Lifecycle awareness in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ lifecycle

intermediate

What is the output when the Activity is rotated?

Consider this Android Activity code snippet. What will be printed in the log when the device is rotated (causing configuration change)?

Android Kotlin

class MainActivity : AppCompatActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    Log.d("Lifecycle", "onCreate called")
  }
  override fun onDestroy() {
    super.onDestroy()
    Log.d("Lifecycle", "onDestroy called")
  }
}

A onDestroy called followed by onCreate called

B Only onCreate called

C Only onDestroy called

D Neither onCreate nor onDestroy called

💡 Hint

Think about what happens to an Activity during a configuration change like rotation.

When the device rotates, the current Activity is destroyed and recreated. So onDestroy is called first, then onCreate is called again.

❓ ui_behavior

intermediate

Which lifecycle method is best to start a camera preview?

You want to start the camera preview when the user can see the app screen. Which lifecycle method should you use?

A onStart()

B onCreate()

C onPause()

D onResume()

💡 Hint

Consider when the app is fully visible and interactive.

onResume() is called when the Activity is in the foreground and ready for user interaction, so it's the best place to start camera preview.

🔧 Debug

advanced

Why does this app crash on rotation?

This Activity crashes when rotated. What is the cause?

Android Kotlin

class MainActivity : AppCompatActivity() {
  private lateinit var textView: TextView
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    textView = findViewById(R.id.textView)
    textView.text = "Hello"
  }
}

A textView is null because it is not declared

B Missing call to super.onCreate()

C textView is used before setContentView, so it is not initialized

D setContentView should be called after onCreate

💡 Hint

Think about when views are available after setContentView.

textView is accessed before setContentView, so it is not yet linked to the layout and causes a crash.

❓ navigation

advanced

What happens to the Activity stack after this navigation?

In an app, MainActivity starts DetailActivity with this code: startActivity(Intent(this, DetailActivity::class.java)) finish() What is the state of the Activity stack after this runs?

A MainActivity is removed, DetailActivity is on top

B Both MainActivity and DetailActivity are in the stack

C Only MainActivity remains in the stack

D DetailActivity is removed immediately

💡 Hint

Consider what finish() does after starting a new Activity.

finish() removes MainActivity from the stack, so only DetailActivity remains on top.

🧠 Conceptual

expert

What is the correct order of lifecycle callbacks when an Activity goes to background and then returns?

Put these lifecycle methods in the order they are called when the user presses Home (app goes to background) and then returns to the app.

A 1,2,4,3,5

B 1,2,3,4,5

C 2,1,3,4,5

D 1,3,2,4,5

💡 Hint

Remember the lifecycle flow when app goes background and foreground.

When going to background: onPause then onStop. When returning: onRestart, onStart, onResume.