Le Composite est un patron de conception structurel qui permet d’agencer les objets dans une structure ressemblant à une arborescence, afin de pouvoir la traiter comme un objet individuel.
Le composite est devenu la solution la plus populaire pour régler les problèmes d’une structure arborescente. Il offre une fonctionnalité très pratique qui permet de parcourir récursivement toute l’arborescence et d’additionner les résultats.
Exemples d’utilisation : Le composite est très répandu en Swift. Il est souvent utilisé pour modéliser les hiérarchies des composants d’une interface utilisateur ou pour du code qui manipule des graphes.
Identification : Si vous avez une arborescence composée uniquement d’objets issus de la même hiérarchie de classes, c’est probablement un composite. Si les méthodes de ces classes délèguent les tâches aux objets enfants de l’arborescence et passent par une classe de base ou interface de la hiérarchie pour ce faire, il est très probable que ce soit réellement un composite.
Les exemples suivants sont disponibles sur le site de
Swift Playgrounds.
Félicitations à
Alejandro Mohamad pour avoir créé la version du Playground.
Exemple conceptuel
Dans cet exemple, nous allons voir la structure du Composite et répondre aux questions suivantes :
Que contiennent les classes ?
Quels rôles jouent-elles ?
Comment les éléments du patron sont-ils reliés ?
Après avoir étudié la structure du patron, vous pourrez plus facilement comprendre l’exemple suivant qui est basé sur un cas d’utilisation réel en Swift.
Example.swift: Exemple conceptuel
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: Résultat de l’exécution
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)
Analogie du monde réel
Example.swift: Analogie du monde réel
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: Résultat de l’exécution
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
