Dependency injection using dagger 2
Download as PPTX, PDF0 likes160 views
This document discusses dependency injection using Dagger 2. It begins by defining dependency injection as objects defining and supplying dependencies for other objects, implementing the inversion of control principle. It then discusses the dependency inversion principle of depending on abstractions rather than implementations. Next, it introduces Dagger 2 as a compile-time dependency injection framework maintained by Google. It proceeds to explain how to build a dependency graph with Dagger 2 by making module and component classes, using dependency annotations like @Inject and @Provide, and handling scoped objects and qualifiers. The document concludes by referencing additional resources on dependency injection and Dagger 2.
Dependency injection using dagger 2
- 2. Dependency Injection Using Dagger 2 Mahmoud El-Naggar
- 3. Content 1. Dependency Injection Definition and Importance 2. Dependency Inversion Principle (SOLID Principles) 3. What and Why Dagger 2 ? 4. Building Dependency Graph
- 4. Dependency Injection Definition and Importance Definition : Object defines and Supply dependencies for another Object. It is implementation of the Inversion of Control Principal(IoC) that state each class must get its dependencies from outside. Importance : 1- Decouple the objects from each others and make the Classes more abstracted. 2- simplifying the Unit Test
- 5. The Problem. Here the problem is Car class depend on Engine Class so they are tightly coupled , if we want to change the Engine we have to change the Car too
- 7. The Solution Here instead of initialize the Engine Object Inside the Car , We Inject it to the Car from Outside. We delegated the creation of the Engine Object to another object so we can inject any Engine object even mock objects
- 8. Dependency Inversion Principle (DIP) This principle means class depends on abstraction not implementation.
- 9. The problem. Let's say we want to change the Engine to GasEngine ,then we have to change Car class and replace all The Engine to GasEngine
- 10. The Solution. According to DIP ,Class depend On Abstractions not the implementations
- 11. The Solution.
- 12. What is Dagger 2 ? Dagger is a fully static, compile-time dependency injection framework for both Java and Android. It is an adaptation of an earlier version created by Square and now maintained by Google.
- 13. Building Dependency Graph (Version +2.10) 1. Dagger Flow 2. Injecting Activity object 3. Scoped Objects 4. Qualifiers
- 14. Building Dependency Graph 1. Make a Module class annotated with @Module Annotation 2. Annotate each method that return a dependency with @Provide Annotation 3. Make an Interface annotated with @Component 4. Specify which Module will be used with this Component interface 5. Use @Inject Annotation to inject dependency when needed
- 15. Subcomponents Subcomponents are components that inherit and extend the object graph of a parent component. You can use them to partition your application’s object graph into subgraphs either to encapsulate different parts of your application from each other or to use more than one scope within a component. 1. Declaring a subcomponent 2. Adding a subcomponent to a parent component
- 16. Injecting Activity object 1. Install AndroidInjectionModule in your application component to ensure that all bindings necessary for these base types are available. 1. Start off by writing a @Subcomponent that extends AndroidInjector<YourActivity>, with a @Subcomponent.Builder that extends AndroidInjector.Builder<YourActivity> 1. After defining the subcomponent, add it to your component hierarchy by defining a module that binds the subcomponent builder and adding it to the component that injects your Application:
- 17. 4. Next, make your Application implement HasActivityInjector and @Inject a DispatchingAndroidInjector<Activity> to return from the activityInjector() method: 4. Finally, in your Activity.onCreate() method, call AndroidInjection.inject(this) before calling super.onCreate()
- 18. Scoped Objects Keep the objects among defined scope Scope are user defined annotations like ActivityScope ,UserScope and ApplicationScope
- 19. Qualifiers Dagger may not be able to disguish between returned objec from same Type Like ‘return context’ or ‘return getApplicationContext’
- 20. References 1. http://tutorials.jenkov.com/dependency-injection/index.html 2. https://google.github.io/dagger/ 3. https://dzone.com/articles/an-introduction-to-dagger-2-android-di-part-1- 3?fromrel=true 4. https://www.youtube.com/playlist?list=PLuR1PJnGR-Ih- HXnGSpnqjdhdvqcwhfFU 5. https://www.youtube.com/playlist?list=PLuR1PJnGR- IgeDuzxoGe3hHV_8OfbHy8c
- 21. Time for Questions :)