapter#getItemPosition(java.lang.Object)
	 */
	@Override
	public int getItemPosition(Object object) {
        if (object == mPrimaryItem) {
            return POSITION_UNCHANGED;
        }
        return POSITION_NONE;
	}

	@Override
	public void onTabSelected(Tab tab, FragmentTransaction ft) {
		mPager.setCurrentItem(tab.getPosition());
	}

	@Override
	public void onTabUnselected(Tab tab, FragmentTransaction ft) { }

	@Override
	public void onTabReselected(Tab tab, FragmentTransaction ft) { }

	@Override
	public void onPageScrollStateChanged(int arg0) { }

	@Override
	public void onPageScrolled(int arg0, float arg1, int arg2) { }

	@Override
	public void onPageSelected(int position) {
		mActionBar.setSelectedNavigationItem(position);
	}

	/**
	 * This method removes the pages from ViewPager
	 */
	public void removePages() {
		mActionBar.removeAllTabs();
                    
                    //call to ViewPage to remove the pages
		vp.removeAllViews();
		mFragments.clear();
		
		//make this to update the pager
		vp.setAdapter(null);
		vp.setAdapter(pagerAdapter);
	}
}

Code to remove and add dynamically

//remove the pages. basically call to method removeAllViews from `ViewPager`
pagerAdapter.removePages();

pagerAdapter.addPage(pass your fragment);

After the advice of Peri Hartman, it started to work after I set null do ViewPager adapter and put the adapter again after the views removed. Before this the page 0 doesnt showed its list contents.

Thanks.

There are quite a few discussions around this topic

• ViewPager PagerAdapter not updating the View
• Update ViewPager dynamically?
• Removing fragments from FragmentStatePagerAdapter

Although we see it often, using POSITION_NONE does not seem to be the way to go as it is very inefficient memory-wise.

Here in this question, we should consider using Alvaro's approach:

> ... is to setTag() method in > instantiateItem() when instantiating a new view. Then instead of using > notifyDataSetChanged(), you can use findViewWithTag() to find the view > you want to update.

Here is a SO answer with code based on this idea

I did a similar program. hope this would help you.In its first activity four grid data can be selected. On the next activity, there is a view pager which contains two mandatory pages.And 4 more pages will be there, which will be visible corresponding to the grid data selected.

Following is the mainactivty MainActivity

    package com.example.jeffy.viewpagerapp;
    import android.content.Context;
    import android.content.Intent;
    import android.content.SharedPreferences;
    import android.database.Cursor;
    import android.database.SQLException;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteOpenHelper;
    import android.os.Bundle;
    import android.os.Parcel;
    import android.support.design.widget.FloatingActionButton;
    import android.support.design.widget.Snackbar;
    import android.support.v7.app.AppCompatActivity;
    import android.support.v7.widget.Toolbar;
    import android.util.Log;
    import android.view.View;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.widget.AdapterView;
    import android.widget.Button;
    import android.widget.GridView;
    import java.lang.reflect.Array;
    import java.util.ArrayList;
    public class MainActivity extends AppCompatActivity {
    SharedPreferences pref;
    SharedPreferences.Editor editor;
    GridView gridView;
    Button button;
    private static final String DATABASE_NAME = "dbForTest.db";
    private static final int DATABASE_VERSION = 1;
    private static final String TABLE_NAME = "diary";
    private static final String TITLE = "id";
    private static final String BODY = "content";
    DBHelper  dbHelper = new DBHelper(this);
    ArrayList<String> frags = new ArrayList<String>();
    ArrayList<FragmentArray> fragmentArray = new ArrayList<FragmentArray>();
    String[] selectedData;
    Boolean port1=false,port2=false,port3=false,port4=false;
    int Iport1=1,Iport2=1,Iport3=1,Iport4=1,location;



