Intro to Dart

To get started with Flutter, you need to have some familiarity with the Dart programming language, which Flutter applications are written in. This page is a gentle introduction to Dart, and if you're comfortable reading the code examples, feel free to skip this page. You do not need to be an expert in Dart to continue with this series.

Flutter applications are built in Dart, a language that will look familiar to anyone who's written Java, Javascript, or any other C-like language.

The following example is a small program that fetches data from dart.dev, decodes the returned json, and prints it to the console. If you're confident in your ability to understand this program, feel free to skip to the page.

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

class Package {
  final String name;
  final String latestVersion; 
  final String? description;

  Package(this.name, this.latestVersion, this.description);

  @override
  String toString() {
    return 'Package{name: $name, latestVersion: $latestVersion, description: $description}';
  }
}

void main() async {
  final httpPackageUrl = Uri.https('dart.dev', '/f/packages/http.json');
  final httpPackageResponse = await http.get(httpPackageUrl);
  if (httpPackageResponse.statusCode != 200) {
    print('Failed to retrieve the http package!');
    return;
  }
  final json = jsonDecode(httpPackageResponse.body);
  final package = Package(json['name'], json['latestVersion'], json['description']);
  print(package);
}

This program has two parts: the Package class declaration, and the business logic, which is contained in the main function.

The Package class contains many of the most common features you'll use when working with classes in Dart. This class has three members, and defines a constructor and a method.

The Dart language is type safe; it uses static type checking to ensure that a variable's value always matches the variable's static type. When defining a class, annotating the members with String is required, but it is often optional due to type inference. In the main function in this example there are many lines that start with final variableName =. These lines are type safe, despite not being explicitly given a type.

Dart also has built-in sound null safety. In the example, the description member is declared with the type String?. The ? at the end of String? means that this property can be null. The other two members cannot be null, and the program will not compile if you tried to set them to null. You can see this demonstrated in the constructor for the Package class. It takes two required, positional arguments and one optional, named argument.

Next in the example is the main function. All Dart programs, including Flutter apps, start with a main function. The function showcases several basic Dart language features, including using libraries, marking functions as async, making function calls, using if statement control-flow, and more.

If these features aren't familiar to you, you can find resources to learn Dart on the Bootstrap into Dart page.

This page is an introduction to Dart, and helps you become familiar with reading Flutter and Dart code. It's okay if you don't feel clear on all the code on this page, as long as you feel comfortable with the syntax of the Dart language. In the next section, you'll learn about the building block of Flutter apps: widgets.

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