Kompozyt w języku Swift
Kompozyt to strukturalny wzorzec projektowy umożliwiający komponowanie struktury drzewiastej z obiektów i traktowanie jej jak pojedynczy obiekt.
Kompozyt stał się dość popularnym rozwiązaniem wielu problemów gdzie w grę wchodzi struktura drzewa. Zaletą tego wzorca jest możliwość uruchamiania metod rekurencyjnie na wszystkich elementach struktury i sumowanie wyników ich działania.
Złożoność:
Popularność:
Przykłady użycia: Wzorzec Kompozyt jest dość powszechny w kodzie Swift. Często stosuje się go do modelowania hierarchii komponentów interfejsu użytkownika lub kodu który działa na grafach.
Identyfikacja: Jeśli klasy wszystkich obiektów w drzewie należą do jednej hierarchii to najprawdopodobniej mamy do czynienia z kompozytem. Jeśli dodatkowo metody tych klas delegują zadania obiektom-dzieciom wchodzącym w skład tego drzewa i robią to za pośrednictwem klasy bazowej lub bazowego interfejsu hierarchii, to na pewno jest to kompozyt.
Następujące przykłady są dostępne na Swift Playgrounds.
Gratulacje dla Alejandro Mohamad za stworzenie wersji Playground.
Przykład koncepcyjny
Poniższy przykład ilustruje strukturę wzorca Kompozyt ze szczególnym naciskiem na następujące kwestie:
- Z jakich składa się klas?
- Jakie role pełnią te klasy?
- W jaki sposób elementy wzorca są ze sobą powiązane?
Poznawszy strukturę wzorca będzie ci łatwiej zrozumieć następujący przykład, oparty na prawdziwym przypadku użycia Swift.
Example.swift: Przykład koncepcyjny
import XCTest /// The base Component class declares common operations for both simple and /// complex objects of a composition. protocol Component { /// The base Component may optionally declare methods for setting and /// accessing a parent of the component in a tree structure. It can also /// provide some default implementation for these methods. var parent: Component? { get set } /// In some cases, it would be beneficial to define the child-management /// operations right in the base Component class. This way, you won't need /// to expose any concrete component classes to the client code, even during /// the object tree assembly. The downside is that these methods will be /// empty for the leaf-level components. func add(component: Component) func remove(component: Component) /// You can provide a method that lets the client code figure out whether a /// component can bear children. func isComposite() -> Bool /// The base Component may implement some default behavior or leave it to /// concrete classes. func operation() -> String } extension Component { func add(component: Component) {} func remove(component: Component) {} func isComposite() -> Bool { return false } } /// The Leaf class represents the end objects of a composition. A leaf can't /// have any children. /// /// Usually, it's the Leaf objects that do the actual work, whereas Composite /// objects only delegate to their sub-components. class Leaf: Component { var parent: Component? func operation() -> String { return "Leaf" } } /// The Composite class represents the complex components that may have /// children. Usually, the Composite objects delegate the actual work to their /// children and then "sum-up" the result. class Composite: Component { var parent: Component? /// This fields contains the conponent subtree. private var children = [Component]() /// A composite object can add or remove other components (both simple or /// complex) to or from its child list. func add(component: Component) { var item = component item.parent = self children.append(item) } func remove(component: Component) { // ... } func isComposite() -> Bool { return true } /// The Composite executes its primary logic in a particular way. It /// traverses recursively through all its children, collecting and summing /// their results. Since the composite's children pass these calls to their /// children and so forth, the whole object tree is traversed as a result. func operation() -> String { let result = children.map({ $0.operation() }) return "Branch(" + result.joined(separator: " ") + ")" } } class Client { /// The client code works with all of the components via the base interface. static func someClientCode(component: Component) { print("Result: " + component.operation()) } /// Thanks to the fact that the child-management operations are also /// declared in the base Component class, the client code can work with both /// simple or complex components. static func moreComplexClientCode(leftComponent: Component, rightComponent: Component) { if leftComponent.isComposite() { leftComponent.add(component: rightComponent) } print("Result: " + leftComponent.operation()) } } /// Let's see how it all comes together. class CompositeConceptual: XCTestCase { func testCompositeConceptual() { /// This way the client code can support the simple leaf components... print("Client: I've got a simple component:") Client.someClientCode(component: Leaf()) /// ...as well as the complex composites. let tree = Composite() let branch1 = Composite() branch1.add(component: Leaf()) branch1.add(component: Leaf()) let branch2 = Composite() branch2.add(component: Leaf()) branch2.add(component: Leaf()) tree.add(component: branch1) tree.add(component: branch2) print("\nClient: Now I've got a composite tree:") Client.someClientCode(component: tree) print("\nClient: I don't need to check the components classes even when managing the tree:") Client.moreComplexClientCode(leftComponent: tree, rightComponent: Leaf()) } } Output.txt: Wynik działania
