Which one to use NavUtils.navigateUpFromSameTask() vs. onBackPressed()

Question

I have two activities A and B. The A has a ListFragment which uses LoaderManager, whereas B activity shows a details about the item selected in the A\'s ListFragment. I\'ve

Answer 1

check out this presentation: https://speakerdeck.com/jgilfelt/this-way-up-implementing-effective-navigation-on-android. It answers to all of your problems.

Answer 2

Solution c is the correct option. First, though, an explanation of the problem with solution a.

There is absolutely no point in having two back buttons in your Activity. Furthermore, option a actually breaks the up button. The point of the up button is to provide a way for users to stay within your app when they have landed in your app from an outside source. For example, if you land on activity B from an outside activity C and if you are using your option a, then pressing "up" in activity B will result in activity C being shown. The behavior you would want would be for activity A to be shown.

As you can see, solution b is on the right track. You definitely want to go up to A and not back to C. However, simply storing the state in onSaveInstanceState will not cause the state to be retained. This is because onSaveInstanceState only gets called if your application may be killed by the system. It is not guaranteed to be called if your application was destroyed manually, and it certainly won't be called when a new instance of your Activity is created. If the Intent starts a new activity, then it will not have its state restored from the other activity.

There solution, then, is that you must write anything persistent to a shared preference file (or a custom persistent alternative). When doing this you can guarantee that all instances of an Activity share the same state across multiple tasks so long as their onResume (or wherever you restore state) is called. OR:

If you know exactly how you want your navigation to work, you can avoid writing everything to persistent state by using a combination of Intent flags and Activity task affinities. If you want to use the same activity as up even if you navigate into the application from an outside source, then you can leave your Activity A's affinity as default (linked to the application) and use something like Intent.FLAG_ACTIVITY_CLEAR_TOP.

Personally, I'd try the Intent flag approach first and failing that fall back to writing the state persistently. You just don't really want scroll location sitting on persistent storage if you can avoid it..