How to change ViewPager s page

Question

I m using ViewPager in my app and define it in the main Activity  Inside onCreate method I load some number of pages from SharedPreferences and then pass it to PagerAdapter    Override public int getCount         return numberOfPages      The problem is that if I would change this number in Preferences  or another Activity  to some other less then page index I viewed before  my app crashes because this index is out of bounds when I return to the activity with this ViewPager  It can be fixed simply by changing active ViewPager s page  Is there any way to do it

User · Accepted Answer

I m not sure that I fully understand the question  but from the title of your question  I m guessing that what you re looking for is pager setCurrentItem  num    That allows you to programatically switch to another page within the ViewPager   I d need to see a stack trace from logcat to be more specific if this is not the problem

User · Answer

Without checking your code  I think what you are describing is that your pages are out of sync and you have stale data   You say you are changing the number of pages  then crashing because you are accessing the old set of pages  This sounds to me like you are not calling pageAdapter notifyDataSetChanged   after changing your data   When your viewPager is showing page 3 of a set of 10 pages  and you change to a set with only 5  then call notifyDataSetChanged    what you ll find is you are now viewing  page 3 of the new set  If you were previously viewing page 8 of the old set  after putting in the new set and calling notifyDataSetChanged   you will find you are now viewing the last page of the new set without crashing   If you simply change your current page  you may just be masking the problem

User · Answer

Supplemental answer  I was originally having trouble getting a reference to the ViewPager from other class methods because the addOnTabSelectedListener made an anonymous inner class  which in turn required the ViewPager variable to be declared final  The solution was to use a class member variable and not use the anonymous inner class   public class MainActivity extends AppCompatActivity        TabLayout tabLayout      ViewPager viewPager        Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           setContentView R layout activity main            Toolbar toolbar    Toolbar  findViewById R id toolbar           setSupportActionBar toolbar            tabLayout    TabLayout  findViewById R id tab layout           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            viewPager    ViewPager  findViewById R id pager           final PagerAdapter adapter   new PagerAdapter getSupportFragmentManager    tabLayout getTabCount             viewPager setAdapter adapter           viewPager addOnPageChangeListener new TabLayout TabLayoutOnPageChangeListener tabLayout                don t use an anonymous inner class here         tabLayout addOnTabSelectedListener tabListener               TabLayout OnTabSelectedListener tabListener   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                              The view pager can now be accessed here  too      public void someMethod             viewPager setCurrentItem 0

User · Answer

for switch to another page  try with this code   viewPager postDelayed new Runnable          Override     public void run                 viewPager setCurrentItem num  true            100

User · Answer

slide to right   viewPager arrowScroll View FOCUS RIGHT    slide to left  viewPager arrowScroll View FOCUS LEFT

[android] How to change ViewPager's page?

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