androidandroid-fragmentsonsaveinstancestate

Should we use savedInstanceState in fragments if there are getArguments()?

In Android fragments we can get initial data in onCreate() from savedInstanceState or getArguments(). I often check them both for null and then assign variables. For instance, in Kotlin:

val bundle = savedInstanceState ?: arguments
bundle?.let {
    startDate = Date(it.getLong(ARG_START_DATE, 0))
    endDate = Date(it.getLong(ARG_END_DATE, startDate.time))
}

So, first I check whether savedInstanceState != null and if so, will get data from there. If it is null, I will check getArguments() != null and if so will get data from there. Otherwise variables will be null, 0 or false.

When we leave a fragment and call onSaveInstanceState() we can write data to a bundle and later can read them in onCreate(). But we can also write data to getArguments() and read them from any place of the fragment. Why should we use savedInstanceState as we can write to getArguments()?

Solution

  • The main difference between these two options is their storage location.The arguments are stored in memory but The saveInstanceState is serialized to disk. You should look at this page: https://developer.android.com/topic/libraries/architecture/saving-states