The Ultimate Guide to GetIt Package in Flutter: Everything You Need to Know

Ever felt like your Flutter app’s code could use a little less chaos and a lot more order? Enter GetIt, the unsung hero of dependency injection! This nifty package turns your app into a well-oiled machine by acting as a central hub for all your services, making dependency management smoother than ever.

Forget the tangled mess of repeated instances and clunky code—GetIt brings simplicity to the table. Whether you're tired of juggling InheritedWidget or wrestling with Provider, this service locator has your back. With GetIt, you can access the same instance of a class across your app effortlessly, freeing you up to focus on what truly matters: building incredible Flutter experiences.

Setting Up get_it

To use get_it, add it to your yaml file and set up a get_it instance. This can be done in the main function of your Dart file. The setup function for get_it is typically written in a Dart file separate from the main function.

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final getIt = GetIt.instance;

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

In the above example, we have created a new instance of the AppModel class and registered it with get_it. We can now access this instance from anywhere in our Flutter app.

Accessing Services with get_it

Once you have registered a service with get_it, you can access it using the buildcontext context in your Flutter widgets. This allows your UI code to access the services it needs without directly depending on them.

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MaterialButton(
  child: Text("Update"),
  onPressed: getIt<AppModel>().update
),

In the above example, we are accessing the update method of the AppModel class that we registered with get_it earlier.

Implementing Dependency Injection with get_it

To implement dependency injection with get_it, you can use it for both setter injection and constructor injection. This reduces the amount of boilerplate code you need to write in your Flutter app, making it easier to manage dependencies.

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class Example {
  Service service;

  Example() {
    service = getIt<Service>();
  }
}

In the above example, we are using constructor injection to inject an instance of the Service class into the Example class. This instance is retrieved from the get_it service locator.

Working with Async Functions in get_it

Get_it also supports working with async functions. Register a service with an async function in get_it and then access it in your Flutter application.

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void setup() {
  getIt.registerSingletonAsync<Service>(() async => await Service.create());
}

In the above example, we register a service with an async function that returns a Future of the Service class. This allows us to perform asynchronous operations when creating the service.

Setting Up get_it in a Flutter Project

Setting up get_it in a Flutter project involves adding the get_it package to your project's yaml file and then initializing a get_it instance in your project's main function.

Adding get_it to the yaml file

To start using get_it in your Flutter project, add it to your project's yaml file. This file is where you list all the dependencies for your project.

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dependencies:
  flutter:
    sdk: flutter
  get_it: ^7.2.0

In the above example, we have added get_it as a dependency to our Flutter project. Before the version number, the caret (^) means that the project can use any version of get_it that is compatible with version 7.2.0.

Setting up the get_it instance

After adding get_it to your yaml file, the next step is to set up a get_it instance. This is typically done in the main function of your Dart file. You can create a setup function for get_it and call this function in your main function.

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final getIt = GetIt.instance;

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

void main() {
  setup();
  runApp(MyApp());
}

In the above example, we have created a setup function that registers an instance of the AppModel class with get_it. We then call this setup function in our main function.

Accessing the get_it instance

Once you have set up the get_it instance, you can access it anywhere in your Flutter app using the get_it global variable.

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class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final appModel = getIt<AppModel>();
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text(appModel.title),
        ),
      ),
    );
  }
}

In the above example, we are accessing the get_it instance in a Flutter widget to get an instance of the AppModel class. We then use this instance to set the title of the app bar in our app.

Registering Services with get_it

The get_it package allows you to register services and access them anywhere in your Flutter app. This can be done using various methods, such as registering a simple service locator for an abstract class, registering a new instance or the same instance with get_it, and exploring different registration types.

Registering a Simple Service Locator

To register a simple service locator for an abstract class, you can use the registerSingleton or registerLazySingleton methods provided by get_it.

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abstract class Service {}

class ServiceImpl extends Service {}

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

In the above example, we have defined an abstract Service class and a ServiceImpl class that extends Service. We then register ServiceImpl as a singleton instance of Service using the registerSingleton method.

Registering a New Instance and the Same Instance

With get_it, you can register a new or the same class instance. Registering a new instance means that every time you call get_it<Service>(), you will get a new instance of Service. Registering the same instance means you will get the same service instance every time you call get_it<Service>().