Client: I've got a simple component: Result: Leaf Client: Now I've got a composite tree: Result: Branch(Branch(Leaf Leaf) Branch(Leaf Leaf)) Client: I don't need to check the components classes even when managing the tree: Result: Branch(Branch(Leaf Leaf) Branch(Leaf Leaf) Leaf) Przykład z prawdziwego życia
Example.swift: Przykład z prawdziwego życia
import UIKit import XCTest protocol Component { func accept<T: Theme>(theme: T) } extension Component where Self: UIViewController { func accept<T: Theme>(theme: T) { view.accept(theme: theme) view.subviews.forEach({ $0.accept(theme: theme) }) } } extension UIView: Component {} extension UIViewController: Component {} extension Component where Self: UIView { func accept<T: Theme>(theme: T) { print("\t\(description): has applied \(theme.description)") backgroundColor = theme.backgroundColor } } extension Component where Self: UILabel { func accept<T: LabelTheme>(theme: T) { print("\t\(description): has applied \(theme.description)") backgroundColor = theme.backgroundColor textColor = theme.textColor } } extension Component where Self: UIButton { func accept<T: ButtonTheme>(theme: T) { print("\t\(description): has applied \(theme.description)") backgroundColor = theme.backgroundColor setTitleColor(theme.textColor, for: .normal) setTitleColor(theme.highlightedColor, for: .highlighted) } } protocol Theme: CustomStringConvertible { var backgroundColor: UIColor { get } } protocol ButtonTheme: Theme { var textColor: UIColor { get } var highlightedColor: UIColor { get } /// other properties } protocol LabelTheme: Theme { var textColor: UIColor { get } /// other properties } /// Button Themes struct DefaultButtonTheme: ButtonTheme { var textColor = UIColor.red var highlightedColor = UIColor.white var backgroundColor = UIColor.orange var description: String { return "Default Buttom Theme" } } struct NightButtonTheme: ButtonTheme { var textColor = UIColor.white var highlightedColor = UIColor.red var backgroundColor = UIColor.black var description: String { return "Night Buttom Theme" } } /// Label Themes struct DefaultLabelTheme: LabelTheme { var textColor = UIColor.red var backgroundColor = UIColor.black var description: String { return "Default Label Theme" } } struct NightLabelTheme: LabelTheme { var textColor = UIColor.white var backgroundColor = UIColor.black var description: String { return "Night Label Theme" } } class CompositeRealWorld: XCTestCase { func testCompositeRealWorld() { print("\nClient: Applying 'default' theme for 'UIButton'") apply(theme: DefaultButtonTheme(), for: UIButton()) print("\nClient: Applying 'night' theme for 'UIButton'") apply(theme: NightButtonTheme(), for: UIButton()) print("\nClient: Let's use View Controller as a composite!") /// Night theme print("\nClient: Applying 'night button' theme for 'WelcomeViewController'...") apply(theme: NightButtonTheme(), for: WelcomeViewController()) print() print("\nClient: Applying 'night label' theme for 'WelcomeViewController'...") apply(theme: NightLabelTheme(), for: WelcomeViewController()) print() /// Default Theme print("\nClient: Applying 'default button' theme for 'WelcomeViewController'...") apply(theme: DefaultButtonTheme(), for: WelcomeViewController()) print() print("\nClient: Applying 'default label' theme for 'WelcomeViewController'...") apply(theme: DefaultLabelTheme(), for: WelcomeViewController()) print() } func apply<T: Theme>(theme: T, for component: Component) { component.accept(theme: theme) } } class WelcomeViewController: UIViewController { class ContentView: UIView { var titleLabel = UILabel() var actionButton = UIButton() override init(frame: CGRect) { super.init(frame: frame) setup() } required init?(coder decoder: NSCoder) { super.init(coder: decoder) setup() } func setup() { addSubview(titleLabel) addSubview(actionButton) } } override func loadView() { view = ContentView() } } /// Let's override a description property for the better output extension WelcomeViewController { open override var description: String { return "WelcomeViewController" } } extension WelcomeViewController.ContentView { override var description: String { return "ContentView" } } extension UIButton { open override var description: String { return "UIButton" } } extension UILabel { open override var description: String { return "UILabel" } } Output.txt: Wynik działania
Client: Applying 'default' theme for 'UIButton' UIButton: has applied Default Buttom Theme Client: Applying 'night' theme for 'UIButton' UIButton: has applied Night Buttom Theme Client: Let's use View Controller as a composite! Client: Applying 'night button' theme for 'WelcomeViewController'... ContentView: has applied Night Buttom Theme UILabel: has applied Night Buttom Theme UIButton: has applied Night Buttom Theme 
