Fragment Lifecycle Scenarios Explained

1. Fragment Lifecycle with FragmentManager

Below are the examples with their corresponding lifecycle charts for clarity.

---

a. Add Fragment Without addToBackStack

supportFragmentManager
	.beginTransaction()
	.add(R.id.fragment_container,FragmentA())
	.commit()

Scenario: You add FragmentA without saving it to the back stack.

FragmentA Lifecycle	State
onAttach()	Fragment is attached to the host.
onCreate()	Fragment is initialized.
onCreateView()	Fragment’s UI is created.
onStart()	Fragment becomes visible.
onResume()	Fragment is active.

Behavior:

• Adding a new fragment (e.g., FragmentB) destroys FragmentA’s view but keeps it attached in memory.
• No back stack. Pressing the back button exits the app.

---

b. Add Fragment With addToBackStack

supportFragmentManager
	.beginTransaction()     
	.add(R.id.fragment_container, FragmentA())     
	.addToBackStack(null)     
	.commit()

Scenario: FragmentA is added and saved to the back stack.

FragmentA Lifecycle	State
onAttach()	Fragment is attached.
onCreate()	Fragment is initialized.
onCreateView()	Fragment’s UI is created.
onStart()	Fragment becomes visible.
onResume()	Fragment is active.

Behavior:

• Adding a new fragment (e.g., FragmentB):
  • FragmentA calls onPause and onStop but remains in memory.
• Pressing back restores FragmentA from memory.

---

c. Replace Fragment Without addToBackStack

supportFragmentManager
	.beginTransaction()     
	.replace(R.id.fragment_container, FragmentA())     
	.commit()

Scenario: Replace any existing fragment with FragmentA. Old fragments are destroyed.

Old Fragment Lifecycle	New Fragment (FragmentA)
onPause()	onAttach()
onStop()	onCreate()
onDestroyView()	onCreateView()
onDestroy()	onStart()
onDetach()	onResume()

Behavior:

• Old fragments are fully destroyed.
• No back stack. Pressing the back button exits the app.

---

d. Replace Fragment With addToBackStack

supportFragmentManager
	.beginTransaction()     
	.replace(R.id.fragment_container, FragmentA())     
	.addToBackStack(null)     
	.commit()

Scenario: Replace the old fragment with FragmentA and save the old one to the back stack.

Old Fragment Lifecycle	New Fragment (FragmentA)
onPause()	onAttach()
onStop()	onCreate()
onDestroyView()	onCreateView()
(Retained in memory)	onStart()
	onResume()

Behavior:

• Old fragments are paused and stopped, but not destroyed.
• Pressing back removes FragmentA and restores the old fragment.

---

2. NavController with NavGraph

---

a. Navigate to a New Fragment

findNavController().navigate(R.id.action_fragmentA_to_fragmentB)

Scenario: FragmentA navigates to FragmentB via the NavController.

FragmentA Lifecycle	FragmentB Lifecycle
onPause()	onAttach()
onStop()	onCreate()
onDestroyView()	onCreateView()
(Removed from memory)	onStart()
	onResume()

Behavior:

• FragmentA is removed from memory entirely.
• FragmentB starts its lifecycle from onAttach().

---

b. Back Navigation

When the back button is pressed:

• FragmentB Lifecycle:
  • onPause, onStop, onDestroyView, onDestroy, and onDetach.
• FragmentA Lifecycle:
  • Recreated from onCreateView, followed by onStart and onResume.

FragmentB Lifecycle	FragmentA Lifecycle
onPause()	onCreateView()
onStop()	onStart()
onDestroyView()	onResume()
onDestroy()
onDetach()

---

c. Removing a Fragment

If FragmentB is removed manually:

• FragmentB Lifecycle:
  • Fully destroyed: onPause, onStop, onDestroyView, onDestroy, and onDetach.
• FragmentA Lifecycle:
  • Brought back into the foreground: onCreateView, onStart, and onResume.

---

Comparison of NavController vs. FragmentManager

Feature	FragmentManager	NavController
Old Fragment Behavior	Retained in memory with addToBackStack.	Removed from memory entirely.
Back Stack Handling	Manual with addToBackStack.	Automatic back stack handling.
Lifecycle Resumption	Old fragment resumes lifecycle.	Old fragment is recreated.
Ease of Use	More control, more code.	Simplified navigation.