SharedPreferences for key-value in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output after saving and reading a value?

Consider this Flutter code snippet that saves a string to SharedPreferences and then reads it back. What will be printed in the console?

Flutter

final prefs = await SharedPreferences.getInstance();
await prefs.setString('username', 'Alice');
final name = prefs.getString('username');
print(name);

A Alice

B Throws an exception

C '' (empty string)

D null

💡 Hint

Remember that setString stores the value and getString retrieves it by the same key.

The code saves the string 'Alice' under the key 'username'. Then it reads it back with getString using the same key, so it prints 'Alice'.

❓ lifecycle

intermediate

When should you initialize SharedPreferences in a Flutter app?

In a Flutter app, when is the best time to call SharedPreferences.getInstance() to ensure data is ready for use?

A In the main() function before runApp()

B After the widget is disposed

C Inside the build() method of a widget

D In the initState() method of a StatefulWidget

💡 Hint

Think about when you want to load data once when the widget is created.

Calling SharedPreferences.getInstance() in initState() ensures the preferences are loaded once when the widget starts, avoiding repeated calls in build().

🔧 Debug

advanced

Why does this code fail to save the value?

Look at this Flutter code snippet. Why does it not save the integer value as expected?

Flutter

void saveScore() async {
  final prefs = await SharedPreferences.getInstance();
  prefs.setInt('score', 100);
}

A The key 'score' is reserved and cannot be used

B setInt() does not exist in SharedPreferences

C SharedPreferences.getInstance() returns a Future, so it must be awaited

D The method saveScore() must be synchronous

💡 Hint

Check how you handle asynchronous calls in Dart.

SharedPreferences.getInstance() returns a Future, so you must await it to get the instance before calling setInt.

🧠 Conceptual

advanced

What happens if you try to read a non-existent key?

If you call prefs.getString('nonexistentKey') on SharedPreferences where the key was never saved, what will be the result?

A It throws a KeyNotFoundException

B It returns null

C It returns an empty string ''

D It returns the string 'null'

💡 Hint

Think about how Dart handles missing keys in maps or similar APIs.

SharedPreferences returns null when a key does not exist, so getString returns null if the key is missing.

❓ navigation

expert

How to update UI after SharedPreferences value changes?

You saved a value in SharedPreferences and want your Flutter widget to update immediately to show the new value. Which approach works best?

A Use setState() after reading the updated value from SharedPreferences

B Restart the app to reload SharedPreferences

C Use a StreamBuilder directly on SharedPreferences

D SharedPreferences automatically notifies widgets to rebuild

💡 Hint

Think about how Flutter widgets update when data changes.

SharedPreferences does not notify widgets automatically. You must read the new value and call setState() to rebuild the widget with updated data.