组合模式能够使容器与内容具有一致性，创造出递归结构，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.png

Leaf(树叶):表示叶节点对象，叶子节点没有子节点，不能放入其他对象.

Composite(复合物): 可以存储Leaf对象，也可以存储Composite对象，相当于容器.

Component : 组合中的对象声明接口, 定义Leaf与Compostite的公共行为接口.

现实生活中最符合组合模式结构的莫过于文件系统，文件类似于Leaf，文件夹类似于Composite.

核心代码:

class Entry {
    
    var parent:Directory?
    var name:String?
    
    convenience init(name:String,parent:Directory?) {
        self.init()
        self.name = name
        self.parent = parent
    }
    
    func addEntry(entry:Entry) {}
    
    func deleteEntry(entry:Entry) {}
    
    func printnEntry() {}
    
    func printEntry(prefix:String) {}
    
}

class File:Entry {
    
    
    override func printnEntry() {
        print("目录:\(String(describing: self.parent!.name!))/\(String(describing: self.name!))")
    }
    
    override func printEntry(prefix: String) {
         print("目录:\(prefix)/\(String(describing: self.parent!.name!))/\(String(describing: self.name!))")
    }
}

class Directory: Entry {
    
    var files = [File]()
    var dirs =  [Directory]()
    
    override func addEntry(entry: Entry) {
        if entry is File {
            files.append(entry as! File)
        } else {
            dirs.append(entry as! Directory)
        }
    }
    
     override func deleteEntry(entry:Entry) {
        
        if entry is File {
            for i in 0..<files.count {
                if entry.name == files[i].name {
                    files.remove(at: i)
                }
            }
        } else {
            for i in 0..<dirs.count {
                if entry.name == dirs[i].name {
                    dirs.remove(at: i)
                }
            }
        }
    }
    
    override func printnEntry() {
        
        for file in files {
            file.printnEntry()
        }
        
        for dir in dirs {
            for file in dir.files {
                file.printEntry(prefix: self.name!)
            }
        }
    }
    
}

测试代码:

       let rootDir:Directory = Directory(name: "root", parent: nil)
        
        let file:File = File(name: "study.html", parent: rootDir)
        let file2:File = File(name: "readme.txt", parent: rootDir)
        
        let studyDir:Directory = Directory(name: "study", parent: rootDir)
        let file3:File = File(name: "composite.swift", parent: studyDir)
        let file4:File = File(name: "study.project", parent: studyDir)
        
        rootDir.addEntry(entry: file)
        rootDir.addEntry(entry: file2)
        rootDir.addEntry(entry: studyDir)
        
        studyDir.addEntry(entry: file3)
        studyDir.addEntry(entry: file4)
    
        rootDir.printnEntry()
        
        print("FlyElephant---删除文件夹")
        rootDir.deleteEntry(entry:studyDir)
        rootDir.printnEntry()
        
        print("FlyElephant---删除文件")
        rootDir.deleteEntry(entry:file2)
        rootDir.printnEntry()

FlyElephant.png

组合模式定义由 Leaf 对象和 Composite 对象组成的类结构，调用简单，添加或删除子部件变得很容易.