NSOutlineView 中托管 NSView 的层

使用 NSOutlineView 来托管 NSView 的层是在 macOS 开发中常见的一种技术。NSOutlineView 是一种可以显示层级数据的视图控件，而 NSView 是 macOS 中用于绘制用户界面的基本元素。通过将 NSView 放置在 NSOutlineView 中的不同层级中，我们可以实现多级菜单、文件浏览器等功能。下面将介绍如何使用 NSOutlineView 托管 NSView 的层，并提供一个简单的案例代码。

swift
class MyOutlineViewDataSource: NSObject, NSOutlineViewDataSource {
    // 实现数据源方法
}
class MyOutlineViewDelegate: NSObject, NSOutlineViewDelegate {
    // 实现代理方法
}
let outlineView = NSOutlineView()
outlineView.dataSource = MyOutlineViewDataSource()
outlineView.delegate = MyOutlineViewDelegate()

swift
class Node {
    var name: String
    var subnodes: [Node]
    
    init(name: String, subnodes: [Node] = []) {
        self.name = name
        self.subnodes = subnodes
    }
}

swift
class MyOutlineViewDataSource: NSObject, NSOutlineViewDataSource {
    var rootNodes: [Node]
    
    init(rootNodes: [Node]) {
        self.rootNodes = rootNodes
    }
    
    // 返回根节点的数量
    func outlineView(_ outlineView: NSOutlineView, numberOfChildrenOfItem item: Any?) -> Int {
        if item == nil {
            return rootNodes.count
        }
        
        if let node = item as? Node {
            return node.subnodes.count
        }
        
        return 0
    }
    
    // 返回指定索引的子节点
    func outlineView(_ outlineView: NSOutlineView, child index: Int, ofItem item: Any?) -> Any {
        if item == nil {
            return rootNodes[index]
        }
        
        if let node = item as? Node {
            return node.subnodes[index]
        }
        
        fatalError("Invalid item")
    }
    
    // 判断节点是否为叶子节点
    func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
        if let node = item as? Node {
            return !node.subnodes.isEmpty
        }
        
        return false
    }
    
    // 返回节点对应的视图
    func outlineView(_ outlineView: NSOutlineView, viewFor tableColumn: NSTableColumn?, item: Any) -> NSView? {
        // 返回自定义的 NSView，用于绘制节点的内容
    }
}

swift
class MyOutlineViewDelegate: NSObject, NSOutlineViewDelegate {
    // 实现代理方法
}

swift
// 定义文件系统节点的数据模型
class FileSystemNode {
    var name: String
    var isFolder: Bool
    var subnodes: [FileSystemNode]
    
    init(name: String, isFolder: Bool, subnodes: [FileSystemNode] = []) {
        self.name = name
        self.isFolder = isFolder
        self.subnodes = subnodes
    }
}
// 数据源
class FileSystemOutlineDataSource: NSObject, NSOutlineViewDataSource {
    var rootNodes: [FileSystemNode]
    
    init(rootNodes: [FileSystemNode]) {
        self.rootNodes = rootNodes
    }
    
    func outlineView(_ outlineView: NSOutlineView, numberOfChildrenOfItem item: Any?) -> Int {
        if item == nil {
            return rootNodes.count
        }
        
        if let node = item as? FileSystemNode {
            return node.subnodes.count
        }
        
        return 0
    }
    
    func outlineView(_ outlineView: NSOutlineView, child index: Int, ofItem item: Any?) -> Any {
        if item == nil {
            return rootNodes[index]
        }
        
        if let node = item as? FileSystemNode {
            return node.subnodes[index]
        }
        
        fatalError("Invalid item")
    }
    
    func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
        if let node = item as? FileSystemNode {
            return node.isFolder && !node.subnodes.isEmpty
        }
        
        return false
    }
    
    func outlineView(_ outlineView: NSOutlineView, viewFor tableColumn: NSTableColumn?, item: Any) -> NSView? {
        let view = outlineView.makeView(withIdentifier: NSUserInterfaceItemIdentifier("Cell"), owner: self) as? NSTableCellView
        
        if let fileSystemNode = item as? FileSystemNode {
            view?.textField?.stringValue = fileSystemNode.name
            view?.imageView?.image = fileSystemNode.isFolder ? NSImage(named: NSImage.folderName) : NSImage(named: NSImage.genericDocumentName)
        }
        
        return view
    }
}
// 代理
class FileSystemOutlineDelegate: NSObject, NSOutlineViewDelegate {
    func outlineView(_ outlineView: NSOutlineView, heightOfRowByItem item: Any) -> CGFloat {
        return 20.0
    }
    
    func outlineView(_ outlineView: NSOutlineView, isGroupItem item: Any) -> Bool {
        return false
    }
    
    func outlineViewSelectionDidChange(_ notification: Notification) {
        // 处理选中节点变化的逻辑
    }
}
// 创建 NSOutlineView
let outlineView = NSOutlineView()
outlineView.dataSource = FileSystemOutlineDataSource(rootNodes: [
    FileSystemNode(name: "Documents", isFolder: true, subnodes: [
        FileSystemNode(name: "README.txt", isFolder: false),
        FileSystemNode(name: "Images", isFolder: true, subnodes: [
            FileSystemNode(name: "image1.jpg", isFolder: false),
            FileSystemNode(name: "image2.jpg", isFolder: false)
        ])
    ]),
    FileSystemNode(name: "Projects", isFolder: true, subnodes: [
        FileSystemNode(name: "Project1", isFolder: true, subnodes: [
            FileSystemNode(name: "File1.swift", isFolder: false),
            FileSystemNode(name: "File2.swift", isFolder: false)
        ]),
        FileSystemNode(name: "Project2", isFolder: true, subnodes: [
            FileSystemNode(name: "File1.swift", isFolder: false),
            FileSystemNode(name: "File2.swift", isFolder: false)
        ])
    ])
])
outlineView.delegate = FileSystemOutlineDelegate()