List Mastery — Methods & Operations

A List in Dart is an ordered collection of items. It is one of the most commonly used data structures, equivalent to arrays in other languages — but far more powerful.

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1. Creating Lists

Literal Syntax — []

dart
void main() {
  // Typed list
  List<int> numbers = [1, 2, 3, 4, 5];
  List<String> names = ['Amit', 'Priya', 'Rahul'];
  List<bool> flags = [true, false, true];

  // Type inferred by Dart
  var colors = ['red', 'green', 'blue']; // List<String>

  // Empty list
  List<double> prices = [];
  var items = <String>[];
}

List.filled() — Fixed Size with Default Value

Creates a list of a specific size, with every element set to a default value.

dart
void main() {
  // 5 zeros
  var zeros = List.filled(5, 0);
  print(zeros); // [0, 0, 0, 0, 0]

  // 3 empty strings
  var blanks = List.filled(3, '');
  print(blanks); // ['', '', '']
}

List.generate() — Generate Elements Programmatically

dart
void main() {
  // Generate squares: [0, 1, 4, 9, 16]
  var squares = List.generate(5, (i) => i * i);
  print(squares); // [0, 1, 4, 9, 16]

  // Generate a list of labels
  var labels = List.generate(4, (i) => 'Item ${i + 1}');
  print(labels); // [Item 1, Item 2, Item 3, Item 4]

  // Generate even numbers
  var evens = List.generate(5, (i) => i * 2);
  print(evens); // [0, 2, 4, 6, 8]
}

Growable vs Fixed-Length Lists

dart
void main() {
  // Growable (default) — you can add/remove elements
  var growable = [1, 2, 3];
  growable.add(4); // OK

  // Fixed-length — size cannot change
  var fixed = List.filled(3, 0, growable: false);
  // fixed.add(4); // ERROR: Cannot add to a fixed-length list

  // Fixed lists still allow value changes
  fixed[0] = 99;
  print(fixed); // [99, 0, 0]
}

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2. Accessing Elements

dart
void main() {
  List<String> fruits = ['mango', 'apple', 'banana', 'grape', 'orange'];

  // By index (0-based)
  print(fruits[0]);          // mango
  print(fruits[2]);          // banana

  // .first and .last
  print(fruits.first);       // mango
  print(fruits.last);        // orange

  // .elementAt() — same as [] but method syntax
  print(fruits.elementAt(3)); // grape

  // .length
  print(fruits.length);      // 5

  // Check if empty
  print(fruits.isEmpty);     // false
  print(fruits.isNotEmpty);  // true
}

---

3. Adding Elements

dart
void main() {
  List<String> cart = ['Laptop'];

  // add() — single element at the end
  cart.add('Mouse');
  print(cart); // [Laptop, Mouse]

  // addAll() — multiple elements at the end
  cart.addAll(['Keyboard', 'Monitor']);
  print(cart); // [Laptop, Mouse, Keyboard, Monitor]

  // insert() — at specific index
  cart.insert(1, 'Mousepad');
  print(cart); // [Laptop, Mousepad, Mouse, Keyboard, Monitor]

  // insertAll() — multiple at specific index
  cart.insertAll(0, ['USB Hub', 'Webcam']);
  print(cart); // [USB Hub, Webcam, Laptop, Mousepad, Mouse, Keyboard, Monitor]
}

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4. Removing Elements

dart
void main() {
  List<int> numbers = [1, 2, 3, 4, 5, 2, 6];

  // remove() — removes FIRST occurrence of the value
  numbers.remove(2);
  print(numbers); // [1, 3, 4, 5, 2, 6]

  // removeAt() — removes at specific index
  numbers.removeAt(0);
  print(numbers); // [3, 4, 5, 2, 6]

  // removeLast() — removes the last element
  numbers.removeLast();
  print(numbers); // [3, 4, 5, 2]

  // removeWhere() — removes all elements matching a condition
  numbers.removeWhere((n) => n % 2 == 0);
  print(numbers); // [3, 5]

  // clear() — removes all elements
  numbers.clear();
  print(numbers); // []
}

---

5. Searching & Checking

dart
void main() {
  List<String> cities = ['Mumbai', 'Delhi', 'Pune', 'Bangalore', 'Pune'];

  // contains() — true/false
  print(cities.contains('Pune'));      // true
  print(cities.contains('Chennai'));   // false

  // indexOf() — first occurrence index (-1 if not found)
  print(cities.indexOf('Pune'));       // 2
  print(cities.indexOf('Chennai'));    // -1

  // lastIndexOf() — last occurrence
  print(cities.lastIndexOf('Pune'));   // 4

  // indexWhere() — find index by condition
  int idx = cities.indexWhere((city) => city.startsWith('B'));
  print(idx); // 3 (Bangalore)

  // any / every (HOF-style)
  print(cities.any((c) => c.length > 8));    // true (Bangalore)
  print(cities.every((c) => c.length > 3));  // true
}

---

6. Sorting

dart
void main() {
  List<int> scores = [78, 45, 92, 61, 88];

  // Default sort (ascending)
  scores.sort();
  print(scores); // [45, 61, 78, 88, 92]

  // Custom sort — descending
  scores.sort((a, b) => b.compareTo(a));
  print(scores); // [92, 88, 78, 61, 45]

  List<String> names = ['Zara', 'Amit', 'Priya', 'Karan'];

  // Alphabetical
  names.sort((a, b) => a.compareTo(b));
  print(names); // [Amit, Karan, Priya, Zara]

  // By length
  names.sort((a, b) => a.length.compareTo(b.length));
  print(names); // [Amit, Zara, Karan, Priya]
}

