Changing ViewPager to enable infinite page scrolling

Question

Jon Willis has posted on how to enable an infinite scrolling with his code  In there he said that he made some changes in the ViewPager class int the android support library  Which changes have been made and how is it possible to  recompile  the library with the ViewPager change

User · Answer

infinite slider adapter skeleton based on previous samples

some critical issues:

remember original (relative) position in page view (tag used in sample), so we will look this position to define relative position of view. otherwise child order in pager is mixed
have to fill first time absolute view inside adapter. (the rest of times this fill will be invalid) found no way to force it fill from pager handler. the rest times absolute view will be overriden from pager handler with correct values.
when pages are slided quickly, side page (actually left) is not filled from pager handler. no workaround for the moment, just use empty view, it will be filled with actual values when drag is stopped. upd: quick workaround: disable adapter's destroyItem.

you may look at the logcat to understand whats happening in this sample

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

    <TextView xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/calendar_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:padding="5dp"
        android:layout_gravity="center_horizontal"
        android:text="Text Text Text"
    />

</RelativeLayout>

And then:

public class ActivityCalendar extends Activity
{
    public class CalendarAdapter extends PagerAdapter
    {
        @Override
        public int getCount()
        {
            return 3;
        }

        @Override
        public boolean isViewFromObject(View view, Object object)
        {
            return view == ((RelativeLayout) object);
        }

        @Override
        public Object instantiateItem(ViewGroup container, int position)
        {
            LayoutInflater inflater = (LayoutInflater)ActivityCalendar.this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View viewLayout = inflater.inflate(R.layout.layout_calendar, container, false);
            viewLayout.setTag(new Integer(position));

            //TextView tv = (TextView) viewLayout.findViewById(R.id.calendar_text);
            //tv.setText(String.format("Text Text Text relative: %d", position));

            if (!ActivityCalendar.this.scrolledOnce)
            {
                // fill here only first time, the rest will be overriden in pager scroll handler
                switch (position)
                {
                    case 0:
                        ActivityCalendar.this.setPageContent(viewLayout, globalPosition - 1);
                        break;
                    case 1:
                        ActivityCalendar.this.setPageContent(viewLayout, globalPosition);
                        break;
                    case 2:
                        ActivityCalendar.this.setPageContent(viewLayout, globalPosition + 1);
                        break;
                }
            }

            ((ViewPager) container).addView(viewLayout);

            //Log.i("instantiateItem", String.format("position = %d", position));

            return viewLayout;
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object)
        {
            ((ViewPager) container).removeView((RelativeLayout) object);

            //Log.i("destroyItem", String.format("position = %d", position));
        }
    }

    public void setPageContent(View viewLayout, int globalPosition)
    {
        if (viewLayout == null)
            return;
        TextView tv = (TextView) viewLayout.findViewById(R.id.calendar_text);
        tv.setText(String.format("Text Text Text global %d", globalPosition));
    }

    private boolean scrolledOnce = false;
    private int focusedPage = 0;
    private int globalPosition = 0;

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

        final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);

        viewPager.setOnPageChangeListener(new OnPageChangeListener()
        {
            @Override
            public void onPageSelected(int position)
            {
                focusedPage = position;
                // actual page change only when position == 1
                if (position == 1)
                    setTitle(String.format("relative: %d, global: %d", position, globalPosition));
                Log.i("onPageSelected", String.format("focusedPage/position = %d, globalPosition = %d", position, globalPosition));
            }

            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels)
            {
                //Log.i("onPageScrolled", String.format("position = %d, positionOffset = %f", position, positionOffset));
            }

            @Override
            public void onPageScrollStateChanged(int state)
            {
                Log.i("onPageScrollStateChanged", String.format("state = %d, focusedPage = %d", state, focusedPage));
                if (state == ViewPager.SCROLL_STATE_IDLE)
                {
                    if (focusedPage == 0)
                        globalPosition--;
                    else if (focusedPage == 2)
                        globalPosition++;

                    scrolledOnce = true;

                    for (int i = 0; i < viewPager.getChildCount(); i++)
                    {
                        final View v = viewPager.getChildAt(i);
                        if (v == null)
                            continue;

