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, supporting inheritance and polymorphism
• Null safety: prevents errors from uninitialized variables (int? is nullable, int is not)
• Strong and static typing: every variable has a well-defined type
• Clean and modern syntax: similar to JavaScript and C#
• Asynchronous support with Future and Stream

---

What’s 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 its value may be a mutable object
• const: compile-time constant, immutable and cannot reference non-constant objects

var name = "Manuel";          // can change
final today = DateTime.now(); // one assignment only
const pi = 3.14;              // pure constant

---

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

Answer:

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

Parameters inside {} are named and optional.
You can assign default values. Dart also supports optional positional parameters: [String name].

---

What’s the difference between classes and mixins?

Answer:

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

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

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

Mixins are great for reusing logic without complex hierarchies.

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What are Future, async/await, and Stream?

Answer:

• Future represents data that will be available in the future (e.g. HTTP call)
• async makes a function asynchronous
• await pauses execution until the Future completes
• Stream represents a sequence of async events (e.g. timers, user input)

Future<String> greetLater() async {
  await Future.delayed(Duration(seconds: 1));
  return "Hello after a second!";
}

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Flutter Concepts

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What’s the difference between StatelessWidget and StatefulWidget?

Answer:

• StatelessWidget: immutable UI, doesn’t change over time — ideal for static UI
• StatefulWidget: UI that can change state (e.g. counter, input).
  Has an associated State object that handles 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")),
      ],
    );
  }
}

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What is the lifecycle of a StatefulWidget?

Answer:

Key lifecycle stages:

• createState(): creates associated state
• initState(): called once at start
• build(): called whenever state changes
• dispose(): called when widget is removed

Used to manage resources (e.g. controllers, listeners)

---

How do you navigate between screens?

Answer:

Basic navigation:

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

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 various approaches:

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

Companies often use Provider or Riverpod for simplicity and testability.

---

Practical Questions

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How do you create a dynamic scrollable list?

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

Ideal when list length is dynamic or large.

---

How do you display an image from the network?

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 and adds internal space
• 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("Login valid!");
          }
        },
        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.

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Package Management

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What is pubspec.yaml?

Answer:

It’s the app’s configuration file for packages and resources.
Includes:

• Project name
• Flutter/Dart versions
• Dependencies (http, provider, etc.)
• Assets (images, fonts)

yaml dependencies: flutter: sdk: flutter provider: ^6.0.0 flutter: assets: - images/

After modifying it, run flutter pub get