Saving instance state in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens to the TextView content after screen rotation?

Consider this Android Kotlin code snippet inside an Activity. The user types text into an EditText and clicks a button to copy it to a TextView. What will the TextView show after rotating the device screen?

Android Kotlin

class MainActivity : AppCompatActivity() {
  private lateinit var editText: EditText
  private lateinit var textView: TextView

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    editText = findViewById(R.id.editText)
    textView = findViewById(R.id.textView)

    findViewById<Button>(R.id.button).setOnClickListener {
      textView.text = editText.text.toString()
    }
  }
}

A The EditText content is lost but TextView keeps its text.

B The TextView keeps showing the copied text after rotation.

C The app crashes on rotation due to missing state handling.

D The TextView becomes empty after rotation.

💡 Hint

Think about what happens to Activity variables when the screen rotates without saving state.

By default, when the screen rotates, the Activity is destroyed and recreated. Without saving the TextView content in onSaveInstanceState and restoring it, the TextView resets to its initial empty state.

❓ lifecycle

intermediate

Which method is used to save UI state before Activity destruction?

In Android Kotlin, which lifecycle method should you override to save UI state before the Activity is destroyed (e.g., during rotation)?

A onSaveInstanceState(bundle: Bundle)

B onStop()

C onPause()

D onDestroy()

💡 Hint

This method receives a Bundle to store key-value pairs for restoration.

The onSaveInstanceState method is called before the Activity is destroyed to save transient UI state in a Bundle. This Bundle is passed back to onCreate or onRestoreInstanceState to restore the state.

📝 Syntax

advanced

What is the correct way to save a string in onSaveInstanceState?

Choose the correct Kotlin code snippet to save a string variable named 'userInput' into the Bundle in onSaveInstanceState.

Android Kotlin

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  // Save userInput here
}

A outState.put("input", userInput)

B outState.putString("input", userInput)

C outState["input"] = userInput

D outState.saveString("input", userInput)

💡 Hint

Use the Bundle method designed for strings.

The Bundle class has a method putString(key: String, value: String?) to save strings. Other options are invalid or do not exist.

🔧 Debug

advanced

Why does the restored TextView remain empty after rotation?

This code tries to restore a saved string to a TextView in onCreate but the TextView stays empty after rotation. What is the likely cause?

Android Kotlin

override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  setContentView(R.layout.activity_main)

  val textView = findViewById<TextView>(R.id.textView)
  val savedText = savedInstanceState?.getString("text")
  textView.text = savedText ?: ""
}

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  outState.putString("text", textView.text.toString())
}

A textView is not declared as a class property, so onSaveInstanceState cannot access it.

B The savedInstanceState Bundle is always null in onCreate.

C onSaveInstanceState is not called during rotation.

D The key "text" used in getString and putString do not match.

💡 Hint

Check variable scope and where textView is declared.

The textView variable used in onSaveInstanceState is undefined because it is declared only inside onCreate. This causes a runtime error or no value saved, so restoration fails.

🧠 Conceptual

expert

Why is saving instance state important in Android apps?

Select the best explanation why saving instance state is crucial for a good user experience in Android apps.

A It allows the app to run background tasks without interruption.

B It improves app startup speed by caching data permanently on disk.

C It preserves UI data during configuration changes like rotation, preventing data loss and user frustration.

D It automatically backs up user data to the cloud.

💡 Hint

Think about what happens when the screen rotates or the app is temporarily stopped.

Saving instance state helps keep temporary UI data intact during configuration changes like screen rotation, so users do not lose their input or progress.