CircularDependencies.md

Circular Dependencies

Circular Dependencies are dependencies of instances that depend on each other. To define Circular Dependencies by Swinject, either of the dependencies must be injected through the property.

Initializer/Property Dependencies

Assume that you have Parent and Child classes depending on each other. Parent depends on ChildType through its initializer, and Child on ParentType through its property. The back-reference from Child to ParentType is a weak property to avoid memory leak.

protocol ParentType: AnyObject { }
protocol ChildType: AnyObject { }

class Parent: ParentType {
    let child: ChildType?

    init(child: ChildType?) {
        self.child = child
    }
}

class Child: ChildType {
    weak var parent: ParentType?
}

The Circular Dependencies are defined as below.

let container = Container()
container.register(ParentType.self) { r in
    Parent(child: r.resolve(ChildType.self)!)
}
container.register(ChildType.self) { _ in Child() }
    .initCompleted { r, c in
        let child = c as! Child
        child.parent = r.resolve(ParentType.self)
    }

Here the injection to the parent property of Child must be specified in the initCompleted callback to get rid of infinite recursive calls.

Property/Property Dependencies

Similarly, assume that you have the following classes depending through each property.

protocol ParentType: AnyObject { }
protocol ChildType: AnyObject { }

class Parent: ParentType {
    var child: ChildType?
}

class Child: ChildType {
    weak var parent: ParentType?
}

The Circular Dependencies are defined as below.

    let container = Container()
    container.register(ParentType.self) { r in
        let parent = Parent()
        parent.child = r.resolve(ChildType.self)!
        return parent
    }
    container.register(ChildType.self) { _ in Child() }
        .initCompleted { r, c in
            let child = c as! Child
            child.parent = r.resolve(ParentType.self)
        }

Here the both or either of the depending properties must be specified in the initCompleted callback to get rid of infinite recursive calls.

Initializer/Initializer Dependencies

Not supported. This type of dependencies causes infinite recursive calls.

Next page: Container Hierarchy

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