Patterns when to use Activity Transition vs Dynamic Fragments

Question

Are there any patterns on how to handle UI Transitions in Android Activities vs Fragments? I am currently looking into a UI that has at most 3 columns in Landscape. I would like the UI to start with 1 column all the way across the screen and then on selection of something move in the second column and then on clicking on something in the second fade in the 3rd on tablets and phones and fade out the 1st column on phones. I am wondering when I should do this as an Activity transition and when I should just use Fragments with Views that Appear. As far as I have read fragments can be moved over to other activities so my choice is either implement Activities with static column layouts that then transition taking the fragments with them or have one Activity with all 3 columns and have the Activity manage the Appearing of the Fragments. Both approaches could work but I was interested in pros and cons from as many angles for both solutions.

There are two questions similar to what I am asking but don't quite answer mine

• Two panel UI with Fragments vs Separate activities
• Android Honeycomb: layout problem - hide/show FrameLayouts

Answer 1

Fragments can seem like more code up front (since you're putting a view in a fragment, and a fragment in an Activity, instead of just a view in an Activity), but they're great at saving you from headaches in just this kind of situation- Definitely go with Fragments. They even handle the transitions for you.

We have some sample code called "Honeycomb Gallery" you can take a look at here, which has a two-column-plus-actionbar layout, and the ability to show/hide the leftmost column. This should give you a good head start in figuring out how to do layout for multiple fragments and show/hide them.

FYI, one important trade-off to using multiple fragments in an Activity instead of multiple Activities, is that fragments don't directly respond to intents - For instance, if you had a note-taking app where "View Note" page was an Activity, and you changed it so that there was a "view note" Fragment inside the main Activity, then you'd have to set it up such that the main Activity received a note ID AND a note action (create, view, edit, whatever) in the Intent, as opposed to just having the "view note" activity receive the note ID in the Intent. The main Activity would then need to set up the fragments on the page accordingly. Not a huge deal, but if external accessibility to various parts of your application via Intent is important, then it might be easier to break your app out into a few Activities, as well as use fragments to represent the individual components.

Answer 2

Based on the page The Android 3.0 Fragments API, an Activity is stand alone while a fragment can be though of as as a mini-Activity, which must be hosted within an actual Activity.

It goes on to say that the introduction of the Fragment API gave the android developers the opportunity to address many of the pain points developers hit with Activities, so in Android 3.0 the utility of Fragment extends far beyond just adjusting for different screens:

I think that using a single activity for an app is not necessarily a wrong decision, just a matter of style. It is a decision that you should make based on what you are trying to accomplish.

However, the introduction of Fragments was seen to solve real world problems. Based on that alone, I would recommend that you writing some "Proof of Concept" code and evaluate the results. At this time, this may be the only real world test that will matter

Answer 3

Use Activities for Full Screen

Use Fragments for Part of or no Screen (but not a service)

In my main application, there is on-screen tabs in a horizontal scroll-view I wanted to persist across multiple sections of the app. Sections include News,Photos,Videos,Schedule etc. All single-user focusable tasks.

The main Application that houses it all is a application, and the tabs are just a view which call the fragment Manager.

However, I use Activities for complicated user activities deeper in the application. E.g. if someone plays a video, views a item detail page and the photo-gallery/slideshow sections, because they are all full screen components.

There is no need to show/hide fragments when transitioning to full screen because the activity stack handles everything you want to do it quickly and easily, and keep your code minimal and clean.

So I have Activity -> houses fragments -> launch full screen Activities for special commands.