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Keeping ListFragments in a FragmentPager in sync

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By User



Let's say I have a list of homogenous items which is likely to be changed in the lifetime of my Activity by user interaction or OS events. The Activity contains a FragmentPager which shows a number of ListFragment s.





These fragments share the previously mentioned data but display it in different ways. E.g. they differ in sorting order or display only a subset of the data. Currently each fragment keeps a separate list containing the respective part of the data in the respective order.





When the data changes, basicly every fragment has to be updated. This means resorting or adding/removing items from some of the fragments. What is the best practice to keep the data in the different fragments consistent?





Currently I have some sort of an observer object, which is notified when something changes and subsequently notifies the connected fragments. But there are a couple of problems:





  • When the app just started, some of the fragments haven't been created by the FragmentPager, so notifying them is impossible.



  • When swiping through the fragments some of them get paused. In this state, they can't update their list. Should they disconnect from the observer in this case? This leads to:



  • When a change happens, while a fragment is disconnected, it basicly misses it.



  • And so on...




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Comments

  1. Tips For AllFebruary 27, 2012 at 7:20 AM

    If I understood your ViewPager shows the same data (or it's portion) but in different views. So, I belive ViewPager shouldn't act in any way when data is changed, it's responsibility of Adapter.

    About points below you said:
    a) creating of fragments inside ViewPager can be managed by you. Just see javadoc of ViewPager::setOffscreenPageLimit(int limit) method.
    b) I think you should do nothing with UI when data changed but fragment is in paused state. If you want to update do it in onResume(). Or better to set some field in DB (if you have) to "updates present" state and check it when Activity(Fragment) appears.
    c) As in previous option - if fragment disconnected just ignore updates. Or if you really interested in that update use sticky BroadcastReciver (be carefull sticky BR is expensive thing)

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