Introduction to Flutter & Dart

What is Dart and what are its main features?

Answer:

Dart is a programming language developed by Google, primarily designed for cross-platform application development with Flutter. Its main features include:

  • Object-oriented: based on classes and objects, supports inheritance and polymorphism
  • Null safety: prevents errors caused by uninitialized variables (int? is nullable, int is not)
  • Strong, static typing: every variable has a well-defined type
  • Modern, clean syntax: similar to JavaScript and C#
  • Asynchronous support with Future and Stream

What is the difference between var, final, and const?

Answer:

  • var: declares a variable with inferred type, can be reassigned
  • final: can be assigned only once, but may reference a mutable object
  • const: compile-time constant, immutable and cannot reference non-constant objects
var name = "Manuel";           // can change  
final today = DateTime.now();  // assigned once  
const pi = 3.14;               // pure constant

How do you define a function with optional parameters and default values?

Answer:

String greet({String name = "guest"}) {
  return "Hello, $name!";
}

Parameters inside {} are named and optional.
Default values can be assigned. Dart also supports optional positional parameters: [String name].

What is the difference between classes and mixins?

Answer:

A class is the base structure that can be extended (extends) or implemented (implements).
A mixin allows you to add functionality to a class without using multiple inheritance.

mixin Logger {
  void log(String msg) => print("LOG: $msg");
}

class Service with Logger {
  void run() {
    log("Service executed.");
  }
}

Mixins are ideal for reusing logic without creating complex hierarchies.

What are Future, async/await, and Stream?

Answer:

  • Future represents data that will be available in the future (e.g. an HTTP request)
  • async marks a function as asynchronous
  • await pauses execution until the Future completes
  • Stream represents a sequence of asynchronous events (e.g. timers, user input)
Future<String> greetLater() async {
  await Future.delayed(Duration(seconds: 1));
  return "Hello after one second!";
}

Flutter concepts

What is the difference between StatelessWidget and StatefulWidget?

Answer:

  • StatelessWidget: immutable UI, does not change over time — ideal for static interfaces
  • StatefulWidget: UI that can change state (e.g. counters, user input).
    It has an associated State object that manages dynamic behavior.
class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text("Immutable");
  }
}

class Counter extends StatefulWidget {
  @override
  State<Counter> createState() => _CounterState();
}

class _CounterState extends State<Counter> {
  int value = 0;

  void increment() {
    setState(() {
      value++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text("$value"),
        ElevatedButton(onPressed: increment, child: Text("Increment")),
      ],
    );
  }
}

What is the lifecycle of a StatefulWidget?

Answer:

Main lifecycle phases:

  • createState(): creates the associated state
  • initState(): called once at initialization
  • build(): called every time the state changes
  • dispose(): called when the widget is removed

It is used to manage resources such as controllers and listeners.

How do you navigate between screens?

Answer:

Basic navigation:

Navigator.push(context, MaterialPageRoute(
  builder: (context) => SecondPage()));

To go back:

Navigator.pop(context);

Named routes:

Navigator.pushNamed(context, "/profile");

Routes must be configured in MaterialApp → routes.

How is state managed in Flutter?

Answer:

Flutter offers several approaches:

  • setState() → basic, for simple local state
  • Provider → simple and reactive
  • Riverpod → advanced, Provider-based
  • Bloc → Stream-based pattern, verbose but scalable

Companies often choose Provider or Riverpod for simplicity and testability.

Practical questions

How do you create a dynamic scrollable list?

ListView.builder(
  itemCount: items.length,
  itemBuilder: (context, index) {
    return ListTile(
      title: Text(items[index]),
    );
  },
);

Ideal when the list length is dynamic or large.

How do you display an image from the internet?

Image.network("https://example.com/img.jpg");

You can also use Image.asset() for local images.

How do you add padding and margin?

Answer:

  • Padding: wraps a widget adding internal spacing
  • Container: can have margin, padding, and decoration
Padding(
  padding: EdgeInsets.all(8.0),
  child: Text("Text"),
)
Container(
  margin: EdgeInsets.symmetric(horizontal: 10),
  child: Text("Text with margin"),
)

How do you implement a login screen with validation?

Answer:

Use TextFormField, Form, and GlobalKey<FormState>().
Validate with validator and formKey.currentState!.validate().

final _formKey = GlobalKey<FormState>();
String email = "";

Form(
  key: _formKey,
  child: Column(
    children: [
      TextFormField(
        onChanged: (val) => email = val,
        validator: (val) => val!.contains("@") ? null : "Invalid email",
      ),
      ElevatedButton(
        onPressed: () {
          if (_formKey.currentState!.validate()) {
            print("Valid login!");
          }
        },
        child: Text("Login"),
      ),
    ],
  ),
);

How do you make HTTP requests?

Answer:

Using the http or dio package.

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

Future<void> getData() async {
  final response = await http.get(Uri.parse("https://api.example.com/data"));

  if (response.statusCode == 200) {
    print(response.body);
  } else {
    throw Exception("HTTP error");
  }
}

Use try / catch and handle errors properly.

Package management

What is pubspec.yaml?

Answer:

It is the app configuration file for packages and resources.
It includes:

  • Project name
  • Flutter/Dart versions
  • Dependencies (http, provider, etc.)
  • Assets (images, fonts)
dependencies:
  flutter:
    sdk: flutter
  provider: ^6.0.0
flutter:
  assets:
    - images/

After each change, run flutter pub get.

Related Articles