Question

I find Fragment#setRetainInstance(true) confusing. Here is the Javadoc, extracted from the Android Developer API:

public void setRetainInstance (boolean retain)

Control whether a fragment instance is retained across Activity re-creation (such as from a configuration change). This can only be used with fragments not in the back stack. If set, the fragment lifecycle will be slightly different when an activity is recreated:

• onDestroy() will not be called (but onDetach() still will be, because the fragment is being detached from its current activity).
• onCreate(Bundle) will not be called since the fragment is not being re-created.
• onAttach(Activity) and onActivityCreated(Bundle) will still be called.

Question: How do you as a developer use this, and why does it make things easier?

Answer 1

How do you as a developer use this

Call setRetainInstance(true). I typically do that in onCreateView() or onActivityCreated(), where I use it.

and why does it make things easier?

It tends to be simpler than onRetainNonConfigurationInstance() for handling the retention of data across configuration changes (e.g., rotating the device from portrait to landscape). Non-retained fragments are destroyed and recreated on the configuration change; retained fragments are not. Hence, any data held by those retained fragments is available to the post-configuration-change activity.