Lists, Maps, and Sets in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output of this Flutter List display?

Consider this Flutter code snippet that displays a list of names in a ListView. What will be shown on the screen?

Flutter

List<String> names = ['Anna', 'Bob', 'Cara'];

ListView(
  children: names.map((name) => Text(name)).toList(),
)

A A single Text widget showing 'AnnaBobCara' concatenated

B An empty screen with no text

C A vertical list showing: Anna, Bob, Cara each on its own line

D A runtime error because ListView children must be widgets

💡 Hint

Think about how map and toList create widgets for each name.

The map function creates a Text widget for each name. The ListView shows these widgets vertically.

🧠 Conceptual

intermediate

How does a Dart Map store data?

In Dart, what is the main characteristic of a Map collection?

A It stores only integer values indexed by position

B It stores only unique values without keys

C It stores ordered elements like a list

D It stores key-value pairs where keys are unique and values can be any type

💡 Hint

Think about how you look up a phone number by a person's name.

A Map stores data as pairs: each key is unique and maps to a value.

📝 Syntax

advanced

What error does this Dart Set code cause?

What error will this Dart code produce? Set numbers = {1, 2, 3, 3, 4}; print(numbers.length);

Flutter

Set<int> numbers = {1, 2, 3, 3, 4};
print(numbers.length);

A Prints 4 because duplicates are ignored in sets

B Prints 5 because duplicates are allowed in sets

C SyntaxError because duplicate values are not allowed in set literals

D Runtime error because sets cannot contain integers

💡 Hint

Remember what a set means in math: no duplicates.

Sets automatically remove duplicates, so the length counts unique values only.

❓ lifecycle

advanced

How does Flutter rebuild widgets when a List changes?

If you update a List used in a Flutter widget's build method, what triggers the UI to update?

A Calling setState() to notify Flutter to rebuild the widget

B Changing the List automatically rebuilds the UI without extra code

C You must manually refresh the screen outside Flutter

D Flutter rebuilds only when the app restarts

💡 Hint

Think about how Flutter knows when to redraw the screen.

Flutter rebuilds widgets when setState() is called to notify changes.

🔧 Debug

expert

Why does this Flutter Map access cause an error?

Given this Dart Map: Map ages = {'Alice': 30, 'Bob': 25}; What error occurs when running: print(ages['Cara']!);

Flutter

Map<String, int> ages = {'Alice': 30, 'Bob': 25};
print(ages['Cara']!);

A Prints null because 'Cara' is not in the map

B Throws a runtime error because 'Cara' key does not exist and ! forces non-null

C Syntax error because ! cannot be used with map access

D Prints 0 because missing keys default to zero

💡 Hint

Consider what happens when you force a null value to be non-null.

The ! operator asserts the value is not null, but 'Cara' key is missing, so it throws an error.