Master the core principles of the technical core principles of the Dagger framework in the Java library
Master the core principles of the technical core principles of the Dagger framework in the Java library
Brief introduction
Dagger is a Java class library to achieve a framework that depends on dependencies injection.Dependent injection is a design mode to reduce the coupling between modules and improve the testability and maintenance of code.The Dagger framework uses automatic generating code to achieve dependency injection, so that developers can focus on the writing of business logic.
In this article, we will explore the core principles of the Dagger framework and how to use the framework in the Java class library.
1. Dependent injection
Dependent injection is the core concept of the Dagger framework.It allows us to declare and inject dependencies by using annotations without manually writing a large number of initialization code.
In Dagger, we use the@inject` annotation to mark the dependent items that need to be injected.For example, we can use the `@inject` annotation of the constructor, field or method of the class to tell Dagger to inject the dependent item.
public class Foo {
@Inject
Bar bar;
public Foo() {
// Use Dagger into the instance of BAR
DaggerAppComponent.create().inject(this);
}
public void doSomething() {
// Use the injected BAR instance to perform operation
bar.doSomething();
}
}
2. Component (component)
In Dagger, components are the core of injecting.Components are bridges between the modules that are injected and dependent.
We can use the@component` annotation to define a component and use the@module` annotation to define the module required by the component.
@Component(modules = {AppModule.class})
public interface AppComponent {
void inject(Foo foo);
}
@Module
public class AppModule {
@Provides
Bar provideBar() {
return new Bar();
}
}
In the above examples, the `AppComponent` is a component, which depends on the` appmodule` module.`Appmodule` module provides an instance of` bar`.
3. Dependent injection based on annotations
Dagger also supports injection -based dependencies.We can use the note to mark different dependencies to mark different dependencies so that Dagger can distinguish them.
public class Foo {
@Inject
@Database
DataSource database;
@Inject
@Network
DataSource network;
// ...
}
@Qualifier
@Retention(RetentionPolicy.RUNTIME)
public @interface Database {
}
@Qualifier
@Retention(RetentionPolicy.RUNTIME)
public @interface Network {
}
In the above example, there are two different `datasource` dependencies in the` FOO` class, which are marked by `@database` and@network`.
4. Life cycle management
Dagger supports life cycle management of dependencies.We can use `@我们 我们 我们 to mark a dependency item, indicating that it should be a single case.
@Singleton
@Component(modules = {AppModule.class})
public interface AppComponent {
void inject(Foo foo);
}
@Singleton
public class Bar {
// ...
}
In the above example, the `bar` dependency item is marked as`@在, indicating that it should be unique in the life cycle of the entire application.
in conclusion
Dagger is a powerful dependent injection framework that helps us to achieve low -coupled synergy, high testability and maintenance code between modules.By mastering the core principles of the Dagger framework, we can elegantly rely on injects and improve the quality of code and development efficiency.
I hope this article will be helpful for everyone to learn and use the Dagger framework.If you want to learn more about the Dagger framework, please refer to the official Dagger document: https://dagger.dev/