    // This Data show in grid ( Used by adapter )
        CustomGridAdapter customGridAdapter = new           CustomGridAdapter(MainActivity.this,GRID_DATA);
    static final String[ ] GRID_DATA = new String[] {
            "1" ,
            "2",
            "3" ,
            "4"
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        frags.add("TabFragment3");
        frags.add("TabFragment4");
        frags.add("TabFragment5");
        frags.add("TabFragment6");
        dbHelper = new DBHelper(this);
        dbHelper.insertContact(1,0);
        dbHelper.insertContact(2,0);
        dbHelper.insertContact(3,0);
        dbHelper.insertContact(4,0);
        final Bundle selected = new Bundle();
        button = (Button) findViewById(R.id.button);
        pref = getApplicationContext().getSharedPreferences("MyPref", MODE_PRIVATE);
        editor = pref.edit();
        gridView = (GridView) findViewById(R.id.gridView1);

        gridView.setAdapter(customGridAdapter);

        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
              //view.findViewById(R.id.grid_item_image).setVisibility(View.VISIBLE);
                location = position + 1;
                if (position == 0) {
                    Iport1++;
                    Iport1 = Iport1 % 2;
                    if (Iport1 % 2 == 1) {
                        //dbHelper.updateContact(1,1);
                        view.findViewById(R.id.grid_item_image).setVisibility(View.VISIBLE);
                        dbHelper.updateContact(1,1);
                    } else {
                        //dbHelper.updateContact(1,0);
                        view.findViewById(R.id.grid_item_image).setVisibility(View.INVISIBLE);
                        dbHelper.updateContact(1, 0);
                    }
                }
                if (position == 1) {
                    Iport2++;
                    Iport1 = Iport1 % 2;
                    if (Iport2 % 2 == 1) {
                        //dbHelper.updateContact(2,1);
                        view.findViewById(R.id.grid_item_image).setVisibility(View.VISIBLE);
                        dbHelper.updateContact(2, 1);
                    } else {
                        //dbHelper.updateContact(2,0);
                        view.findViewById(R.id.grid_item_image).setVisibility(View.INVISIBLE);
                        dbHelper.updateContact(2,0);
                    }
                }
                if (position == 2) {
                    Iport3++;
                    Iport3 = Iport3 % 2;
                    if (Iport3 % 2 == 1) {
                        //dbHelper.updateContact(3,1);
                        view.findViewById(R.id.grid_item_image).setVisibility(View.VISIBLE);
                        dbHelper.updateContact(3, 1);
                    } else {
                        //dbHelper.updateContact(3,0);
                        view.findViewById(R.id.grid_item_image).setVisibility(View.INVISIBLE);
                        dbHelper.updateContact(3, 0);
                    }
                }
                if (position == 3) {
                    Iport4++;
                    Iport4 = Iport4 % 2;
                    if (Iport4 % 2 == 1) {
                        //dbHelper.updateContact(4,1);
                       view.findViewById(R.id.grid_item_image).setVisibility(View.VISIBLE);
                        dbHelper.updateContact(4, 1);
                    } else {
                        //dbHelper.updateContact(4,0);
                       view.findViewById(R.id.grid_item_image).setVisibility(View.INVISIBLE);
                        dbHelper.updateContact(4,0);
                    }
                }
            }
        });
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                editor.putInt("port1", Iport1);
                editor.putInt("port2", Iport2);
                editor.putInt("port3", Iport3);
                editor.putInt("port4", Iport4);
                Intent i = new Intent(MainActivity.this,Main2Activity.class);
                if(Iport1==1)
                    i.putExtra("3","TabFragment3");
                else
                    i.putExtra("3", "");
                if(Iport2==1)
                    i.putExtra("4","TabFragment4");
                else
                    i.putExtra("4","");
                if(Iport3==1)
                    i.putExtra("5", "TabFragment5");
                else
                    i.putExtra("5","");
                if(Iport4==1)
                    i.putExtra("6", "TabFragment6");
                else
                    i.putExtra("6","");
                dbHelper.updateContact(0, Iport1);
                dbHelper.updateContact(1, Iport2);
                dbHelper.updateContact(2, Iport3);
                dbHelper.updateContact(3, Iport4);
                startActivity(i);
            }
        });
    }
}

Here TabFragment1,TabFragment2 etc are fragment to be displayed on the viewpager.And I am not showing the layouts since they are out of scope of this project.

