Initializer Injection is a pattern to pass dependencies to a dependent instance by its initializer. Initializer Injection is appropriate if the dependent instance cannot work without the dependencies.
The following code defines Initializer Injection to PetOwner, which depends on AnimalType.
let container = Container()
container.register(AnimalType.self) { _ in Cat() }
container.register(PersonType.self) { r in
PetOwner(pet: r.resolve(AnimalType.self)!)
}
Where the protocols and classes are
protocol AnimalType {
func sound() -> String
}
class Cat: AnimalType {
init() { }
func sound() -> String {
return "Meow"
}
}
protocol PersonType { }
class PetOwner: PersonType {
let pet: AnimalType
init(pet: AnimalType) {
self.pet = pet
}
}
Note that the actual type of AnimalType passed to the initializer of PetOwner is automatically resolved by Swinject when PetOwner instance is created.
Property Injection is a pattern to pass a dependency to a dependent instance by its setter property. Property Injection is appropriate if the dependency is optional to the dependent instance.
The following code defines Property Injection to PetOwner2.
let container = Container()
container.register(AnimalType.self) { _ in Cat() }
container.register(PersonType.self) { r in
let owner = PetOwner2()
owner.pet = r.resolve(AnimalType.self)
return owner
}
Where
class PetOwner2: PersonType {
var pet: AnimalType?
init() { }
}
Or you can use initCompleted callback instead of defining the injection in the registration closure.
let container = Container()
container.register(AnimalType.self) { _ in Cat() }
container.register(PersonType.self) { _ in PetOwner2() }
.initCompleted { r, p in
let owner = p as! PetOwner2
owner.pet = r.resolve(AnimalType.self)
}
Method Injection is a similar pattern to Property Injection, but it uses a method to pass dependencies to a dependent instance.
The following code defines Property Injection to PetOwner3.
let container = Container()
container.register(AnimalType.self) { _ in Cat() }
container.register(PersonType.self) { r in
let owner = PetOwner3()
owner.setPet(r.resolve(AnimalType.self)!)
return owner
}
Where
class PetOwner3: PersonType {
var pet: AnimalType?
init() { }
func setPet(pet: AnimalType) {
self.pet = pet
}
}
Or you can use initCompleted callback instead of defining the injection in the registration closure.
let container = Container()
container.register(AnimalType.self) { _ in Cat() }
container.register(PersonType.self) { _ in PetOwner3() }
.initCompleted { r, p in
let owner = p as! PetOwner3
owner.setPet(r.resolve(AnimalType.self)!)
}