Use View or Fragment in ViewPager

Question

I have a question about whether to use View or Fragment with ViewPager.

Background: I have an Activity A that contains a ListView. Each ListView item opens Activity B. Activity B shows different content depending on which ListView item is tapped in Activity A. Activity B's content is shown inside a ListView.

Question: Now, instead of going back and forth between Activity A and B to switch contents, I have a requirement to implement horizontal view swiping to switch contents all within Activity B. One solution I found (tried it and it works) is to create many instances of Activity B's ListView and use it with ViewPager + PagerAdapter. Another potential solution found on the doc (haven't tried it) is to bring that ListView into a Fragment, create many instances of the fragment and use it with ViewPager + FragmentPagerAdapter or FragmentStatePagerAdapter.

My question is, what's the benefit of using each approach? Should I go through all the trouble of bringing the ListView into Fragment or just simply use ListView with ViewPager?

Thanks

Answer 1

A Fragment is a useful approach, I think, when you want to tie some UI business logic to a particular View (or group of). As you know, that individual Fragment has its own lifecycle callbacks and so forth, just as an Activity would.

Rather than having a single Activity host many ListViews through a single PagerAdapter, it may be cleaner to use the Fragment approach because the Fragment only needs to deal with the logic behind driving a single ListView.

This is a very similar situation to one I've just been facing. I'm showing various vertically scrolling forms (consisting of lots of input fields) within a ViewPager. In my case I have gone for the Fragment approach because in my case, it's possible that the ViewPager will actually need to display a completely different kind of view on certain pages. For example, on the first few pages, user input forms might be displayed. But on the final page, a graph will be displayed. A whole separate set of logic is required to drive that graph. To drive those input forms and one graph from a single Activity would get a bit messy, and I would probably need to contain the business logic in several delegate classes or something. So for me, Fragments were the obvious choice in the end. I have my InputFormFragment and a GraphFragment, and they each contain only the applicable logic for the Views that they supply.

Another thing to consider is that in the near future you too may want to display a different kind of View in your ViewPager. Or, you might want to have another UI layout altogether, perhaps one that doesn't use the ViewPager but displays them all side-to-side (e.g. a layout used on a large tablet in landscape mode). With Fragments, things are just far more modular and you could factor the code to do this quicker. If on the other hand you achieved your objective by using a single Activity that contains a simple PagerAdapter and all the logic for the ListViews within, you might find it takes more work in the future to support new kinds of Views or special tablet layouts.

One thing I will say is having implemented Fragments in a ViewPager myself through FragmentPagerAdapter and FragmentStatePagerAdapter, things can get a bit awkward if you have any special requirements; managing Fragments can be tricky sometimes. For example, for my UI I needed to be able to programmatically add and remove the ViewPager containing the Fragments. I also needed to ensure that the adapter in use didn't destroy Fragments once they had been shown, because I needed to collect data from all Fragments simultaneously at a certain point. Furthermore, I had to extend and modify FragmentPagerAdatper to make sure that the Fragments go through their onDestroy() properly and are removed from the FragmentManager when the ViewPager was removed.

Fragments enable a very modular way of constructing UIs for various screen sizes and orientations, and are excellent in how they allow you to encapsulate business logic and lifecycles for individual UI elements. However if your scenario really is just as simple as several ListViews in a ViewPager and you know that you will never need the modularity, then the overhead of Fragments could be an overkill.