Saving instance state in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to save a string value in the instance state bundle.

Android Kotlin

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  outState.putString("KEY_NAME", [1])
}

Drag options to blanks, or click blank then click option'

AgetName()

Bname

Cthis.name

DsavedName

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method call instead of the variable.

Using a variable name that does not exist.

You save the variable name into the bundle with putString.

2fill in blank

medium

Complete the code to restore the saved string value from the instance state bundle.

Android Kotlin

override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  if (savedInstanceState != null) {
    name = savedInstanceState.[1]("KEY_NAME") ?: ""
  }
}

Drag options to blanks, or click blank then click option'

AgetString

BgetCharSequence

CgetInt

DgetSerializable

Attempts:

3 left

💡 Hint

Common Mistakes

Using getInt which returns an integer, not a string.

Using getSerializable which is for objects, not strings.

Use getString to retrieve the saved string from the bundle.

3fill in blank

hard

Fix the error in saving an integer counter in the instance state bundle.

Android Kotlin

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  outState.[1]("COUNTER", counter)
}

Drag options to blanks, or click blank then click option'

AputString

BputBoolean

CputSerializable

DputInt

Attempts:

3 left

💡 Hint

Common Mistakes

Using putString for an integer value causes a type error.

Using putSerializable unnecessarily complicates saving simple types.

Use putInt to save an integer value in the bundle.

4fill in blank

hard

Fill both blanks to restore an integer counter and provide a default value if missing.

Android Kotlin

override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  counter = savedInstanceState?.[1]("COUNTER") ?: [2]
}

Drag options to blanks, or click blank then click option'

AgetInt

B0

C1

DgetString

Attempts:

3 left

💡 Hint

Common Mistakes

Using getString to get an integer causes errors.

Using a default value other than zero without reason.

Use getInt to get the integer and 0 as the default value if none is saved.

5fill in blank

hard

Fill all three blanks to save and restore a boolean flag in the instance state.

Android Kotlin

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  outState.[1]("FLAG", flag)
}

override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  flag = savedInstanceState?.[2]("FLAG") ?: [3]
}

Drag options to blanks, or click blank then click option'

AputBoolean

BgetBoolean

Cfalse

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using putInt or putString for boolean values.

Using true as default without reason.

Use putBoolean to save, getBoolean to restore, and false as the default flag value.

Practice

1. What is the main purpose of onSaveInstanceState in Android Kotlin apps?

easy

A. To initialize UI components when the app starts

B. To permanently store data in a database

C. To save UI data temporarily during events like screen rotation

D. To handle user input events like button clicks

Solution

1. Step 1: Understand the role of onSaveInstanceState

   This method is called before an activity might be destroyed, such as during screen rotation, to save temporary UI data.

2. Step 2: Differentiate from other data storage methods

   Permanent storage like databases is not handled here; onSaveInstanceState is for short-term state saving only.

3. Final Answer:

   To save UI data temporarily during events like screen rotation -> Option C

4. Quick Check:

   onSaveInstanceState saves temporary UI state [OK]

Hint: Remember: onSaveInstanceState saves temporary UI data [OK]

Common Mistakes:

• Confusing onSaveInstanceState with permanent storage
• Thinking it initializes UI components
• Assuming it handles user input events

2. Which of the following is the correct way to save a string value "username" in onSaveInstanceState?

easy

A. bundle.putString("username", username)

B. outState.putString("username", username)

C. savedInstanceState.putString("username", username)

D. state.putString("username", username)

Solution

1. Step 1: Identify the correct parameter name in onSaveInstanceState

   The Bundle parameter is named outState in onSaveInstanceState method.

2. Step 2: Use the correct method to save a string

   Use outState.putString(key, value) to save the string value.

3. Final Answer:

   outState.putString("username", username) -> Option B

4. Quick Check:

   Use outState to save data in onSaveInstanceState [OK]

Hint: Use outState.putString() inside onSaveInstanceState [OK]

Common Mistakes:

• Using savedInstanceState inside onSaveInstanceState
• Using undefined variable names like bundle or state
• Confusing parameter names in lifecycle methods

3. Given this code snippet inside an Activity:

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  outState.putInt("score", 10)
}

override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  val score = savedInstanceState?.getInt("score") ?: 0
  println(score)
}

What will be printed after a screen rotation?

medium

A. Crash due to NullPointerException

B. 0

C. null

D. 10

Solution

1. Step 1: Understand saving the score in onSaveInstanceState

   The score 10 is saved in the outState bundle before the activity is destroyed.

2. Step 2: Restore score in onCreate after rotation

   savedInstanceState contains the saved bundle, so getInt("score") returns 10, not null or 0.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Saved state restores score = 10 after rotation [OK]

Hint: savedInstanceState?.getInt() returns saved value or default [OK]

Common Mistakes:

• Assuming savedInstanceState is always null
• Forgetting to call super.onSaveInstanceState
• Expecting 0 instead of restored value

4. What is wrong with this code snippet for saving instance state?

override fun onSaveInstanceState(outState: Bundle) {
  outState.putInt("count", count)
}

override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  val count = savedInstanceState?.getInt("count") ?: 0
}

medium

A. Missing call to super.onSaveInstanceState in onSaveInstanceState

B. Using wrong key name "count"

C. Not initializing count variable before saving

D. Not checking savedInstanceState for null in onCreate

Solution

1. Step 1: Check onSaveInstanceState method

   It lacks a call to super.onSaveInstanceState(outState), which is required to save default state.

2. Step 2: Verify other parts

   Key name "count" is consistent, count variable assumed initialized, and null check is done in onCreate.

3. Final Answer:

   Missing call to super.onSaveInstanceState in onSaveInstanceState -> Option A

4. Quick Check:

   Always call super.onSaveInstanceState [OK]

Hint: Always call super.onSaveInstanceState in override [OK]

Common Mistakes:

• Forgetting super call in onSaveInstanceState
• Using inconsistent keys for saving/restoring
• Ignoring null checks on savedInstanceState

5. You want to save a checkbox state and a user input text during screen rotation. Which approach correctly saves and restores both in an Activity?

hard

A. Save checkbox state and text in onSaveInstanceState using outState.putBoolean and outState.putString, then restore in onCreate using savedInstanceState?.getBoolean and getString

B. Save checkbox state only in onSaveInstanceState, restore text from a global variable

C. Save text in onPause and checkbox state in onStop, restore both in onResume

D. Use SharedPreferences to save checkbox and text, restore in onCreate

Solution

1. Step 1: Use onSaveInstanceState for temporary UI data

   Checkbox state (boolean) and text (string) should be saved in outState bundle in onSaveInstanceState.

2. Step 2: Restore saved data in onCreate

   Use savedInstanceState?.getBoolean and getString to restore checkbox and text after rotation.

3. Final Answer:

   Save checkbox state and text in onSaveInstanceState using outState.putBoolean and outState.putString, then restore in onCreate using savedInstanceState?.getBoolean and getString -> Option A

4. Quick Check:

   Use onSaveInstanceState and savedInstanceState for UI state [OK]

Hint: Save UI data in onSaveInstanceState, restore in onCreate [OK]

Common Mistakes:

• Using global variables that reset on rotation
• Saving data in lifecycle methods not meant for state
• Using persistent storage for temporary UI state