Hilt Inject field into any class with no scope

Hilt Inject Field into Any Class with No Scope

Introduction

Hilt is a popular dependency injection framework for Android that simplifies the process of managing dependencies in your application. While Hilt typically requires you to define the scope of your injected fields, there are scenarios where you might want to inject a field into a class that doesn’t adhere to a specific scope. This article explores how to inject a field into any class without specifying a scope.

The Problem

Hilt generally enforces scope annotations like `@Singleton`, `@ActivityScoped`, or `@ViewModelScoped` to ensure proper lifecycle management and prevent unexpected behavior. However, there are instances where you may have a class that doesn’t naturally fall under a specific scope, such as a utility class or a service that operates independently of the application’s lifecycle.

Solution: NoScope

To inject fields into classes without a defined scope, you can leverage Hilt’s `@NoScope` annotation. The `@NoScope` annotation indicates that the component should not have a specific scope.

Example

1. Define the Class

“`java
public class MyService {
@Inject
public MyService() {
}

public void performAction() {
// …
}
}
“`

2. Inject into a Class without a Scope

“`java
@NoScope
@Component
public interface MyComponent {
MyService myService();
}
“`

3. Use the Injected Field

“`java
public class MyUtilClass {
private MyService myService;

@Inject
public MyUtilClass(MyService myService) {
this.myService = myService;
}

public void useService() {
myService.performAction();
}
}
“`

Caveats

While using `@NoScope` allows you to inject fields without a scope, it’s essential to consider the following:

– **Lifecycle Management**: Without a defined scope, injected objects will be managed at the component level. This means they’ll be created and destroyed with the component’s lifecycle, which may not align with the expected behavior of your class.
– **Singletons**: Be mindful of singleton behavior when using `@NoScope`. If your component is not a singleton, multiple instances of the injected field may be created.

Table: Scope vs. NoScope

Conclusion

Hilt’s `@NoScope` annotation provides flexibility for injecting fields into classes that don’t adhere to a specific scope. However, it’s crucial to understand the implications of using `@NoScope`, particularly in terms of lifecycle management and instance creation. Carefully consider the appropriate scope for your classes to ensure predictable and manageable behavior.