设计模式-15.组合模式

一句话总结

将对象组合成树形结构以表示“部分-整体”的层次结构。组合模式使用户对单个对象和组合对象的适用具有一致性。

Code

static func main() {
    let root = Composite(name: "root")
    root.add(c: Leaf(name: "leaf a"))
    root.add(c: Leaf(name: "leaf b"))

    let comp = Composite(name: "x")
    comp.add(c: Leaf(name: "leaf xa"))
    comp.add(c: Leaf(name: "leaf xb"))

    root.add(c: comp)

    let comp2 = Composite(name: "xx")
    comp2.add(c: Leaf(name: "leaf xxa"))
    comp2.add(c: Leaf(name: "leaf xxb"))

    comp.add(c: comp2)

    root.add(c: Leaf(name: "leaf c"))

    let leaf = Leaf(name: "leaf d")
    root.add(c: leaf)
    root.remove(c: leaf)

    root.display(depth: 1)

}

protocol Component {
    var name: String { get set }
    
    func add(c: Component)
    func remove(c: Component)
    func display(depth: Int)
}

class Leaf: Component {
    var name: String

    init(name: String) {
        self.name = name
    }

    func add(c: Component) {
        print("Cannot add to a leaf")
    }

    func remove(c: Component) {
        print("Cannot remove from a leaf")
    }

    func display(depth: Int) {
        var depthString = ""
        for _ in 1...depth {
            depthString.append("-")
        }

        print(depthString + name)
    }
}

class Composite: Component {
    var name: String
    var children: [Component] = []

    init(name: String) {
        self.name = name
    }

    func add(c: Component) {
        children.append(c)
    }

    func remove(c: Component) {
        children.removeAll { (component) -> Bool in
            component.name == c.name
        }
    }

    func display(depth: Int) {
        var depthString = ""
        for _ in 1...depth {
            depthString.append("-")
        }

        print(depthString + name)
        for item in children {
            item.display(depth: depth + 2)
        }
    }  
}

何时使用

需求中是体现部分和整体的层次结构时。比如：具有各地办事处的公司组织，view的树形结构