Sources of Owners

observe() on a LiveData takes a LifecycleOwner. Technically, you could implement the LifecycleOwner interface on just about anything. In practice, there are three commonly-used LifecycleOwner implementations:

1. FragmentActivity and things that inherit from it, like AppCompatActivity
2. Fragment
3. The “view LifecycleOwner” of a Fragment

The first two are fairly straightforward. They let the LiveData know about the lifecycle of the activity and the fragment, respectively.

However, as we noted earlier fragments are weird, with their pair of lifecycles:

1. The lifecycle of the fragment itself
2. The lifecycle of a particular UI managed by that fragment

The general rule of thumb is:

• If you are observing a LiveData solely for populating a UI, such as we are doing here in ColorListFragment, use getViewLifecycleOwner() as the LifecycleOwner and start observing in onViewCreated() (or possibly in onCreateView())
• If you are observing a LiveData and need to observe for the entire lifetime of the fragment, regardless of its UI, use the Fragment itself as the LifecycleOwner and start observing in onCreate()… but do not attempt to update any views in response to that LiveData, as they may not exist at the time you receive an updated value

The first pattern is by far the most common one.