Dagger 2 is a dependency injection framework created by Google to address issues with previous solutions like Dagger 1. It aims to generate object graphs at compile time instead of using reflection at runtime, making the code faster and allowing errors to be detected earlier. It uses annotations like @Inject, @Module and @Component to identify dependencies and generate implementation code. If any dependencies cannot be satisfied, it fails to compile rather than causing runtime errors. The documentation recommends proceeding with caution as Dagger 2 is still in pre-alpha stage.

1. Dagger 2
Dino Kovač

2. What is dependency injection?

3. What is dependency injection?

4. Why dependency injection?
• More reusable code
• More readable code
• More testable code

5. Dependency graph
• Why not do it
manually?

6. Problems of past DI solutions
• Runtime failures in case of unsatisfied
dependencies
• Difficult debugging
• Huge unhelpful stack traces
• Untraceable program flow
• Slow because of reflection

7. Dagger 1
• Made by ex-googlers at Square
• Reflection used only to generate the object graph,
code generated for object instantiation
• Lots of problems detected at compile time

8. Dagger 2
• Fork of Dagger 1 by the Java Core Libraries team at Google
• Dagger 2.0 is pre-alpha and should be used with caution,
though it is usable.
• Goals
• Make it fast (eliminate reflection)
• Make generated code readable
• Fail as early as possible (compile time)

9. Requesting dependencies
• @Inject annotation
• field
• constructor
• method

10. Providing dependencies
• @Module annotated
classes
• @Provider annotated
methods

11. Building the dependency graph
• @Component annotates
an interface which
provides a contract
• Dagger 2 generates an
implementation of that
contract

12. What if we’re missing a dependency?
• it doesn’t compile!
• error: Heater cannot be provided without an
@Provides-annotated method.
CoffeeMaker.<init>(Heater heater, Pump pump)
[parameter: Heater heater]

13. When can I use it?
• Soon.
• Currently 2.0-SNAPSHOT
• Dagger 2.0 is pre-alpha and should be used with
caution, though it is usable.

14. More
• http://square.github.io/dagger/
• http://google.github.io/dagger/
• Dagger 2 - A new type of dependency injection
• https://www.youtube.com/watch?
v=oK_XtfXPkqw