Dart Cheatsheet

Dart is a programming language optimized for frontend applications such as web and mobile interfaces, focusing on rapid development and runtime performance.

It is widely used with Flutter to create cross-platform mobile applications.

Installation and Setup

Installation on Windows

Download the installer from dart.dev

Installation on Linux

sudo apt update -y
sudo apt install dart

Installation on macOS

brew tap dart-lang/dart
brew install dart

Verify Installation

To check that Dart is correctly installed

dart --version

Compile and run a Dart file

To compile and run a .dart file:

dart run file.dart

Basic Structure

Simple Program

The following code shows a basic program in Dart with the main function as the entry point.

void main() {
  print('Hello, World!');
}

Line Comment

// This is a single-line comment

Block Comment

/*
This is a comment
over multiple lines
*/

Data Types

Primitive Types in Dart

Dart has several primitive data types: int, double, bool, String, and var.

int integer = 42;
double decimal = 3.14;
bool isTrue = true;
String text = 'Hello';
var undefined = 'can be any type';

Constants

In Dart, constants can be defined with const or final.

• const: Value of the constant at compile time.
• final: Fixed value at runtime, but cannot be changed after initialization.

const double pi = 3.1416;
final DateTime now = DateTime.now();

Null Safety

Dart has null safety to avoid null reference errors:

int? age; // Can be null
age = 20;
print(age);

Operators

Dart includes several types of operators to perform operations with variables and constants.

Arithmetic Operators

• + Addition
• - Subtraction
• * Multiplication
• / Division (returns a double)
• ~/ Integer division (returns an int)
• % Modulo (remainder of the division)

int a = 10;
int b = 3;
print(a + b);   // 13
print(a ~/ b);  // 3
print(a % b);   // 1

Assignment Operators

• = Assignment
• +=, -=, *=, /=, ~/=, %=

int c = 5;
c += 2;  // c = 7

Relational Operators

• == Equal to
• != Not equal to
• > Greater than
• < Less than
• >= Greater than or equal to
• <= Less than or equal to

print(5 > 3);   // true

Logical Operators

• && Logical AND
• || Logical OR
• ! Logical NOT

bool isGreater = (5 > 3) && (2 < 4);  // true

Increment/Decrement Operator

• ++ Increment by 1
• -- Decrement by 1

int d = 5;
d++;  // d = 6

Null-aware Operator

• ?? Returns the left value if it is not null, otherwise returns the right value.

String? name;
print(name ?? 'No name');  // 'No name'

Control Flow

Conditionals

if (condition) {
  // code if the condition is true
} else if (otherCondition) {
  // code if the other condition is true
} else {
  // code if no condition is true
}

Ternary Operator

var result = (condition) ? value1 : value2;

Switch-case

switch (variable) {
  case value1:
    // code for value1
    break;
  case value2:
    // code for value2
    break;
  default:
    // code if there are no matches
}

Loops

For Loop

for (int i = 0; i < 10; i++) {
  print(i);
}

While Loop

int i = 0;
while (i < 10) {
  print(i);
  i++;
}

Do-while Loop

int i = 0;
do {
  print(i);
  i++;
} while (i < 10);

Functions

Basic Function Definition

void printMessage(String message) {
  print(message);
}

Function with Return Value

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

Anonymous Functions

var anonymousFunction = () {
  print('This is an anonymous function');
};

Optional Parameters

In Dart, parameters can be optional or have default values:

• Named Parameters:

void greeting({String name = 'friend'}) {
  print('Hello, $name');
}

• Positional Parameters:

void showData(String name, [int age = 0]) {
  print('Name: $name, Age: $age');
}

Arrow Functions

Short functions can be expressed with arrows:

int multiply(int a, int b) => a * b;

Functions as Parameters

void executeFunction(void Function() function) {
  function();
}

void main() {
  executeFunction(() => print('Function executed'));
}

Closures

Function add(int a) {
  return (int b) => a + b;
}

void main() {
  var addWith5 = add(5);
  print(addWith5(3)); // 8
}

Collections

Lists

List Declaration

List<int> numbers = [1, 2, 3, 4, 5];

Accessing Elements

print(list[0]); // Prints 1

Common List Operations

numbers.add(6);
numbers.remove(3);
print(numbers.length);

Sets

Set Declaration

Set<String> names = {'Ana', 'Luis', 'Carlos'};

Set Operations

names.add('Pedro');
names.remove('Ana');

Maps

Map Declaration

Map<String, int> ages = {'Juan': 25, 'Ana': 30};

Accessing Values

print(ages['Juan']); // 25

Classes and Objects

Class Definition

class Person {
  String name;
  int age;

  Person(this.name, this.age);

  void showData() {
    print('Name: $name, Age: $age');
  }
}

Creating an Instance of a Class

void main() {
  var person = Person('Juan', 25);
  person.showData();
}

Using Getters and Setters

class Circle {
  double radius;

  Circle(this.radius);

  double get area => 3.1416 * radius * radius;
  set changeRadius(double newRadius) => radius = newRadius;
}

Named Constructors

class Person {
  String name;
  int age;

  Person(this.name, this.age);
  
  Person.withoutAge(this.name) {
    age = 0;
  }
}

Inheritance

class Animal {
  void sound() {
    print('The animal makes a sound');
  }
}

class Dog extends Animal {
  @override
  void sound() {
    print('The dog barks');
  }
}

Static Methods

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

void main() {
  print(Math.add(5, 3));
}

Asynchronous

Asynchronous Functions

Dart allows executing code asynchronously using Future and async/await.

Future<String> fetchData() async {
  return 'Data fetched';
}

void main() async {
  String result = await fetchData();
  print(result);
}

Simulating Delays

Future<void> simulateDelay() async {
  await Future.delayed(Duration(seconds: 2));
  print('Delay completed');
}

Streams

Using Streams to Handle Data Flows

Stream<int> count() async* {
  for (int i = 1; i <= 5; i++) {
    yield i;
    await Future.delayed(Duration(seconds: 1));
  }
}

void main() async {
  await for (var value in count()) {
    print(value);
  }
}

Error Handling

Try-catch-finally

void main() {
  try {
    int result = 100 ~/ 0; // Division by zero
  } catch (e) {
    print('Error: $e');
  } finally {
    print('Operation completed');
  }
}

Throwing Exceptions

void validateAge(int age) {
  if (age < 18) {
    throw Exception('Invalid age');
  }
}

Packages and Dependency Management

Importing a Library

import 'dart:math';

Creating a New Project

dart create my_project

Managing Dependencies with pubspec.yaml

In this file, you manage your project’s dependencies:

dependencies:
  http: ^0.13.3

To install the dependencies:

dart pub get

Using a Package

import 'package:http/http.dart' as http;

void main() async {
  var response = await http.get(Uri.parse('https://example.com'));
  print(response.body);
}