SharedPreferences for key-value in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the SharedPreferences package.

Flutter

import 'package:[1]/shared_preferences.dart';

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

Ashared_preferences

Bflutter

Cprefs

Dstorage

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect package names like 'flutter' or 'prefs'.

Forgetting to import the package.

The correct package name to import SharedPreferences is shared_preferences.

2fill in blank

medium

Complete the code to get an instance of SharedPreferences asynchronously.

Flutter

final prefs = await SharedPreferences.[1]();

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

Ainstance

BgetInstance

Cinit

Dload

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'instance' or 'init' which do not exist.

Not using await for the asynchronous call.

The method to get SharedPreferences instance is getInstance().

3fill in blank

hard

Fix the error in saving a string value with key 'username'.

Flutter

await prefs.[1]('username', 'Alice');

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

AputString

BsaveString

CsetString

DstoreString

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like 'saveString' or 'putString'.

Confusing with other storage APIs.

The correct method to save a string is setString.

4fill in blank

hard

Fill both blanks to read a string value for key 'username' with a default fallback.

Flutter

String username = prefs.[1]('username') ?? [2];

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

AgetString

B'Guest'

C'Anonymous'

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' instead of 'getString'.

Not providing a default value causing null errors.

Use getString to read the string and provide a default like 'Guest' if null.

5fill in blank

hard

Fill all three blanks to remove a key and check if it was removed successfully.

Flutter

bool removed = await prefs.[1]('username');
if (removed) {
  print('[2] was removed');
} else {
  print('[3] not found');
}

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

Aremove

Busername

CKey

DUser

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names like 'delete'.

Using incorrect key names in messages.

The method to remove a key is remove. The key name is username. The message uses 'Key' to indicate the key was not found.

Practice

1. What is the main purpose of using SharedPreferences in a Flutter app?

easy

A. To save small key-value data that persists after the app closes

B. To create complex database tables

C. To design the app's user interface

D. To handle network requests

Solution

1. Step 1: Understand SharedPreferences role

   SharedPreferences is designed to store simple data like settings or flags in key-value pairs.

2. Step 2: Compare with other options

   Options A, B, and C relate to databases, UI, and networking, which are not the purpose of SharedPreferences.

3. Final Answer:

   To save small key-value data that persists after the app closes -> Option A

4. Quick Check:

   SharedPreferences = persistent small key-value storage [OK]

Hint: Remember: SharedPreferences stores simple data persistently [OK]

Common Mistakes:

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

2. Which of the following is the correct way to save a boolean value true with key isLoggedIn using SharedPreferences in Flutter?

easy

A. prefs.putBool('isLoggedIn', true);

B. prefs.saveBool('isLoggedIn', true);

C. prefs.storeBool('isLoggedIn', true);

D. prefs.setBool('isLoggedIn', true);

Solution

1. Step 1: Recall SharedPreferences method names

   The correct method to save a boolean is setBool.

2. Step 2: Check method correctness

   Options A, B, and D use incorrect method names that do not exist in SharedPreferences API.

3. Final Answer:

   prefs.setBool('isLoggedIn', true); -> Option D

4. Quick Check:

   Save boolean = setBool [OK]

Hint: Use setBool to save booleans in SharedPreferences [OK]

Common Mistakes:

• Using incorrect method names like saveBool or putBool
• Forgetting to await async calls
• Confusing setBool with setString

3. Given the following Flutter code snippet, what will be printed?

final prefs = await SharedPreferences.getInstance();
await prefs.setInt('counter', 5);
int count = prefs.getInt('counter') ?? 0;
print(count);

medium

A. 0

B. null

C. 5

D. Error

Solution

1. Step 1: Analyze saving the value

   The code saves integer 5 with key 'counter' using setInt.

2. Step 2: Analyze reading the value

   It reads the value with getInt. Since 'counter' exists, it returns 5, not the default 0.

3. Final Answer:

   5 -> Option C

4. Quick Check:

   Saved int 5, getInt returns 5 [OK]

Hint: getInt returns saved value or default if missing [OK]

Common Mistakes:

• Assuming getInt returns null instead of default
• Confusing setInt with setString
• Forgetting to await setInt

4. What is wrong with this Flutter code that tries to save a string in SharedPreferences?

final prefs = SharedPreferences.getInstance();
prefs.setString('username', 'Alice');

medium

A. setString method does not exist

B. Missing await before getInstance()

C. Key 'username' cannot be a string

D. Cannot save strings in SharedPreferences

Solution

1. Step 1: Check getInstance usage

   getInstance() returns a Future, so it must be awaited or handled asynchronously.

2. Step 2: Check setString call

   Calling setString on a Future object (not the SharedPreferences instance) causes error.

3. Final Answer:

   Missing await before getInstance() -> Option B

4. Quick Check:

   Always await SharedPreferences.getInstance() [OK]

Hint: Always await getInstance() before using prefs [OK]

Common Mistakes:

• Not awaiting getInstance()
• Calling setString on Future instead of instance
• Confusing async calls with sync

5. You want to save a user's theme preference as a string ('light' or 'dark') and a flag if notifications are enabled (boolean). Which of the following code snippets correctly saves both values using SharedPreferences in Flutter?

hard

A. final prefs = await SharedPreferences.getInstance();
await prefs.setString('theme', 'dark');
await prefs.setBool('notifications', true);

B. final prefs = SharedPreferences.getInstance();
prefs.setString('theme', 'dark');
prefs.setBool('notifications', true);

C. final prefs = await SharedPreferences.getInstance();
prefs.setInt('theme', 'dark');
prefs.setBool('notifications', true);

D. final prefs = await SharedPreferences.getInstance();
await prefs.setInt('theme', 1);
await prefs.setBool('notifications', 'true');

Solution

1. Step 1: Check async usage

   SharedPreferences.getInstance() must be awaited to get the instance before use.

2. Step 2: Check method calls and types

   setString saves the theme string correctly; setBool saves the boolean flag correctly. Both use await for async calls.

3. Step 3: Identify errors in other options

   final prefs = SharedPreferences.getInstance(); prefs.setString('theme', 'dark'); prefs.setBool('notifications', true); misses await on getInstance and set methods; final prefs = await SharedPreferences.getInstance(); prefs.setInt('theme', 'dark'); prefs.setBool('notifications', true); uses setInt('theme', 'dark') causing type error ('dark' not int); final prefs = await SharedPreferences.getInstance(); await prefs.setInt('theme', 1); await prefs.setBool('notifications', 'true'); uses wrong types (setInt for string, boolean as string).

4. Final Answer:

   final prefs = await SharedPreferences.getInstance(); await prefs.setString('theme', 'dark'); await prefs.setBool('notifications', true); -> Option A

5. Quick Check:

   Await getInstance and setX methods with correct types [OK]

Hint: Await all async SharedPreferences calls with correct types [OK]

Common Mistakes:

• Not awaiting async calls
• Using wrong data types for values
• Saving booleans as strings