This talk will show how to use Dagger Multibindings, but more importantly why you should use it. We will will look at a typical Android use case and see why we should refactor it and how we can do so with Dagger Multibindings.

1. Dagger Multibinding
More the Why than the How

2. Dagger
@Provides
fun provideRectangle() = Rectangle()
@Inject
lateinit var rectangle: Rectangle

3. Multibindings
interface Shape
class Triangle: Shape
class Rectangle: Shape
class Circle: Shape

4. Set
@Binds
@IntoSet
fun provideRectangleShape(rectangle: Rectangle): Shape
@Binds
@IntoSet
fun provideTriangleShape(triangle: Triangle): Shape

5. Set
@Binds
@IntoSet
fun provideRectangleShape(rectangle: Rectangle): Shape
@Binds
@IntoSet
fun provideTriangleShape(triangle: Triangle): Shape
@Inject
lateinit var shapes: Set<Shape>

6. Map
@Binds
@IntoMap
@StringKey(RECTANGLE_KEY)
fun provideRectangleShape(rectangle: Rectangle): Shape
@Binds
@IntoMap
@StringKey(TRIANGLE_KEY)
fun provideTriangleShape(triangle: Triangle): Shape

7. Why
What the documentation says:
“You could use multibindings to implement a plugin architecture, for example,
where several modules can contribute individual plugin interface
implementations so that a central class can use the entire set of plugins”

8. Why
open/closed principle
“software entities (classes, modules, functions, etc.) should be open for
extension, but closed for modification”

9. Refactoring
Let’s see some code

10. Open-Closed principle
Open for extension:
We can easily add new view types to our adapter
Closed for modification:
We do not need to touch the existing adapter code to add a new type

11. When to use
Indicators:
● Repeating conditional
● Type codes, enums, …

12. When to use
Indicators:
● Repeating conditional
● Type codes, enums, …
… but it always depends

13. interface PaymentProvider {
fun pay()
fun isEnabled(): Boolean
}
ShareTheMeal Android App
ShareTheMeal Example

14. Ressources
Refactoring - Martin Fowler
Chapter : Replace conditionals with polymorphism
Clean Code - Robert C Martin
Chapter : Objects and Data Structures
Google Tech Talks
The clean code talks - Inheritance, Polymorphism & Testing

15. Thank you
@SophosAdriano
https://github.com/AdrianoCelentano/DaggerMultibindings
https://adrianocelentano.github.io/online-cv/