                        // reveal correct child position
                        Integer tag = (Integer)v.getTag();
                        if (tag == null)
                            continue;

                        switch (tag.intValue())
                        {
                            case 0:
                                setPageContent(v, globalPosition - 1);
                                break;
                            case 1:
                                setPageContent(v, globalPosition);
                                break;
                            case 2:
                                setPageContent(v, globalPosition + 1);
                                break;
                        }
                    }

                    Log.i("onPageScrollStateChanged", String.format("globalPosition = %d", globalPosition));

                    viewPager.setCurrentItem(1, false);
                }
            }
        });

        CalendarAdapter calendarAdapter = this.new CalendarAdapter();
        viewPager.setAdapter(calendarAdapter);

        // center item
        viewPager.setCurrentItem(1, false);
    }
}

User · Answer

For infinite scrolling with days it s important you have the good fragment in the pager therefore I wrote my answer on this on page  Viewpager in Android to switch between days endlessly   It s working very well  Above answers did not work for me as I wanted it to work

User · Answer

Actually  I ve been looking at the various ways to do this  infinite  pagination  and even though the human notion of time is that it is infinite  even though we have a notion of the beginning and end of time   computers deal in the discrete  There is a minimum and maximum time  that can be adjusted as time goes on  remember the basis of the Y2K scare      Anyways  the point of this discussion is that it is should be sufficient to support a relatively infinite date range through an actually finite date range  A great example of this is the Android framework s CalendarView implementation  and the WeeksAdapter within it  The default minimum date is in 1900 and the default maximum date is in 2100  this should cover 99  of the calendar use of anyone within a 10 year radius around today easily    What they do in their implementation  focused on weeks  is compute the number of weeks between the minimum and maximum date  This becomes the number of pages in the pager  Remember that the pager doesn t need to maintain all of these pages simultaneously  setOffscreenPageLimit int    it just needs to be able to create the page based on the page number  or index position   In this case the index is the number of weeks that the week is from the minimum date  With this approach you just have to maintain the minimum date and the number of pages  distance to the maximum date   then for any page you can easily compute the week associated with that page  No dancing around the fact that ViewPager doesn t support looping  a k a infinite pagination   and trying to force it to behave like it can scroll infinitely   new FragmentStatePagerAdapter getFragmentManager           Override     public Fragment getItem int index            final Bundle arguments   new Bundle getArguments             final Calendar temp calendar   Calendar getInstance            temp calendar setTimeInMillis  minimum date getTimeInMillis             temp calendar setFirstDayOfWeek  calendar getStartOfWeek             temp calendar add Calendar WEEK OF YEAR  index              Moves to the first day of this week         temp calendar add Calendar DAY OF YEAR                  -UiUtils modulus temp calendar get Calendar DAY OF WEEK  - temp calendar getFirstDayOfWeek                    7            arguments putLong KEY DATE  temp calendar getTimeInMillis             return Fragment instantiate getActivity    WeekDaysFragment class getName    arguments               Override     public int getCount             return  total number of weeks             Then WeekDaysFragment can easily display the week starting at the date passed in its arguments   Alternatively  it seems that some version of the Calendar app on Android uses a ViewSwitcher  which means there s only 2 pages  the one you see and the hidden page   It then changes the transition animation based on which way the user swiped and renders the next previous page accordingly  In this way you get infinite pagination because it just switching between two pages infinitely  This requires using a View for the page though  which is way I went with the first approach   In general  if you want  infinite pagination   it s probably because your pages are based off of dates or times somehow  If this is the case consider using a finite subset of time that is relatively infinite instead  This is how CalendarView is implemented for example  Or you can use the ViewSwitcher approach  The advantage of these two approaches is that neither does anything particularly unusual with the ViewSwitcher or ViewPager  and doesn t require any tricks or reimplementation to coerce them to behave infinitely  ViewSwitcher is already designed to switch between views infinitely  but ViewPager is designed to work on a finite  but not necessarily constant  set of pages