MainActivity will intent to Main2Activity Main2Activity

    package com.example.jeffy.viewpagerapp;

import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.support.design.widget.CollapsingToolbarLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.NestedScrollView;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.text.TextUtils;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.FrameLayout;

import java.util.ArrayList;

public class Main2Activity extends AppCompatActivity {

    private ViewPager pager = null;
    private PagerAdapter pagerAdapter = null;
    DBHelper dbHelper;
    Cursor rs;
    int port1,port2,port3,port4;
    //-----------------------------------------------------------------------------
    @Override
    public void onCreate (Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        Toolbar toolbar = (Toolbar) findViewById(R.id.MyToolbar);
        setSupportActionBar(toolbar);

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        CollapsingToolbarLayout collapsingToolbar =
                (CollapsingToolbarLayout) findViewById(R.id.collapse_toolbar);


        NestedScrollView scrollView = (NestedScrollView) findViewById (R.id.nested);
        scrollView.setFillViewport (true);

        ArrayList<String > selectedPort = new ArrayList<String>();

        Intent intent = getIntent();
        String Tab3 = intent.getStringExtra("3");
        String Tab4 = intent.getStringExtra("4");
        String Tab5 = intent.getStringExtra("5");
        String Tab6 = intent.getStringExtra("6");

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
        tabLayout.addTab(tabLayout.newTab().setText("View"));
        tabLayout.addTab(tabLayout.newTab().setText("All"));

        selectedPort.add("TabFragment1");
        selectedPort.add("TabFragment2");
        if(Tab3!=null && !TextUtils.isEmpty(Tab3))
        selectedPort.add(Tab3);
        if(Tab4!=null && !TextUtils.isEmpty(Tab4))
        selectedPort.add(Tab4);
        if(Tab5!=null && !TextUtils.isEmpty(Tab5))
        selectedPort.add(Tab5);
        if(Tab6!=null && !TextUtils.isEmpty(Tab6))
        selectedPort.add(Tab6);



        dbHelper = new DBHelper(this);
//        rs=dbHelper.getData(1);
//        port1 = rs.getInt(rs.getColumnIndex("id"));
//
//        rs=dbHelper.getData(2);
//        port2 = rs.getInt(rs.getColumnIndex("id"));
//
//        rs=dbHelper.getData(3);
//        port3 = rs.getInt(rs.getColumnIndex("id"));
//
//        rs=dbHelper.getData(4);
//        port4 = rs.getInt(rs.getColumnIndex("id"));


        Log.i(">>>>>>>>>>>>>>", "port 1" + port1 + "port 2" + port2 + "port 3" + port3 + "port 4" + port4);

        if(Tab3!=null && !TextUtils.isEmpty(Tab3))
        tabLayout.addTab(tabLayout.newTab().setText("Tab 0"));
        if(Tab3!=null && !TextUtils.isEmpty(Tab4))
        tabLayout.addTab(tabLayout.newTab().setText("Tab 1"));
        if(Tab3!=null && !TextUtils.isEmpty(Tab5))
        tabLayout.addTab(tabLayout.newTab().setText("Tab 2"));
        if(Tab3!=null && !TextUtils.isEmpty(Tab6))
        tabLayout.addTab(tabLayout.newTab().setText("Tab 3"));
        tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

        final ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
        final PagerAdapter adapter = new PagerAdapter
                (getSupportFragmentManager(), tabLayout.getTabCount(), selectedPort);
        viewPager.setAdapter(adapter);
        viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
        tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                viewPager.setCurrentItem(tab.getPosition());
            }

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

            }

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

            }
        });
//        setContentView(R.layout.activity_main2);
//        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
//        setSupportActionBar(toolbar);

//        TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
//        tabLayout.addTab(tabLayout.newTab().setText("View"));
//        tabLayout.addTab(tabLayout.newTab().setText("All"));
//        tabLayout.addTab(tabLayout.newTab().setText("Tab 0"));
//        tabLayout.addTab(tabLayout.newTab().setText("Tab 1"));
//        tabLayout.addTab(tabLayout.newTab().setText("Tab 2"));
//        tabLayout.addTab(tabLayout.newTab().setText("Tab 3"));
//        tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);


}
    }

ViewPagerAdapter Viewpageradapter.class

package com.example.jeffy.viewpagerapp;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.ViewGroup;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Jeffy on 25-01-2016.
 */
public class PagerAdapter extends FragmentStatePagerAdapter {
    int mNumOfTabs;

    List<String> values;

    public PagerAdapter(FragmentManager fm, int NumOfTabs, List<String> Port) {
        super(fm);
        this.mNumOfTabs = NumOfTabs;
        this.values= Port;
    }