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7. Slicing with sublist()

dart
void main() {
  List<int> numbers = [10, 20, 30, 40, 50, 60, 70];

  // sublist(start) — from index to end
  print(numbers.sublist(3));    // [40, 50, 60, 70]

  // sublist(start, end) — start inclusive, end exclusive
  print(numbers.sublist(1, 4)); // [20, 30, 40]

  // Get first 3 elements
  print(numbers.sublist(0, 3)); // [10, 20, 30]

  // Get last 3 elements
  print(numbers.sublist(numbers.length - 3)); // [50, 60, 70]
}

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8. Spread Operator with Lists

The ... spread operator lets you expand a list into another:

dart
void main() {
  List<int> list1 = [1, 2, 3];
  List<int> list2 = [4, 5, 6];

  // Combine lists
  List<int> combined = [...list1, ...list2];
  print(combined); // [1, 2, 3, 4, 5, 6]

  // Insert in the middle
  List<int> withMiddle = [...list1, 99, 100, ...list2];
  print(withMiddle); // [1, 2, 3, 99, 100, 4, 5, 6]

  // Null-aware spread (...?)
  List<int>? maybeNull;
  List<int> safe = [...list1, ...?maybeNull];
  print(safe); // [1, 2, 3]

  // Copy a list (avoids reference sharing)
  List<int> copy = [...list1];
  copy.add(4);
  print(list1); // [1, 2, 3] — unchanged
  print(copy);  // [1, 2, 3, 4]
}

---

9. List of Lists — 2D Lists

dart
void main() {
  // 2D list (matrix)
  List<List<int>> matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
  ];

  // Access element at row 1, col 2
  print(matrix[1][2]); // 6

  // Print all rows
  for (var row in matrix) {
    print(row);
  }
  // [1, 2, 3]
  // [4, 5, 6]
  // [7, 8, 9]

  // Generate a 3x3 zero matrix
  var zeroMatrix = List.generate(3, (_) => List.filled(3, 0));
  print(zeroMatrix); // [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
}

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10. Type Annotations

dart
void main() {
  // Explicit type annotations
  List<int> integers = [1, 2, 3];
  List<String> strings = ['a', 'b', 'c'];
  List<double> doubles = [1.1, 2.2, 3.3];
  List<bool> booleans = [true, false, true];

  // List of objects (mixed — avoid in practice)
  List<dynamic> mixed = [1, 'hello', true, 3.14];

  // Using var (type inferred)
  var inferredList = [10, 20, 30]; // Dart infers List<int>
}

---

11. Real Project — Todo List Manager

dart
class Todo {
  final String id;
  String title;
  bool isCompleted;

  Todo(this.id, this.title, {this.isCompleted = false});

  @override
  String toString() => '[${ isCompleted ? "✓" : " " }] $title';
}

class TodoList {
  final List<Todo> _todos = [];

  // Add a new todo
  void add(String title) {
    _todos.add(Todo(DateTime.now().toString(), title));
    print('Added: "$title"');
  }

  // Mark a todo complete by index
  void complete(int index) {
    if (index >= 0 && index < _todos.length) {
      _todos[index].isCompleted = true;
    }
  }

  // Remove a todo by index
  void remove(int index) {
    if (index >= 0 && index < _todos.length) {
      String removed = _todos[index].title;
      _todos.removeAt(index);
      print('Removed: "$removed"');
    }
  }

  // Clear completed todos
  void clearCompleted() {
    _todos.removeWhere((todo) => todo.isCompleted);
    print('Cleared completed todos.');
  }

  // Get remaining count
  int get remaining => _todos.where((t) => !t.isCompleted).length;

  // Print all todos
  void printAll() {
    print('\n--- Todo List (${_todos.length} items, $remaining remaining) ---');
    for (int i = 0; i < _todos.length; i++) {
      print('  $i. ${_todos[i]}');
    }
    print('---');
  }
}

void main() {
  var todoList = TodoList();

  todoList.add('Buy groceries');
  todoList.add('Study Dart collections');
  todoList.add('Exercise for 30 minutes');
  todoList.add('Read a chapter of a book');

  todoList.printAll();

  todoList.complete(0);
  todoList.complete(2);

  todoList.printAll();

  todoList.clearCompleted();
  todoList.printAll();
}

Output:

Added: "Buy groceries"
Added: "Study Dart collections"
Added: "Exercise for 30 minutes"
Added: "Read a chapter of a book"

--- Todo List (4 items, 4 remaining) ---
  0. [ ] Buy groceries
  1. [ ] Study Dart collections
  2. [ ] Exercise for 30 minutes
  3. [ ] Read a chapter of a book
---

--- Todo List (4 items, 2 remaining) ---
  0. [✓] Buy groceries
  1. [ ] Study Dart collections
  2. [✓] Exercise for 30 minutes
  3. [ ] Read a chapter of a book
---
Cleared completed todos.

--- Todo List (2 items, 2 remaining) ---
  0. [ ] Study Dart collections
  1. [ ] Read a chapter of a book
---

---

Summary

Operation	Method(s)
Create	[], List.filled(), List.generate()
Access	[index], .first, .last, .elementAt()
Add	add(), addAll(), insert(), insertAll()
Remove	remove(), removeAt(), removeWhere(), clear()
Search	contains(), indexOf(), indexWhere()
Sort	sort(), sort((a,b) => ...)
Slice	sublist(start, end)
Combine	Spread [...list1, ...list2]
2D	List<List<T>>

Lists are the foundation of data management in Dart and Flutter. Every time you build a list of widgets, manage state, or process API responses — you will be using these operations.