User · Answer

I solved this problem very simply using a little hack in the adapter  Here is my code   public class MyPagerAdapter extends FragmentStatePagerAdapter       public static int LOOPS COUNT   1000      private ArrayList lt Product gt  mProducts        public MyPagerAdapter FragmentManager manager  ArrayList lt Product gt  products                super manager           mProducts   products               Override     public Fragment getItem int position                if  mProducts    null  amp  amp  mProducts size    gt  0                        position   position   mProducts size       use modulo for infinite cycling             return MyFragment newInstance mProducts get position                      else                       return MyFragment newInstance null                          Override     public int getCount                 if  mProducts    null  amp  amp  mProducts size    gt  0                        return mProducts size   LOOPS COUNT     simulate infinite by big number of products                   else                       return 1                       And then  in the ViewPager  we set current page to the middle   mAdapter   new MyPagerAdapter getSupportFragmentManager    mProducts   mViewPager setAdapter mAdapter   mViewPager setCurrentItem mViewPager getChildCount     MyPagerAdapter LOOPS COUNT   2  false      set current item in the adapter to middle

User · Answer

Infinite view pager by overriding 4 adapter methods in your existing adapter class       Override     public int getCount             return Integer MAX VALUE              Override     public CharSequence getPageTitle int position            String title   mTitleList get position   mActualTitleListSize           return title              Override     public Object instantiateItem ViewGroup container  int position            int virtualPosition   position   mActualTitleListSize          return super instantiateItem container  virtualPosition               Override     public void destroyItem ViewGroup container  int position  Object object            int virtualPosition   position   mActualTitleListSize          super destroyItem container  virtualPosition  object

User · Answer

I built a library that can make any ViewPager  pagerAdapter  or FragmentStatePagerAdapter   and optional TabLayout infinitely Scrolling   https   github com memorex386 infinite-scroll-viewpager-w-tabs

