Dependency injection (GetIt) in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flutter widget using GetIt?

Consider this Flutter widget that uses GetIt to get a service instance. What will be displayed on the screen?

Flutter

import 'package:flutter/material.dart';
import 'package:get_it/get_it.dart';

class CounterService {
  int count = 0;
  void increment() => count++;
}

final getIt = GetIt.instance;

void setup() {
  getIt.registerSingleton<CounterService>(CounterService());
}

class CounterWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counter = getIt<CounterService>();
    counter.increment();
    return Text('Count: ${counter.count}');
  }
}

void main() {
  setup();
  runApp(MaterialApp(home: Scaffold(body: Center(child: CounterWidget()))));
}

A Count: 1

B Runtime error: Service not found

C Count: 2

D Count: 0

💡 Hint

Think about when the increment() method is called and how many times the widget builds.

The CounterService is registered once as a singleton. When CounterWidget builds, it calls increment() once, so the count becomes 1. The widget then displays 'Count: 1'.

❓ state_output

intermediate

What is the value of count after multiple widget rebuilds?

Given this Flutter app using GetIt singleton service, what will be the value of count after the button is pressed 3 times?

Flutter

import 'package:flutter/material.dart';
import 'package:get_it/get_it.dart';

class CounterService {
  int count = 0;
  void increment() => count++;
}

final getIt = GetIt.instance;

void setup() {
  getIt.registerSingleton<CounterService>(CounterService());
}

class CounterApp extends StatefulWidget {
  @override
  State<CounterApp> createState() => _CounterAppState();
}

class _CounterAppState extends State<CounterApp> {
  final counter = getIt<CounterService>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(child: Text('Count: ${counter.count}')),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            counter.increment();
          });
        },
        child: Icon(Icons.add),
      ),
    );
  }
}

void main() {
  setup();
  runApp(MaterialApp(home: CounterApp()));
}

A Count: 0

B Count: 3

C Count: 1

D Count: 6

💡 Hint

Each button press calls increment() once and triggers a rebuild.

The CounterService is a singleton, so the same instance is used. Each button press increments count by 1. After 3 presses, count is 3.

📝 Syntax

advanced

Which option correctly registers a lazy singleton with GetIt?

Which code snippet correctly registers a lazy singleton service with GetIt so that the instance is created only when first used?

A getIt.registerFactory(() => MyService());

B getIt.registerSingleton(() => MyService());

C getIt.registerLazySingleton(MyService());

D getIt.registerLazySingleton(() => MyService());

💡 Hint

Lazy singleton means the instance is created only when requested first time.

Option D uses registerLazySingleton with a factory function, which creates the instance lazily. Option D registers an immediate singleton, A registers a factory (new instance every time), and D is invalid because it passes an instance instead of a factory.

🔧 Debug

advanced

Why does this GetIt code throw an error at runtime?

Given this code snippet, why does it throw a GetItNotFoundException when trying to get the service?

Flutter

final getIt = GetIt.instance;

class ApiService {}

void main() {
  // Missing registration
  final api = getIt<ApiService>();
}

A The ApiService was never registered with GetIt before retrieval.

B The ApiService class is abstract and cannot be instantiated.

C GetIt requires async initialization before use.

D The GetIt instance was not created with GetIt.instance.

💡 Hint

Check if the service was registered before calling getIt().

GetIt throws GetItNotFoundException if you try to get a service that was never registered. Here, ApiService was not registered before retrieval.

🧠 Conceptual

expert

What is the main benefit of using GetIt for dependency injection in Flutter?

Choose the best explanation for why developers use GetIt for dependency injection in Flutter apps.

A It replaces Flutter's widget tree with a service-oriented architecture.

B It automatically generates UI code based on service definitions.

C It allows decoupling of object creation from usage, making testing and maintenance easier.

D It enforces strict compile-time type checking for all dependencies.

💡 Hint

Think about how dependency injection helps with code structure and testing.

GetIt helps separate how objects are created from where they are used. This decoupling makes it easier to swap implementations, write tests, and maintain code. It does not generate UI code, replace widget trees, or enforce compile-time checks beyond Dart's normal typing.