    @Override
    public Fragment getItem(int position) {


        String fragmentName = values.get(position);
        Class<?> clazz = null;
        Object fragment = null;
        try {
            clazz = Class.forName("com.example.jeffy.viewpagerapp."+fragmentName);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        try {
            fragment = clazz.newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

        return (Fragment) fragment;
    }

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

Layout for main2activity acticity_main2.xml

    <android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/main_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true">
    
        <android.support.design.widget.AppBarLayout
            android:id="@+id/MyAppbar"
            android:layout_width="match_parent"
            android:layout_height="256dp"
            android:fitsSystemWindows="true">
    
            <android.support.design.widget.CollapsingToolbarLayout
                android:id="@+id/collapse_toolbar"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                app:layout_scrollFlags="scroll|exitUntilCollapsed"
                android:background="@color/material_deep_teal_500"
                android:fitsSystemWindows="true">
    
                <ImageView
                    android:id="@+id/bgheader"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:scaleType="centerCrop"
                    android:fitsSystemWindows="true"
                    android:background="@drawable/screen"
                    app:layout_collapseMode="pin" />
    
                <android.support.v7.widget.Toolbar
                    android:id="@+id/MyToolbar"
                    android:layout_width="match_parent"
                    android:layout_height="?attr/actionBarSize"
                    app:layout_collapseMode="parallax" />
    
    
    
    
    
            </android.support.design.widget.CollapsingToolbarLayout>
    
        </android.support.design.widget.AppBarLayout>
    
        <android.support.v4.widget.NestedScrollView
            android:layout_width="match_parent"
            android:id="@+id/nested"
            android:layout_height="match_parent"
            android:layout_gravity="fill_vertical"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">
    
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <android.support.design.widget.TabLayout
            android:id="@+id/tab_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@+id/MyToolbar"
            android:background="?attr/colorPrimary"
            android:elevation="6dp"
            android:minHeight="?attr/actionBarSize"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"/>
    
    
        <android.support.v4.view.ViewPager
            xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/view_pager"
            android:layout_width="match_parent"
            android:layout_height="match_parent" >
    
        </android.support.v4.view.ViewPager>
    </LinearLayout>
    
    
        </android.support.v4.widget.NestedScrollView>
    
    </android.support.design.widget.CoordinatorLayout>

Mainactivity layout
activity_main.xml

        <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.example.jeffy.viewpagerapp.MainActivity"
    tools:showIn="@layout/activity_main">


<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <GridView xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/gridView1"
        android:numColumns="2"
        android:gravity="center"
        android:columnWidth="100dp"
        android:stretchMode="columnWidth"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >

    </GridView>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="SAVE"
        android:id="@+id/button" />

</LinearLayout>




</RelativeLayout>

Hope this would help someone... Click up button please if this helped you

I've created a custom PagerAdapters library to change items in PagerAdapters dynamically.

You can change items dynamically like following by using this library.

@Override
protected void onCreate(Bundle savedInstanceState) {
        /** ... **/
    adapter = new MyStatePagerAdapter(getSupportFragmentManager()
                            , new String[]{"1", "2", "3"});
    ((ViewPager)findViewById(R.id.view_pager)).setAdapter(adapter);
     adapter.add("4");
     adapter.remove(0);
}

class MyPagerAdapter extends ArrayViewPagerAdapter<String> {

    public MyPagerAdapter(String[] data) {
        super(data);
    }

    @Override
    public View getView(LayoutInflater inflater, ViewGroup container, String item, int position) {
        View v = inflater.inflate(R.layout.item_page, container, false);
        ((TextView) v.findViewById(R.id.item_txt)).setText(item);
        return v;
    }
}

Thils library also support pages created by Fragments.

To remove you can use this directly:

getSupportFragmentManager().beginTransaction().remove(fragment).
                            commitAllowingStateLoss();

fragment is the fragment you want to remove.

I find a good solution for this issue, this solution can make it work and no need to recreate Fragments.
My key point is:

1. setup ViewPager every time you delete or add Tab(Fragment).
2. Override the getItemId method, return a specific id rather than position.

