Search code examples
androidandroid-viewpagerfragmentandroid-viewpager2

When to do fragment preparation work in ViewPage2

I am trying to migrate my app from the legacy ViewPager to ViewPage2. And I found that unlike ViewPager, ViewPager2 will not call fragment's onCreate() or onCreateView when the fragment is not visible.

For example, user is on Fragment[N], when using ViewPager, Fragment[N+1] will be created in background and I can do some preparation work there (e.g. start fetching data, decoding image etc.).

However, when I tried the ViewPager2 sample, I found that those fragment lifecycle callbacks only get called when Fragment[N+1] becomes visible to user. Otherwise, only the fragment's constructor(init method) is called in the background. But I need the initialized view objects for the preparation work. So, how to solve this problem? Or if I am doing things in a wrong way, please point out the correct direction.

Thanks a lot.

Solution

  • You can possibly solve some of your problems by adjusting the OffscreenPageLimit

    https://developer.android.com/reference/androidx/viewpager2/widget/ViewPager2#setOffscreenPageLimit(int)

    This will change it to bring the Fragments +/- X number to Started state either side of the current one.

    Only the current displayed Fragment is brought to Resumed State.

    As Viewpager2 is just a recyclerview of Fragments it is optimised to try and be efficient and not create Fragments until they are really needed to be displayed.