Getting data (asynchronous) and populating ViewPager's fragments

Question

I have an activity with a ViewPager with a variable number of fragments (tabs).

Upon start the activity checks if the associated (complex) data has been loaded. If it hasn't it shows a progress bar view and starts an AsyncTask which fetches the data. Depending on the data the activity creates a number of fragments (tabs) and gives each fragment a sub set of the data.

I currently hold references to the fragments (I know that it is discouraged) and I run into all sorts of problems when the fragments gets reused - I'm giving the data to the wrong instance of the fragment.

So, is there an "android way" of solving this problem?

Answer 1

I run into all sorts of problems when the fragments gets reused

Fragments usually don't get reused in a ViewPager. This is not like an AdapterView where rows get recycled. Using FragmentPagerAdapter or FragmentStatePagerAdapter, a fragment represents one and only one page.

I re-instantiate the ViewPager each time (but the fragments get reused?)

Ah. That's a slightly different problem.

The stock implementations of FragmentPagerAdapter and FragmentStatePagerAdapter make a couple of assumptions:

1. They are in complete control over the fragments, particularly in terms of running the transactions to add and remove them from the UI

2. That those fragments will only ever be used by one "logical" ViewPager (IOW, recreating that ViewPager for a configuration change is fine, but that' pretty much it)

Complicating matters is that these adapters store the fragments under certain tags, and therefore if those fragments still exist in those tags, those existing ones will get used, instead of new ones being created.

So, is there an "android way" of solving this problem?

It's unclear from your question why you even need to "re-instantiate the ViewPager". I'm assuming that this is tied to some sort of refresh operation, or something else that is forcing you to go through the process described in your second paragraph.

You could give my ArrayPagerAdpater a try, as it is friendlier about external agents mucking about with the fragments. Since you control the fragments' tags, you can always be certain that you are working with the right fragment -- rather than caching them yourself, just retrieve the right one and manipulate it.