Dart Cheat Sheet

Dart is a modern, strongly typed programming language optimized for client development, especially for building cross-platform applications. This Dart cheatsheet is an example-driven reference covering core syntax, types, collections, object-oriented features, and asynchronous programming.

Basic Program Structure

void main() {
  print('Hello, Dart');
}

Variables

var a = 10;
int b = 20;
final c = 30;
const d = 40;

var → inferred type
final → set once at runtime
const → compile-time constant

Built-in Types

int x = 10;
double y = 3.14;
bool flag = true;
String text = 'hello';

num n1 = 10;
num n2 = 3.5;

Null Safety

int? value = null;

if (value != null) {
  print(value);
}

int result = value ?? 0;

value ??= 5;

Strings

String s = 'Dart';

s.toUpperCase();
s.contains('a');

String name = 'World';
print('Hello $name');
print('2 + 2 = ${2 + 2}');

Operators

a + b;
a - b;
a * b;
a / b;
a ~/ b;
a % b;

a == b;
a != b;
a > b;
a < b;

a && b;
a || b;
!a;

Control Flow

if / else

if (x > 10) {
  print('large');
} else {
  print('small');
}

switch

switch (x) {
  case 1:
    break;
  case 2:
    break;
  default:
    break;
}

Loops

for (int i = 0; i < 5; i++) {
  print(i);
}

while (x > 0) {
  x--;
}

do {
  x--;
} while (x > 0);

Functions

int add(int a, int b) {
  return a + b;
}

int result = add(2, 3);

Arrow Functions

int square(int x) => x * x;

Optional Parameters

Positional

void log(String message, [String? tag]) {
  print(tag ?? message);
}

Named

void connect({required String host, int port = 80}) {
}

connect(host: 'localhost', port: 8080);

Collections

List

List<int> numbers = [1, 2, 3];
numbers.add(4);
numbers[0];

Set

Set<int> values = {1, 2, 3};
values.add(4);

Map

Map<String, int> scores = {
  'a': 1,
  'b': 2,
};

Collection If / For

var list = [
  1,
  if (x > 2) 3,
  for (var i in [4, 5]) i,
];

Iteration

for (var item in numbers) {
  print(item);
}

numbers.forEach((n) {
  print(n);
});

Classes

class Counter {
  int value = 0;

  void increment() {
    value++;
  }
}

var counter = Counter();
counter.increment();

Constructors

class Point {
  final int x;
  final int y;

  Point(this.x, this.y);
}

var p = Point(10, 20);

Named Constructors

class User {
  String name;

  User(this.name);
  User.guest() : name = 'guest';
}

Getters & Setters

class Box {
  double _value = 0;

  double get value => _value;
  set value(double v) => _value = v;
}

Inheritance

class Animal {
  void speak() {}
}

class Dog extends Animal {
}

Abstract Classes

abstract class Shape {
  double area();
}

class Square extends Shape {
  final double size;
  Square(this.size);

  double area() => size * size;
}

Interfaces (implements)

class Logger {
  void log(String msg) {}
}

class ConsoleLogger implements Logger {
  void log(String msg) {
    print(msg);
  }
}

Mixins

mixin Fly {
  void fly() {}
}

class Bird with Fly {
}

Enums

enum Status { ok, error, loading }

Futures

Future<int> fetchValue() async {
  await Future.delayed(Duration(seconds: 1));
  return 42;
}

int v = await fetchValue();

Async / Await

void main() async {
  var value = await fetchValue();
  print(value);
}

Streams

Stream<int> countStream() async* {
  for (int i = 0; i < 3; i++) {
    yield i;
  }
}

await for (var value in countStream()) {
  print(value);
}

Exception Handling

try {
  int.parse('x');
} catch (e) {
  print(e);
} finally {
}

Typedefs

typedef IntOperation = int Function(int a, int b);

IntOperation sum = (a, b) => a + b;

Generics

class Box<T> {
  T value;
  Box(this.value);
}

var box = Box<int>(10);

File I/O (Dart VM)

import 'dart:io';

File file = File('data.txt');
file.writeAsStringSync('text');
String text = file.readAsStringSync();

JSON

import 'dart:convert';

var data = {'a': 1};
String encoded = jsonEncode(data);
var decoded = jsonDecode(encoded);