Dart Maps - A Complete Beginner Guide with Examples

Map in Dart - Beginner's Complete Guide with Examples

If you are learning Dart (or Flutter), understanding Maps is crucial. Maps help us store data as key-value pairs, just like dictionaries in Python or HashMaps in Java.

What is a Map in Dart?

A Map in Dart is an object that associates keys to values. Both keys and values can be of any type (String, int, double, etc.).

Basic Syntax:


Map<KeyType, ValueType> mapName = {
  key1: value1,
  key2: value2,
};

Creating a Map in Dart

Example 1: Simple String Map


void main() {
  Map<String, String> countryCapital = {
    'India': 'New Delhi',
    'USA': 'Washington DC',
    'Japan': 'Tokyo',
  };

  print(countryCapital);
}

Output:


{India: New Delhi, USA: Washington DC, Japan: Tokyo}

Accessing Map Values

You can access a value using its key.


void main() {
  Map<String, String> countryCapital = {
    'India': 'New Delhi',
    'USA': 'Washington DC',
    'Japan': 'Tokyo',
  };

  print(countryCapital['India']);  // Output: New Delhi
}

Adding and Updating Values in Map

You can add a new key-value pair or update an existing one like this:


void main() {
  Map<String, String> countryCapital = {
    'India': 'New Delhi',
    'USA': 'Washington DC',
  };

  // Adding
  countryCapital['Japan'] = 'Tokyo';

  // Updating
  countryCapital['USA'] = 'New Washington';

  print(countryCapital);
}

Output:


{India: New Delhi, USA: New Washington, Japan: Tokyo}

Checking if a Key Exists


void main() {
  Map<String, String> countryCapital = {
    'India': 'New Delhi',
    'USA': 'Washington DC',
  };

  print(countryCapital.containsKey('India')); // true
  print(countryCapital.containsKey('France')); // false
}

Iterating Over a Map

Example: Using forEach()


void main() {
  Map<String, String> countryCapital = {
    'India': 'New Delhi',
    'USA': 'Washington DC',
    'Japan': 'Tokyo',
  };

  countryCapital.forEach((key, value) {
    print('Country: $key, Capital: $value');
  });
}

Removing Elements from Map


void main() {
  Map<String, String> countryCapital = {
    'India': 'New Delhi',
    'USA': 'Washington DC',
    'Japan': 'Tokyo',
  };

  countryCapital.remove('USA');

  print(countryCapital);
}

Map Properties and Methods

.length - Number of key-value pairs
.keys - All keys
.values - All values
.isEmpty - Check if empty
.isNotEmpty - Check if not empty

Example:


void main() {
  Map<String, String> countryCapital = {
    'India': 'New Delhi',
    'USA': 'Washington DC',
  };

  print(countryCapital.length);  // 2
  print(countryCapital.keys);    // (India, USA)
  print(countryCapital.values);  // (New Delhi, Washington DC)
  print(countryCapital.isEmpty); // false
}

Maps with Different Data Types

Map with Integer Keys and String Values:


void main() {
  Map<int, String> studentNames = {
    1: 'Rahul',
    2: 'Sneha',
    3: 'Arjun',
  };

  print(studentNames);
}

Using Map in Flutter

Maps are widely used in Flutter for things like sending data between screens, API responses, and storing widget properties.

Example: Passing data using Map


Navigator.pushNamed(
  context,
  '/details',
  arguments: {'id': 101, 'name': 'Product A'},
);

Common Interview Questions on Dart Map

What is a Map in Dart?
How do you iterate through a Map?
Difference between Map and List?
How to convert Map to JSON?

To Do Assignments

Create a Map of Roll Number and Student Names.
Write a Dart program to count word frequency in a given string using Map.
Make a program to check if a value exists inside the Map.
Create a program that removes all keys whose values start with a particular letter.

Conclusion

Maps are super useful when you want to store and retrieve data in key-value form in Dart and Flutter. Understanding how to manipulate Maps makes your Dart coding journey much easier!