Source Code

package com.zq.testviewpager;

import android.support.annotation.Nullable;
import android.support.design.widget.TabLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

import android.widget.TextView;

import java.util.ArrayList;
import java.util.Arrays;
/**
 * Created by [email protected] on 2017/5/31.
 * Implement dynamic delete or add tab(TAB_C in this test code).
 */
public class MainActivity extends AppCompatActivity {

    private static final int TAB_A = 1001;
    private static final int TAB_B = 1002;
    private static final int TAB_C = 1003;
    private static final int TAB_D = 1004;
    private static final int TAB_E = 1005;
    private Tab[] tabsArray = new Tab[]{new Tab(TAB_A, "A"),new Tab(TAB_B, "B"),new Tab(TAB_C, "C"),new Tab(TAB_D, "D"),new Tab(TAB_E, "E")};

    private ArrayList<Tab> mTabs = new ArrayList<>(Arrays.asList(tabsArray));

    private Tab[] tabsArray2 = new Tab[]{new Tab(TAB_A, "A"),new Tab(TAB_B, "B"),new Tab(TAB_D, "D"),new Tab(TAB_E, "E")};

    private ArrayList<Tab> mTabs2 = new ArrayList<>(Arrays.asList(tabsArray2));

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link FragmentPagerAdapter} derivative, which will keep every
     * loaded fragment in memory. If this becomes too memory intensive, it
     * may be best to switch to a
     * {@link android.support.v4.app.FragmentStatePagerAdapter}.
     */
    private SectionsPagerAdapter mSectionsPagerAdapter;

    /**
     * The {@link ViewPager} that will host the section contents.
     */
    private ViewPager mViewPager;
    private TabLayout tabLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(mTabs, getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.container);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(mViewPager);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }else if (id == R.id.action_delete) {
            int currentItemPosition = mViewPager.getCurrentItem();
            Tab currentTab = mTabs.get(currentItemPosition);

            if(currentTab.id == TAB_C){
                currentTab = mTabs.get(currentItemPosition == 0 ? currentItemPosition +1 : currentItemPosition - 1);
            }

            mSectionsPagerAdapter = new SectionsPagerAdapter(mTabs2, getSupportFragmentManager());
            mViewPager.setAdapter(mSectionsPagerAdapter);
            tabLayout.setupWithViewPager(mViewPager);


            mViewPager.setCurrentItem(mTabs2.indexOf(currentTab), false);
            return true;
        }else if (id == R.id.action_add) {

            int currentItemPosition = mViewPager.getCurrentItem();
            Tab currentTab = mTabs2.get(currentItemPosition);

            mSectionsPagerAdapter = new SectionsPagerAdapter(mTabs, getSupportFragmentManager());
            mViewPager.setAdapter(mSectionsPagerAdapter);
            tabLayout.setupWithViewPager(mViewPager);

            mViewPager.setCurrentItem(mTabs.indexOf(currentTab), false);
            return true;
        }else

        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        public PlaceholderFragment() {
        }

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            Log.e("TestViewPager", "onCreate"+getArguments().getInt(ARG_SECTION_NUMBER));
        }

        @Override
        public void onDestroy() {
            super.onDestroy();
            Log.e("TestViewPager", "onDestroy"+getArguments().getInt(ARG_SECTION_NUMBER));
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            TextView textView = (TextView) rootView.findViewById(R.id.section_label);
            textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER)));
            return rootView;
        }
    }

    /**
     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
     * one of the sections/tabs/pages.
     */
    public class SectionsPagerAdapter extends FragmentPagerAdapter {
        ArrayList<Tab> tabs;

        public SectionsPagerAdapter(ArrayList<Tab> tabs, FragmentManager fm) {
            super(fm);
            this.tabs = tabs;
        }

        @Override
        public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a PlaceholderFragment (defined as a static inner class below).
            return PlaceholderFragment.newInstance(tabs.get(position).id);
        }

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

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

        @Override
        public CharSequence getPageTitle(int position) {
            return tabs.get(position).title;
        }
    }

    private static class Tab {
        String title;
        public int id;

        Tab(int id, String title){
            this.id = id;
            this.title = title;
        }

        @Override
        public boolean equals(Object obj) {
            if(obj instanceof Tab){
                return ((Tab)obj).id == id;
            }else{
                return false;
            }
        }
    }
}

Code is at my Github Gist.