What is the difference between FragmentPagerAdapter and FragmentStatePagerAdapter

Question

What is the difference between FragmentPagerAdapter and FragmentStatePagerAdapter   About FragmentPagerAdapter Google s guide says      This version of the pager is best for use when there are a handful of   typically more static fragments to be paged through  such as a set of   tabs  The fragment of each page the user visits will be kept in   memory  though its view hierarchy may be destroyed when not visible    This can result in using a significant amount of memory since fragment   instances can hold on to an arbitrary amount of state  For larger sets   of pages  consider FragmentStatePagerAdapter    And about FragmentStatePagerAdapter      This version of the pager is more useful when there are a large number   of pages  working more like a list view  When pages are not visible to   the user  their entire fragment may be destroyed  only keeping the   saved state of that fragment  This allows the pager to hold on to much   less memory associated with each visited page as compared to   FragmentPagerAdapter at the cost of potentially more overhead when   switching between pages    So I have just 3 fragments  But all of them are separate modules with a large amount of data   Fragment1 handles some data  which users enter  and passes it via activity into Fragment2  which is just a simple ListFragment  Fragment3 is also a ListFragment   So my questions are  Which adapter should I use  FragmentPagerAdapter or FragmentStatePagerAdapter

User · Answer

FragmentStatePagerAdapter   with FragmentStatePagerAdapter your unneeded fragment is destroyed A transaction is committed to completely remove the fragment from your activity s FragmentManager   The state in FragmentStatePagerAdapter comes from the fact that it will save out your fragment s Bundle from savedInstanceState when it is destroyed When the user navigates back the new fragment will be restored using the fragment s state    FragmentPagerAdapter   By comparision FragmentPagerAdapter does nothing of the kind When the fragment is no longer needed FragmentPagerAdapter calls detach Fragment  on the transaction instead of remove Fragment    This destroy s the fragment s view but leaves the fragment s instance alive in the FragmentManager so the fragments created in the FragmentPagerAdapter are never destroyed

User · Answer

FragmentPagerAdapter stores the previous data which is fetched from the adapter while FragmentStatePagerAdapter takes the new value from the adapter everytime it is executed

User · Answer

Here is a log lifecycle of each fragment in ViewPager which have 4 fragment and offscreenPageLimit   1  default value   FragmentStatePagerAdapter  Go to Fragment1  launch activity   Fragment1  onCreateView Fragment1  onStart Fragment2  onCreateView Fragment2  onStart   Go to Fragment2  Fragment3  onCreateView Fragment3  onStart   Go to Fragment3  Fragment1  onStop Fragment1  onDestroyView Fragment1  onDestroy Fragment1  onDetach Fragment4  onCreateView Fragment4  onStart   Go to Fragment4  Fragment2  onStop Fragment2  onDestroyView Fragment2  onDestroy   FragmentPagerAdapter  Go to Fragment1  launch activity   Fragment1  onCreateView Fragment1  onStart Fragment2  onCreateView Fragment2  onStart   Go to Fragment2  Fragment3  onCreateView Fragment3  onStart   Go to Fragment3  Fragment1  onStop Fragment1  onDestroyView Fragment4  onCreateView Fragment4  onStart   Go to Fragment4  Fragment2  onStop Fragment2  onDestroyView   Conclusion  FragmentStatePagerAdapter call onDestroy when the Fragment is overcome offscreenPageLimit while FragmentPagerAdapter not     Note  I think we should use FragmentStatePagerAdapter for a ViewPager which have a lot of page because it will good for performance   Example of offscreenPageLimit    If we go to Fragment3  it will detroy Fragment1  or Fragment5 if have  because offscreenPageLimit   1  If we set offscreenPageLimit  gt  1 it will not destroy  If in this example  we set offscreenPageLimit 4  there is no different between using FragmentStatePagerAdapter or FragmentPagerAdapter because Fragment never call onDestroyView and onDestroy when we change tab   Github demo here

User · Answer

Something that is not explicitly said in the documentation or in the answers on this page  even though implied by  Naruto   is that FragmentPagerAdapter will not update the Fragments if the data in the Fragment changes because it keeps the Fragment in memory   So even if you have a limited number of Fragments to display  if you want to be able to refresh your fragments  say for example you re-run the query to update the listView in the Fragment   you need to use FragmentStatePagerAdapter   My whole point here is that the number of Fragments and whether or not they are similar is not always the key aspect to consider  Whether or not your fragments are dynamic is also key

User · Answer

FragmentPagerAdapter  the fragment of each page the user visits will be stored in memory  although the view will be destroyed  So when the page is visible again  the view will be recreated but the fragment instance is not recreated  This can result in a significant amount of memory being used  FragmentPagerAdapter should be used when we need to store the whole fragment in memory  FragmentPagerAdapter calls detach Fragment  on the transaction instead of remove Fragment    FragmentStatePagerAdapter  the fragment instance is destroyed when it is not visible to the User  except the saved state of the fragment  This results in using only a small amount of Memory and can be useful for handling larger data sets  Should be used when we have to use dynamic fragments  like fragments with widgets  as their data could be stored in the savedInstanceState Also it won   t affect the performance even if there are large number of fragments

User · Answer

Like the docs say  think about it this way  If you were to do an application like a book reader  you will not want to load all the fragments into memory at once  You would like to load and destroy Fragments as the user reads  In this case you will use FragmentStatePagerAdapter  If you are just displaying 3  tabs  that do not contain a lot of heavy data  like Bitmaps   then FragmentPagerAdapter might suit you well  Also  keep in mind that ViewPager by default will load 3 fragments into memory  The first Adapter you mention might destroy View hierarchy and re load it when needed  the second Adapter only saves the state of the Fragment and completely destroys it  if the user then comes back to that page  the state is retrieved

User · Answer

FragmentStatePagerAdapter   To accommodate a large number of fragments in ViewPager  As this adapter destroys the fragment when it is not visible to the user and only savedInstanceState of the fragment is kept for further use  This way a low amount of memory is used and a better performance is delivered in case of dynamic fragments

[android] What is the difference between FragmentPagerAdapter and FragmentStatePagerAdapter?

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