SwiftUI转Cocoa：窗口无显示及跨视图变量修改问题咨询

一、先修复窗口不显示及视图异常问题 #

你的代码存在几个关键错误，导致窗口内容无法正常显示：

1. 在draw(_:)方法中添加子视图：draw会在窗口重绘时频繁触发，每次调用都会重复添加按钮和CustomView2，造成视图层级混乱。子视图应该在视图初始化阶段创建并添加。
2. 重复创建CustomView2实例：AppDelegate中创建了一个customView2添加到窗口，同时CustomView1内部又创建了另一个实例，点击按钮修改的是内部不可见的实例，窗口上的标签自然不会变化。
3. 子视图布局超出范围：CustomView1内部的customView2位置设置不合理，导致其超出父视图可视范围，无法被看到。

二、视图间通信的正确实现（以闭包回调为例） #

闭包是Swift中简单直接的视图通信方式，类似SwiftUI的回调逻辑。以下是修复后的完整代码：

main.swift（无需修改） #

import Cocoa

let app = NSApplication.shared
 
let appDelegate = App2()
app.delegate = appDelegate
app.setActivationPolicy(.regular)
app.activate(ignoringOtherApps:true)
app.run()

App2.swift #

import Cocoa

class App2: NSObject, NSApplicationDelegate {
    var window: NSWindow!
    var customView1: CustomView1!
    var customView2: CustomView2!
    
    func buildMenu() {
        let mainMenu = NSMenu()
        NSApp.mainMenu = mainMenu
        let appMenuItem = NSMenuItem()
        mainMenu.addItem(appMenuItem)
        let appMenu = NSMenu()
        appMenuItem.submenu = appMenu
        appMenu.addItem(withTitle: "Quit", action:#selector(NSApplication.terminate), keyEquivalent: "q")
    }
    
    func buildWnd() {
        let _wndW: CGFloat = 400
        let _wndH: CGFloat = 400
        let appTitle: String = "app title"
        
        window = NSWindow(contentRect: NSMakeRect(0, 0, _wndW, _wndH), 
                          styleMask: [.titled, .closable, .miniaturizable, .resizable], 
                          backing: .buffered, 
                          defer: false)
        window.center()
        window.title = appTitle
        window.makeKeyAndOrderFront(window)
        
        // 创建两个自定义视图
        customView2 = CustomView2(frame: NSRect(x: 10, y: 100, width: 120, height: 50))
        customView1 = CustomView1(frame: NSRect(x: 10, y: 50, width: 120, height: 50))
        
        // 设置按钮点击回调，修改CustomView2的标签内容
        customView1.onButtonClick = {
            self.customView2.label.stringValue = "Button clicked!"
        }
        
        window.contentView?.addSubview(customView1)
        window.contentView?.addSubview(customView2)
    }
    
    class CustomView1: NSView {
        // 定义闭包作为点击回调
        var onButtonClick: (() -> Void)?
        
        override init(frame frameRect: NSRect) {
            super.init(frame: frameRect)
            setupSubviews()
        }
        
        required init?(coder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
        
        private func setupSubviews() {
            // 创建按钮并添加到视图
            let button = NSButton(frame: NSRect(x: 10, y: 10, width: 100, height: 30))
            button.title = "Click me!"
            button.bezelStyle = .rounded
            button.target = self
            button.action = #selector(buttonClicked(_:))
            self.addSubview(button)
        }
        
        @objc func buttonClicked(_ sender: NSButton) {
            // 触发回调
            onButtonClick?()
        }
    }
    
    class CustomView2: NSView {
        let label = NSTextField(frame: NSRect(x: 10, y: 10, width: 100, height: 20))
        
        override init(frame frameRect: NSRect) {
            super.init(frame: frameRect)
            setupLabel()
        }
        
        required init?(coder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
        
        private func setupLabel() {
            label.stringValue = "Hello, world!"
            label.isEditable = false
            label.isSelectable = false
            label.isBezeled = false
            label.drawsBackground = false
            self.addSubview(label)
        }
    }
    
    func applicationDidFinishLaunching(_ notification: Notification) {
        buildMenu()
        buildWnd()
    }
    
    func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
        return true
    }
}

三、其他常用的视图通信方式 #

1. 代理模式 #

适合复杂交互场景，通过协议定义交互规则：

protocol CustomView1Delegate: AnyObject {
    func buttonDidClick()
}

class CustomView1: NSView {
    weak var delegate: CustomView1Delegate?
    
    @objc func buttonClicked(_ sender: NSButton) {
        delegate?.buttonDidClick()
    }
}

// 在AppDelegate中实现代理
class App2: NSObject, NSApplicationDelegate, CustomView1Delegate {
    func buildWnd() {
        // ...
        customView1.delegate = self
    }
    
    func buttonDidClick() {
        customView2.label.stringValue = "Button clicked via delegate!"
    }
}

2. 通知中心（NSNotificationCenter） #

适合跨层级、多视图响应同一事件的场景：

// 在CustomView1中发送通知
@objc func buttonClicked(_ sender: NSButton) {
    NotificationCenter.default.post(name: NSNotification.Name("ButtonClicked"), object: nil)
}

// 在CustomView2中监听通知
class CustomView2: NSView {
    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        setupLabel()
        NotificationCenter.default.addObserver(self, selector: #selector(updateLabel), name: NSNotification.Name("ButtonClicked"), object: nil)
    }
    
    @objc private func updateLabel() {
        label.stringValue = "Button clicked via notification!"
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
}

3. 绑定（NSBinding） #

类似SwiftUI的状态管理，适用于KVC兼容的属性：

// 在CustomView2中绑定标签内容到属性
class CustomView2: NSView {
    @objc dynamic var labelText: String = "Hello, world!"
    
    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        setupLabel()
        label.bind(.value, to: self, withKeyPath: #keyPath(labelText), options: nil)
    }
}

// 在回调中修改属性，自动更新标签
customView1.onButtonClick = {
    self.customView2.labelText = "Button clicked via binding!"
}

内容的提问来源于stack exchange，提问作者KanKonga