User · Answer

Its hacked by CustomPagerAdapter   MainActivity java   import android content Context  import android os Handler  import android os Parcelable  import android support v4 app FragmentPagerAdapter  import android support v4 app FragmentStatePagerAdapter  import android support v4 view PagerAdapter  import android support v4 view ViewPager  import android support v7 app AppCompatActivity  import android os Bundle  import android util Log  import android view LayoutInflater  import android view View  import android view ViewGroup  import android widget LinearLayout  import android widget TextView  import java util ArrayList  import java util List   public class MainActivity extends AppCompatActivity        private List lt String gt  numberList   new ArrayList lt String gt         private CustomPagerAdapter mCustomPagerAdapter      private ViewPager mViewPager      private Handler handler      private Runnable runnable        Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           setContentView R layout activity main            numberList clear            for  int i   0  i  lt  10  i              numberList add    i                      mViewPager    ViewPager findViewById R id pager           mCustomPagerAdapter   new CustomPagerAdapter MainActivity this           EndlessPagerAdapter mAdapater   new EndlessPagerAdapter mCustomPagerAdapter           mViewPager setAdapter mAdapater             mViewPager addOnPageChangeListener new ViewPager OnPageChangeListener                  Override             public void onPageScrolled int position  float positionOffset  int positionOffsetPixels                                 Override             public void onPageSelected int position                    int modulo   position numberList size                    Log i  Current ViewPager View s Position      modulo                                Override             public void onPageScrollStateChanged int state                                        handler   new Handler            runnable   new Runnable                  Override             public void run                      mViewPager setCurrentItem mViewPager getCurrentItem   1                   handler postDelayed runnable  1000                                     handler post runnable                Override     protected void onDestroy             if handler  null               handler removeCallbacks runnable                     super onDestroy               private class CustomPagerAdapter extends PagerAdapter            Context mContext          LayoutInflater mLayoutInflater           public CustomPagerAdapter Context context                mContext   context              mLayoutInflater    LayoutInflater  mContext getSystemService Context LAYOUT INFLATER SERVICE                       Override         public int getCount                 return numberList size                        Override         public boolean isViewFromObject View view  Object object                return view      LinearLayout  object                       Override         public Object instantiateItem ViewGroup container  int position                View itemView   mLayoutInflater inflate R layout row item viewpager  container  false                TextView textView    TextView  itemView findViewById R id txtItem               textView setText numberList get position                container addView itemView               return itemView                      Override         public void destroyItem ViewGroup container  int position  Object object                container removeView  LinearLayout  object                        private class EndlessPagerAdapter extends PagerAdapter            private static final String TAG    EndlessPagerAdapter           private static final boolean DEBUG   false           private final PagerAdapter mPagerAdapter           EndlessPagerAdapter PagerAdapter pagerAdapter                if  pagerAdapter    null                    throw new IllegalArgumentException  Did you forget initialize PagerAdapter                               if   pagerAdapter instanceof FragmentPagerAdapter    pagerAdapter instanceof FragmentStatePagerAdapter   amp  amp  pagerAdapter getCount    lt  3                    throw new IllegalArgumentException  When you use FragmentPagerAdapter or FragmentStatePagerAdapter  it only supports  gt   3 pages                               mPagerAdapter   pagerAdapter                      Override         public void destroyItem ViewGroup container  int position  Object object                if  DEBUG  Log d TAG   Destroy      getVirtualPosition position                mPagerAdapter destroyItem container  getVirtualPosition position   object                if  mPagerAdapter getCount    lt  4                    mPagerAdapter instantiateItem container  getVirtualPosition position                                      Override         public void finishUpdate ViewGroup container                mPagerAdapter finishUpdate container                       Override         public int getCount                 return Integer MAX VALUE     this is the magic that we can scroll infinitely                      Override         public CharSequence getPageTitle int position                return mPagerAdapter getPageTitle getVirtualPosition position                        Override         public float getPageWidth int position                return mPagerAdapter getPageWidth getVirtualPosition position                        Override         public boolean isViewFromObject View view  Object o                return mPagerAdapter isViewFromObject view  o                       Override         public Object instantiateItem ViewGroup container  int position                if  DEBUG  Log d TAG   Instantiate      getVirtualPosition position                return mPagerAdapter instantiateItem container  getVirtualPosition position                        Override         public Parcelable saveState                 return mPagerAdapter saveState                        Override         public void restoreState Parcelable state  ClassLoader loader                mPagerAdapter restoreState state  loader                       Override         public void startUpdate ViewGroup container                mPagerAdapter startUpdate container                      int getVirtualPosition int realPosition                return realPosition   mPagerAdapter getCount                       PagerAdapter getPagerAdapter                 return mPagerAdapter                       activity main xml    lt  xml version  1 0  encoding  utf-8   gt   lt RelativeLayout xmlns android  http   schemas android com apk res android      xmlns tools  http   schemas android com tools  android layout width  match parent      android layout height  match parent  android paddingLeft   dimen activity horizontal margin      android paddingRight   dimen activity horizontal margin      android paddingTop   dimen activity vertical margin      android paddingBottom   dimen activity vertical margin  tools context   MainActivity  gt        lt android support v4 view ViewPager xmlns android  http   schemas android com apk res android          android id    id pager          android layout width  match parent          android layout height  180dp  gt       lt  android support v4 view ViewPager gt    lt  RelativeLayout gt    row item viewpager xml    lt  xml version  1 0  encoding  utf-8   gt   lt LinearLayout xmlns android  http   schemas android com apk res android      android layout width  match parent  android layout height  match parent      android gravity  center  gt        lt TextView         android layout width  wrap content          android layout height  wrap content          android id    id txtItem          android textAppearance   android style TextAppearance Large   gt    lt  LinearLayout gt    Done

User · Answer

All you need to do is look at the example here You will find that in line 295 the page is always set to 1 so that it is scrollable and that the count of pages is 3 in getCount   method  Those are the 2 main things you need to change  the rest is your logic and you can handle them differently  Just make a personal counter that counts the real page you are on because position will no longer be usable after always setting current page to 1 on line 295  p s  this code is not mine it was referenced in the question you linked in your question

