Why are fragment callbacks different from activity callbacks?

The lifecycle of a fragment is more complex and closely tied to the lifecycle of the activity it is embedded in. A fragment can exist independently of an activity, be added to it, removed, replaced, or placed on the back stack. This requires additional callbacks to manage these states.

Main differences:

• Binding to activity: The fragment has callbacks related to its attachment (onAttach) and detachment (onDetach) from the activity. This allows the fragment to interact with the activity's context.
• Creating View: The fragment has a separate callback onCreateView for creating its view hierarchy, whereas the activity uses setContentView. This is because a fragment can be UI-less.
• Destroying View: The fragment has onDestroyView, which is called when the fragment's view is destroyed, but the fragment itself can still exist (e.g., in the back stack). The activity does not have a direct equivalent.
• Interaction with activity lifecycle: The fragment's lifecycle follows the activity's lifecycle but has its own phases within each activity phase. For example, the fragment's onStart() is called after the activity's onStart().

Key fragment callbacks not present in the activity:

• onAttach()
• onCreateView()
• onViewCreated()
• onDestroyView()
• onDetach()

This allows for more flexible management of the fragment's state within the activity and handling scenarios of its addition, removal, and replacement.