跟踪NSWindow focus？(Swift，macOS)

class WindowDelegate: NSObject, NSWindowDelegate {
    // 实现协议方法
}

let window = NSWindow(contentRect: NSRect(x: 0, y: 0, width: 800, height: 600),
                      styleMask: [.titled, .closable, .miniaturizable, .resizable],
                      backing: .buffered,
                      defer: false)
window.delegate = WindowDelegate()

class WindowDelegate: NSObject, NSWindowDelegate {
    func windowDidBecomeKey(_ notification: Notification) {
        // 窗口获得焦点时的处理逻辑
    }
    
    func windowDidResignKey(_ notification: Notification) {
        // 窗口失去焦点时的处理逻辑
    }
}