SavedStateHandle in Android Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is SavedStateHandle in Android Kotlin?

SavedStateHandle is a class that helps you save and restore UI-related data in ViewModels during process death or configuration changes, like screen rotations.

beginner

How do you get a SavedStateHandle instance inside a ViewModel?

You receive it as a constructor parameter when you create your ViewModel by extending ViewModel and using SavedStateViewModelFactory or by viewModels() with saved state support.

beginner

How do you save a value using SavedStateHandle?

Use the set(key, value) method. For example, savedStateHandle.set("count", 5) saves the number 5 with the key "count".

beginner

How do you retrieve a saved value from SavedStateHandle?

Use the get<T>(key) method. For example, savedStateHandle.get<Int>("count") returns the saved integer or null if not found.

intermediate

Why is SavedStateHandle better than just using onSaveInstanceState in Activities?

SavedStateHandle works inside ViewModels, keeping UI data separate from UI controllers. It survives process death and configuration changes without cluttering Activity or Fragment code.

What is the main purpose of SavedStateHandle in Android Kotlin?

A To save and restore UI-related data in ViewModels

B To handle network requests

C To manage database connections

D To create UI layouts

SavedStateHandle is designed to save and restore UI-related data inside ViewModels.

How do you typically receive a SavedStateHandle in a ViewModel?

A As a constructor parameter

B By calling a static method

C By accessing a global variable

D By inflating a layout

SavedStateHandle is passed as a constructor parameter to the ViewModel.

Which method saves a value in SavedStateHandle?

A put(key, value)

B set(key, value)

C save(key, value)

D store(key, value)

The correct method to save data is set(key, value).

What happens to data saved in SavedStateHandle when the app process is killed and restarted?

A Data is lost

B Data is sent to the server

C Data is saved to a file

D Data is restored automatically

SavedStateHandle restores data automatically after process death.

Which Android component benefits most from using SavedStateHandle?

A Service

B Activity

C ViewModel

D BroadcastReceiver

SavedStateHandle is designed to be used inside ViewModels.

Explain how SavedStateHandle helps preserve UI state in Android apps.

Think about how your app remembers data after screen rotation or app restart.

Describe the steps to use SavedStateHandle in a ViewModel to save a counter value.

Imagine you want to keep track of a number even if the app restarts.

Practice

1.

What is the main purpose of SavedStateHandle in Android Kotlin?

easy

A. To save and restore small UI-related data automatically during configuration changes

B. To manage database connections

C. To handle network requests

D. To create UI layouts dynamically

Solution

1. Step 1: Understand the role of SavedStateHandle

   SavedStateHandle is designed to save small pieces of data like UI state during configuration changes such as screen rotations.

2. Step 2: Compare with other options

   Options A, B, and D relate to network requests, database connections, and UI layout creation, which are not the purpose of SavedStateHandle.

3. Final Answer:

   To save and restore small UI-related data automatically during configuration changes -> Option A

4. Quick Check:

   SavedStateHandle saves UI state = C [OK]

Hint: Remember: SavedStateHandle saves UI data on config changes [OK]

Common Mistakes:

• Confusing SavedStateHandle with database or network management
• Thinking it manages large data or files
• Assuming it creates UI layouts

2.

Which of the following is the correct way to store a value "username" in SavedStateHandle named savedStateHandle?

?

easy

A. savedStateHandle.put("username", "John")

B. savedStateHandle.set("username", "John")

C. savedStateHandle.save("username", "John")

D. savedStateHandle.store("username", "John")

Solution

1. Step 1: Recall SavedStateHandle API methods

   The correct method to store data is set(key, value).

2. Step 2: Check method names in options

   Only savedStateHandle.set("username", "John") uses set, others use incorrect method names.

3. Final Answer:

   savedStateHandle.set("username", "John") -> Option B

4. Quick Check:

   Use set() to store data = A [OK]

Hint: Use set() to save data in SavedStateHandle [OK]

Common Mistakes:

• Using put(), save(), or store() which do not exist
• Confusing with SharedPreferences methods
• Forgetting to use quotes around keys

3.

Given the code below, what will be the output of println(savedStateHandle.get<String>("name"))?

val savedStateHandle = SavedStateHandle()
savedStateHandle.set("name", "Alice")
savedStateHandle.set("age", 30)
savedStateHandle.set("name", "Bob")

medium

A. null

B. Alice

C. Bob

D. 30

Solution

1. Step 1: Analyze the set operations

   The key "name" is first set to "Alice", then overwritten with "Bob".

2. Step 2: Determine the value returned by get

   Getting "name" returns the latest value, which is "Bob".

3. Final Answer:

   Bob -> Option C

4. Quick Check:

   Last set value returned = A [OK]

Hint: Last set value for a key is returned by get() [OK]

Common Mistakes:

• Assuming first set value is returned
• Confusing key names
• Expecting numeric value for string key

4.

Identify the error in the following code snippet using SavedStateHandle:

val savedStateHandle = SavedStateHandle()
savedStateHandle.set("count", 10)
val count: String = savedStateHandle.get("count") ?: "0"
println(count)

medium

A. println() cannot print variables

B. Missing key in get() method

C. SavedStateHandle cannot store Int values

D. Type mismatch: trying to assign Int to String without conversion

Solution

1. Step 1: Check variable types

   The value stored is Int (10), but retrieved as String without conversion.

2. Step 2: Understand Kotlin type safety

   Assigning Int to String variable causes a type mismatch error.

3. Final Answer:

   Type mismatch: trying to assign Int to String without conversion -> Option D

4. Quick Check:

   Type mismatch error = D [OK]

Hint: Match types when getting values from SavedStateHandle [OK]

Common Mistakes:

• Ignoring type mismatch errors
• Assuming automatic type conversion
• Thinking SavedStateHandle only stores strings

5.

You want to save a user's score in SavedStateHandle and restore it after a configuration change. Which approach correctly ensures the score is saved and retrieved safely?

class ScoreViewModel(private val savedStateHandle: SavedStateHandle) : ViewModel() {
    fun saveScore(score: Int) {
        // What to do here?
    }
    fun getScore(): Int {
        // What to do here?
    }
}

hard

A. saveScore: savedStateHandle.set("score", score)
getScore: savedStateHandle.get<Int>("score") ?: 0

B. saveScore: savedStateHandle.put("score", score)
getScore: savedStateHandle.get("score") as Int

C. saveScore: savedStateHandle.save("score", score)
getScore: savedStateHandle.get("score") ?: 0

D. saveScore: savedStateHandle.set("score", score.toString())
getScore: savedStateHandle.get<String>("score")?.toInt() ?: 0

Solution

1. Step 1: Use correct methods to save and get data

   Use set to save and get<Int> to retrieve with a default fallback.

2. Step 2: Validate type safety and default value

   saveScore: savedStateHandle.set("score", score) getScore: savedStateHandle.get<Int>("score") ?: 0 uses correct method names and safely returns 0 if no score is saved.

3. Final Answer:

   saveScore: savedStateHandle.set("score", score) getScore: savedStateHandle.get<Int>("score") ?: 0 -> Option A

4. Quick Check:

   Use set() and get<Int>() with default = B [OK]

Hint: Always use set() and get<Type>() with default fallback [OK]

Common Mistakes:

• Using non-existent methods like put() or save()
• Storing Int as String unnecessarily
• Not providing default value on get()