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void setup() {
  getIt.registerFactory<Service>(() => ServiceImpl()); // New instance
  getIt.registerSingleton<Service>(ServiceImpl()); // Same instance
}

In the above example, we register ServiceImpl as a factory, meaning a new instance will be created every time we call get_it<Service>(). We also register ServiceImpl as a singleton, meaning the same instance will be returned whenever we call get_it<Service>().

Exploring Different Registration Types

Get_it offers different registration types such as lazy singletons, factory functions, and constructor injection. A lazy singleton is a singleton that is only created when it is first requested. A factory function is a function that returns a new instance of a class. Constructor injection is a form of dependency injection where dependencies are provided through a class constructor.

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void setup() {
  getIt.registerLazySingleton<Service>(() => ServiceImpl()); // Lazy singleton
  getIt.registerFactory<Service>(() => ServiceImpl()); // Factory function
}

In the above example, we register ServiceImpl as a lazy singleton and a factory function.

Implementing Dependency Injection with get_it

Dependency injection is a software design pattern that allows us to develop loosely coupled code. It is a form of inversion of control; this means that the custom-written portions of a computer program receive the flow of control from a generic, reusable library. To implement dependency injection in Dart and Flutter, we can use the get_it package.

Using get_it for Setter Injection and Constructor Injection

Get_it can be used for both setter injection and constructor injection. Setter injection is a type of dependency injection where the dependencies are provided through setter methods. In contrast, constructor injection is a type of dependency injection where the dependencies are provided through a class constructor.

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class Service {}

class Example {
  late Service _service;

  // Setter injection
  set service(Service service) {
    _service = service;
  }

  // Constructor injection
  Example(this._service);
}

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

In the above example, we have an Example class that has a dependency on a Service class. We provide this dependency using both setter injection and constructor injection.

Reducing Boilerplate Code with get_it

One of the advantages of using get_it is that it can reduce boilerplate code in your Flutter app. By registering your services with get_it, you can access them from anywhere in your app without having to instantiate them manually every time.

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void main() {
  setup();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final example = getIt<Example>();
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Example App'),
        ),
        body: Center(
          child: Text('Service: ${example.service}'),
        ),
      ),
    );
  }
}

In the above example, we access the Example service from our app's UI code using get_it. This means we don't have to manually instantiate Example whenever we want to use it.

Working with Async Functions in get_it

The get_it package supports working with async functions. This allows you to perform asynchronous operations when registering and accessing services in your Flutter app.

Registering a Service with an Async Function

You can register a service with an async function in get_it. Creating the service allows you to perform asynchronous operations, such as fetching data from a database or a network request.

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Future<Service> createService() async {
  // Perform async operations
  return Service();
}

void setup() {
  getIt.registerSingletonAsync<Service>(createService);
}

In the above example, we have an async function createService that returns a Future of Service. We then register this function with get_it using the registerSingletonAsync method.

Accessing a Service Registered with an Async Function

Once you have registered a service with an async function, you can access it in your Flutter app using the getAsync method provided by get_it. This method returns a Future of the service, which you can await to get the actual service.

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class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder<Service>(
      future: getIt.getAsync<Service>(),
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.done) {
          final service = snapshot.data;
          // Use the service
          return MaterialApp(/* ... */);
        } else {
          return CircularProgressIndicator();
        }
      },
    );
  }
}

In the above example, we use a FutureBuilder to await the Future returned by get_it.getAsync<Service>(). Once the Future completes, we can use the service in our app.

Wrapping It Up: Dependency Magic with GetIt

The GetIt package isn’t just a tool; it’s your backstage pass to building smarter, cleaner Flutter apps! With its service locator wizardry, you can effortlessly manage dependencies, dodge repetitive code, and keep things sleek across your app.

Whether you’re injecting dependencies with a constructor, setting them up with a setter, or juggling async services, GetIt is like your coding sidekick—always ready to keep things tidy and efficient. And let’s not forget the joy of fewer headaches when debugging! 😄 So, the next time you dive into Flutter, think of GetIt as the superhero cape your code didn’t know it needed. Your app’s performance will thank you, and your future self will, too!