User · Answer

Based on https   github com antonyt InfiniteViewPager I wrote up this which works nicely   class InfiniteViewPager  JvmOverloads constructor    context  Context    attrs  AttributeSet    null     ViewPager context  attrs         Allow for 100 back cycles from the beginning       This should be enough to create an illusion of infinity       Warning  scrolling to very high values  1 000 000   results in strange drawing behaviour    private val offsetAmount get     if  adapter  count    0  0 else  adapter as InfinitePagerAdapter  realCount   100    override fun setAdapter adapter  PagerAdapter         super setAdapter if  adapter    null  null else InfinitePagerAdapter adapter       currentItem   0        override fun setCurrentItem item  Int    setCurrentItem item  false     override fun setCurrentItem item  Int  smoothScroll  Boolean        val adapterCount   adapter  count      if  adapterCount    null    adapterCount    0          super setCurrentItem item  smoothScroll        else         super setCurrentItem offsetAmount   item   adapterCount  smoothScroll               override fun getCurrentItem    Int       val adapterCount   adapter  count      return if  adapterCount    null    adapterCount    0          super getCurrentItem         else         val position   super getCurrentItem         position    adapter as InfinitePagerAdapter  realCount              fun animateForward         super setCurrentItem super getCurrentItem     1  true         fun animateBackwards         super setCurrentItem super getCurrentItem   - 1  true         internal class InfinitePagerAdapter private val adapter  PagerAdapter    PagerAdapter         internal val realCount  Int get     adapter count      override fun getCount     if  realCount    0  0 else Integer MAX VALUE      override fun instantiateItem container  ViewGroup  position  Int    adapter instantiateItem container  position   realCount       override fun destroyItem container  ViewGroup  position  Int   object   Any    adapter destroyItem container  position   realCount   object        override fun finishUpdate container  ViewGroup    adapter finishUpdate container       override fun isViewFromObject view  View   object   Any    adapter isViewFromObject view   object        override fun restoreState bundle  Parcelable   classLoader  ClassLoader     adapter restoreState bundle  classLoader       override fun saveState    Parcelable    adapter saveState        override fun startUpdate container  ViewGroup    adapter startUpdate container       override fun getPageTitle position  Int    adapter getPageTitle position   realCount       override fun getPageWidth position  Int    adapter getPageWidth position       override fun setPrimaryItem container  ViewGroup  position  Int   object   Any    adapter setPrimaryItem container  position   object        override fun unregisterDataSetObserver observer  DataSetObserver    adapter unregisterDataSetObserver observer       override fun registerDataSetObserver observer  DataSetObserver    adapter registerDataSetObserver observer       override fun notifyDataSetChanged     adapter notifyDataSetChanged        override fun getItemPosition  object   Any    adapter getItemPosition  object           For consuming it simply change your ViewPager to InfiniteViewPager and that s all you need to change

User · Answer

Thank you for your answer Shereef   I solved it a little bit differently   I changed the code of the ViewPager class of the android support library  The method setCurrentItem int   changes the page with animation  This method calls an internal method that requires the index and a flag enabling smooth scrolling  This flag is boolean smoothScroll  Extending this method with a second parameter boolean smoothScroll solved it for me  Calling this method setCurrentItem int index  boolean smoothScroll  allowed me to make it scroll indefinitely   Here is a full example   Please consider that only the center page is shown  Moreover did I store the pages seperately  allowing me to handle them with more ease   private class Page     View page    List lt    gt  data       page for predecessor  current  and successor Page   pages   new Page 3       mDayPager setOnPageChangeListener new ViewPager OnPageChangeListener               Override         public void onPageSelected int position                        Override         public void onPageScrolled int position  float positionOffset  int positionOffsetPixels               Override         public void onPageScrollStateChanged int state                 if  state    ViewPager SCROLL STATE IDLE                     if  mFocusedPage    0                           move some stuff from the                                                 center to the right here                     moveStuff pages 1   pages 2                            move stuff from the left to the center                      moveStuff pages 0   pages 1                           retrieve new stuff and insert it to the left page                     insertStuff pages 0                                      else if  mFocusedPage    2                             move stuff from the center to the left page                     moveStuff pages 1   pages 0                            move stuff from the right to the center page                     moveStuff pages 2   pages 1                            retrieve stuff and insert it to the right page                                             insertStuff pages 2                                          go back to the center allowing to scroll indefinitely                 mDayPager setCurrentItem 1  false                                     However  without Jon Willis Code I wouldn t have solved it myself    EDIT  here is a blogpost about this

[android] Changing ViewPager to enable infinite page scrolling

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