Dependency injection on Android - Spanish

Pedro V. Gómez Sánchez - [email protected] - @pedro_g_s - github.com/pedrovgs

Dependency Injection on AndroidPedro Vicente Gómez SánchezSenior Android Developer at Karumi

[email protected]@pedro_g_sgithub.com/pedrovgs

mailto:[email protected]


Alberto GrageraTechnical Director

Jorge BarrosoSenior Android Developer

Davide MendoliaSenior Full Stack Engineer

Sergio GutierrezSenior Full Stack Engineer



Agenda● Introduction.

● What can I do using Dependency Injection?

● Scoped Graphs.

● Dagger on Android.

● Dagger 2.



IntroductionInversion of Control

vs

Dependency Inversion

vs

Dependency Injection



Inversion of Control

The natural evolution of the structured and imperative programming and the usage of reusable frameworks.

The execution point where you software takes the control is not defined by your software.



Dependency Inversion

One of the most important S.O.L.I.D principles.

Depend on abstractions, forget about implementation details.

Provide implementation details depending on abstractions can be tedious.



Dependency Injection

Software Design Pattern used to facilitate the usage of Dependency Inversion.

Provides dependencies given some previous configuration where abstractions are linked with

concretions.



Why?

The usage of IoC, Dependency Inversion and Dependency Injection provides give us the following benefits:

● Testability.● Decoupling.● Modularity.



Show me the code!



Dependency Injection Example

The presenter inside this fragment has to be instantiated with all the dependency tree. Without a dependency

injector this can be tedious.




All the dependencies are passed in construction.




The implementation details are part of the Dependency Injector configuration.




Now the Presenter is injected into the Fragment.



What can I do with a Dependency Injector?



What can I do?● Do not link the class to the runtime lifecycle or frameworks.

● Improve testability.

● Decouple your code and improve our software design.

● Detect code smells related to class dependencies and SRP violations.

● Change the implementation details in build time.

● Extract implementation details out of the business logic.



What can I do?Do not link the class to the runtime lifecycle.



What can I do?Improve testability.



What can I do?Detect code smells related to class dependencies and single responsibility principle violations.



What can I do?Change the implementation details in build time.



What can I do?Decouple your code and improve our software design.

Using a Dependency Injector combined with the correct usage of Dependency Inversion we can easily develop the same feature at the

same time in different teams and layers.



What can I do?Extract implementation details out of the business logic.

Develop software being agnostic of the Framework or the Runtime used. Implementation details are provided using the dependency injector and

your business logic does not depend on it.



What can I do?The dependency container provide us different configurations to provide dependencies:

● Singletons.

● Lazy Initialization.

● Provided dependencies.

● Named dependencies.

● Override dependencies already configured.

● Custom qualifiers.



What can I do?Singletons



What can I do?Lazy Initialization



What can I do?Provided dependencies



What can I do?Named Dependencies



What can I do?Custom Qualifiers



Scoped Graphs



Scoped Graphs

Dependencies provided by the Dependency Container or Object Graph inside the Application class are linked to the Application lifecycle.

We need more than one graph to improve the Dependency Injector usage and performance.

At the same time, some dependencies are needed just when some components like Activities or Custom Views are initialized.



Scoped Graphs

Application Graph

Activity A Graph

Activity B Graph

Create Activity A

Create Activity B



Dagger on Android



Dagger on AndroidStep 1. Add Dagger and Dagger Compiler as dependencies:



Dagger on AndroidStep 2. Create an Application extension and configure the Object Graph:



Dagger on AndroidStep 3. Configure Dagger Modules:



Dagger on AndroidStep 4. Initialize your Application Object Graph:



Dagger on AndroidStep 5. Create a method to extend the Application Object Graph:



Dagger on AndroidStep 6. Create a BaseActivity with the code needed to extend the

Application Graph.



Step 7. Create an abstract method requesting the Activity modules:

Dagger on Android



Step 8. Extend the Application Object Graph using the Activity modules:

Dagger on Android



https://www.github.com/pedrovgs/EffectiveAndroidUI



Can you repeat, please?

Dependency Injection on Android Workshop


https://www.youtube.com/watch?v=ONziKX93iTM

https://www.youtube.com/watch?v=ONziKX93iTM


Dagger 2



Dagger 2

● Configuration based on components not in graphs.

● Generated code is now something you can read.

● Reflection free.

● 13 % faster.

● Full graph validated in build time.



Questions?


Dependency injection on Android - Spanish

Engineering

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