Dagger technical analysis and practice
Dagger technical analysis and practice
Dagger is a dependencies in Java and Android applications.It is developed and maintained by Google, which aims to simplify the writing, testing and maintenance of code.This article will analyze Dagger's technical principles in detail and provide some Java code examples to help readers better understand and practice.
1. What is dependent injection?
Dependent injection is a design pattern that is used to manage the dependency relationship between objects.Under normal circumstances, we need to manually instantiate objects and maintain the relationship between them, which will cause the complexity and maintenance of code to decrease.The use of dependency injection can hand over the management of the object's creation and dependency relationship to the framework, thereby reducing the burden of developers and making the code more concise and testable.
Second, the basic principle of dagger
The core principle of Dagger is to achieve dependency injection through code generation.It uses the Annotion Processor function in Java to generate related code during compilation.Developers only need to use some specific annotations in the code to indicate dependency relationships, and Dagger will automatically generate the code for us.
Third, the basic usage of dagger
First of all, we need to add Dagger to the project's built.gradle file: Dagger dependencies:
dependencies {
implementation 'com.google.dagger:dagger:2.x'
annotationProcessor 'com.google.dagger:dagger-compiler:2.x'
}
We can then use some annotations in the code to define dependency relationships.For example, we can use the@inject` annotation to mark a field or constructor that needs to be relying on injection:
public class UserRepository {
private ApiService apiService;
@Inject
public UserRepository(ApiService apiService) {
this.apiService = apiService;
}
}
Next, we need to create a component (Component) to generate dependencies.In the component, we can use the@component` annotation to indicate the dagger generating related code:
@Component
public interface ApplicationComponent {
UserRepository getUserRepository();
}
Finally, we need to initialize the Dagger at the entrance of the application and use the generated component to obtain the dependent object:
public class MyApplication extends Application {
private ApplicationComponent component;
@Override
public void onCreate() {
super.onCreate();
component = DaggerApplicationComponent.builder()
.build();
UserRepository userRepository = component.getUserRepository();
}
}
When we compile applications, Dagger will automatically generate the required code according to the annotations and rules we designated.In the above example, Dagger will generate a `DaggerapplicationComponent` class, and we can obtain the` UserRePOSITORY` object through this class.
Fourth, high -level usage of dagger
In addition to basic dependency injection functions, Dagger also supports some advanced usage, such as scope scope and module.By using the scope of use, we can control the life cycle of the dependent object; while using the module, we can control the fine -grained control of the dependent object.
Below is a simple example that demonstrates how to use the scope and module to control the dependent object:
@UserScope
@Component(modules = {UserModule.class})
public interface UserComponent {
UserRepository getUserRepository();
}
@Scope
@Retention(RetentionPolicy.RUNTIME)
public @interface UserScope {
}
@Module
public class UserModule {
@Provides
@UserScope
public ApiService provideApiService() {
return new ApiService();
}
}
In the above examples, we created a `UserScope" annotation to indicate the scope of the scope of action.Then, in the `usercomponent` component, we used the` UserModule` module, and added the `@Userscope` annotation to mark the scope of the dependent object.
In this way, we can ensure that the dependencies in the same scope are the same instance to better manage their life cycle.
5. Conclusion
This article briefly introduces the technical principles of Dagger and provides some Java code examples to help readers better understand and practice.By using Dagger, we can simplify the writing and testing of the code, and better manage the dependency relationship between objects.It is hoped that readers can master this powerful dependency injection framework through practice to improve development efficiency and code quality.
