SharedPreferences / DataStore in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get an instance of SharedPreferences in an Activity.

Android Kotlin

val sharedPrefs = getSharedPreferences([1], Context.MODE_PRIVATE)

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

A"my_prefs"

Bthis

C"prefs"

DMODE_PRIVATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable instead of a string literal for the name.

Passing the mode as the first argument.

You need to provide the name of the SharedPreferences file as a string. "my_prefs" is a common example.

2fill in blank

medium

Complete the code to save a string value "user_name" in SharedPreferences.

Android Kotlin

sharedPrefs.edit().putString([1], "John").apply()

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

A"name"

B"user_name"

CuserName

D"username"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable instead of a string literal for the key.

Misspelling the key string.

The key used to store the string should be "user_name" as specified.

3fill in blank

hard

Fix the error in the code to read an integer value "age" from SharedPreferences with default 0.

Android Kotlin

val age = sharedPrefs.getInt([1], 0)

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

Aage

BdefaultAge

C0

D"age"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable instead of a string literal for the key.

Passing the default value as the key.

The key must be a string literal "age" to correctly retrieve the value.

4fill in blank

hard

Fill both blanks to create a DataStore instance named "user_prefs" in a Context.

Android Kotlin

val dataStore: DataStore<Preferences> = context.[1](name = [2])

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

AcreateDataStore

B"user_prefs"

C"prefs"

DdataStore

Attempts:

3 left

💡 Hint

Common Mistakes

Using an incorrect function name.

Passing the name without quotes.

Use createDataStore function with the name "user_prefs" to create the DataStore instance.

5fill in blank

hard

Fill all three blanks to read a string preference "email" from DataStore with default "".

Android Kotlin

val emailFlow: Flow<String> = dataStore.data.map { preferences ->
  preferences[[1]] ?: [2]
}

val EMAIL_KEY = stringPreferencesKey([3])

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

AEMAIL_KEY

B""

C"email"

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Using the string "email" directly instead of the key variable.

Using null instead of empty string as default.

EMAIL_KEY is the key used to access the preference. The default value is an empty string "". The key name is "email".

Practice

1. What is the main purpose of SharedPreferences in Android development?

easy

A. To handle network requests and responses

B. To create complex database tables for large data storage

C. To save small amounts of key-value data persistently on the device

D. To design user interface layouts

Solution

1. Step 1: Understand SharedPreferences role

   SharedPreferences is designed to store small amounts of data as key-value pairs persistently on the device.

2. Step 2: Compare with other options

   Options B, C, and D describe unrelated tasks like databases, networking, and UI design, which are not the purpose of SharedPreferences.

3. Final Answer:

   To save small amounts of key-value data persistently on the device -> Option C

4. Quick Check:

   SharedPreferences = small persistent key-value storage [OK]

Hint: Remember SharedPreferences stores simple key-value pairs [OK]

Common Mistakes:

• Confusing SharedPreferences with databases
• Thinking SharedPreferences handles UI or network
• Assuming SharedPreferences stores large files

2. Which of the following is the correct way to get a SharedPreferences instance in Kotlin inside an Activity?

easy

A. val prefs = SharedPreferences("my_prefs")

B. val prefs = getSharedPreferences("my_prefs", Context.MODE_PRIVATE)

C. val prefs = SharedPreferences.getInstance("my_prefs")

D. val prefs = getPreferences("my_prefs")

Solution

1. Step 1: Recall correct method to get SharedPreferences

   The correct method is to call getSharedPreferences(name, mode) on a Context, passing the name and mode.

2. Step 2: Analyze options

   val prefs = getSharedPreferences("my_prefs", Context.MODE_PRIVATE) uses the correct method. Options A, C, and D are invalid constructors or methods. val prefs = getPreferences("my_prefs") uses getPreferences which does not take a name parameter.

3. Final Answer:

   val prefs = getSharedPreferences("my_prefs", Context.MODE_PRIVATE) -> Option B

4. Quick Check:

   Use getSharedPreferences(name, mode) to get prefs [OK]

Hint: Use getSharedPreferences with name and mode inside Activity [OK]

Common Mistakes:

• Trying to instantiate SharedPreferences directly
• Using getPreferences with a name parameter
• Confusing method names or parameters

3. What will be the output of this Kotlin code snippet using SharedPreferences?

val prefs = getSharedPreferences("settings", Context.MODE_PRIVATE)
val editor = prefs.edit()
editor.putString("username", "Alice")
editor.apply()
val name = prefs.getString("username", "Unknown")
println(name)

medium

A. null

B. Unknown

C. Compilation error

D. Alice

Solution

1. Step 1: Store value in SharedPreferences

   The code puts the string "Alice" with key "username" and applies the changes asynchronously.

2. Step 2: Retrieve stored value

   Then it retrieves the value for "username"; since it was stored, it returns "Alice" instead of the default "Unknown".

3. Final Answer:

   Alice -> Option D

4. Quick Check:

   Stored value retrieved correctly = Alice [OK]

Hint: Stored keys return saved value, else default [OK]

Common Mistakes:

• Forgetting to call apply() or commit()
• Expecting default value when key exists
• Confusing synchronous and asynchronous apply

4. Identify the error in this Kotlin code using DataStore to save a boolean value:

val dataStore = context.createDataStore(name = "settings")
fun saveFlag(flag: Boolean) {
  dataStore.edit { preferences ->
    preferences[booleanPreferencesKey("flag")] = flag
  }
}

medium

A. Missing 'suspend' modifier on the saveFlag function

B. Missing commit() call after edit block

C. booleanPreferencesKey should be replaced with stringPreferencesKey

D. DataStore cannot store boolean values

Solution

1. Step 1: Check DataStore function modifiers

   The function saveFlag must be marked suspend because it calls dataStore.edit(), which is a suspend function.

2. Step 2: Verify other code parts

   The createDataStore call is correct. The edit block commits changes automatically. Using booleanPreferencesKey is correct for boolean values. DataStore supports boolean values.

3. Final Answer:

   Missing 'suspend' modifier on the saveFlag function -> Option A

4. Quick Check:

   DataStore edit requires suspend function [OK]

Hint: DataStore edit calls require suspend functions [OK]

Common Mistakes:

• Missing 'suspend' modifier on saveFlag function
• Forgetting suspend modifier on save function
• Confusing preference key types

5. You want to migrate existing user settings from SharedPreferences to DataStore in a Kotlin app. Which approach correctly handles this migration?

hard

A. Use SharedPreferencesMigration with DataStore to copy data automatically on first access

B. Manually read all SharedPreferences keys and write them to DataStore every app start

C. Delete SharedPreferences and start fresh with DataStore without migration

D. Use SharedPreferences.edit() inside DataStore's edit block

Solution

1. Step 1: Understand migration support in DataStore

   DataStore provides a built-in SharedPreferencesMigration class to migrate data automatically from SharedPreferences on first DataStore access.

2. Step 2: Evaluate other options

   Manually read all SharedPreferences keys and write them to DataStore every app start is inefficient and error-prone. Delete SharedPreferences and start fresh with DataStore without migration loses user data. Use SharedPreferences.edit() inside DataStore's edit block is invalid because SharedPreferences and DataStore APIs are separate and cannot be mixed inside edit blocks.

3. Final Answer:

   Use SharedPreferencesMigration with DataStore to copy data automatically on first access -> Option A

4. Quick Check:

   Use SharedPreferencesMigration for smooth migration [OK]

Hint: Use SharedPreferencesMigration for easy migration [OK]

Common Mistakes:

• Trying manual migration every app start
• Deleting old preferences losing data
• Mixing SharedPreferences API inside DataStore