FragmentStatePagerAdapter performance issue

Question

I have implemented an activity that displays fragments in a viewpager. The activity initially displays 5 fragments of a given type (type A). Each type A fragment contains a list of information. When a button is pressed, the fragments are replaced with another tpye of fragments, type B (i.e., fragments that use a different layout and display different information are loaded).

I have implemented this with a ViewPager and a custom FragmentStatePagerAdapter. The custom FragmentStatePagerAdapter overrides the getCount, instantiateItem, getItem, getItemPosition, etc. functions and all works fine. When I press the button the views switch from fragment type A to fragment type B. In order to do this I am using a replace fragment transaction and I also call notifyDataSetChanged on the adapter. The switch from type A to type B fragments is accomplished by checking which type of fragment I need to create in the adapter's getItem function. The problem is that the switching process (i.e., changing from fragment type A to fragment type B and vice versa) takes some time (around 2 seconds) - this delay is quite noticeable and annoying.

This occurs because the adapter's getItemPosition function returns POSITION_NONE. When POSITION_NONE is returned, the viewPager recreates the fragment. Furthermore, when the replace transaction is executed, all items of the adapter are removed and all new ones are recreated. The same happens when I switch back to fragments type A.

Does anyone know if there is a better or faster way to do this? Using a FragmentPagerAdapter should not be a good solution since the number of fragments in the viewPager could grow.

I have commented out the updating of the fragments and the problem is gone so the problem is the time it takes to update the fragments. Is there a way to update the fragments asynchronously? That should take care of the problem.

Answer 1

The ViewPager instatiates by default a minimun count of Fragments. In general the left and right one of the current Fragment. So you don't need to care about the total number of Fragments.

You can control the total number with the ViewPager.setOffScreenPageLimit() method.

Also a AsyncTask seems to be a good idea to manage the intensiv work of your Fragments.