Dependency Injection on Android

Pedro V. Gómez Sánchez - [email protected] - @pedro_g_s - github.com/pedrovgs
Dependency Injection on Android Pedro Vicente Gómez Sánchez Senior Android Developer at Karumi [email protected] @pedro_g_s github.com/pedrovgs

Alberto Gragera Technical Director Jorge Barroso Senior Android Developer Davide Mendolia Senior Full Stack Engineer Sergio Gutierrez Senior Full Stack Engineer

Agenda • Introduction. • What can I do using Dependency Injection? • Scoped Graphs. • Dagger on Android. • Dagger 2.

Introduction Inversion 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.

Dependency Injection Example All the dependencies are passed in construction.

Dependency Injection Example The implementation details are part of the Dependency Injector configuration.

Dependency Injection Example 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 Android Step 1. Add Dagger and Dagger Compiler as dependencies:

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

Dagger on Android Step 3. Configure Dagger Modules:

Dagger on Android Step 4. Initialize your Application Object Graph:

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

Dagger on Android Step 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

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

Dependency Injection on Android

More Decks by Karumi

Featured

Transcript