如何在不同ViewController中同步静音/取消静音按钮的图片状态？

你当前的写法let controller = FirstVC()是创建了一个全新的FirstController实例，和界面上正在显示的实例完全无关，所以调用changeButton()不会对原页面的按钮产生任何效果。下面提供三种可行的实现方式：

适合简单的父子VC通信，逻辑清晰直接。

1. 修改SecondController，添加闭包属性：

class SecondController: UIViewController {
    var index: Int = 0
    // 定义闭包，用于传递静音状态变化
    var muteStateChanged: ((Bool) -> Void)?
    
    // 静音按钮点击事件
    @IBAction func muteButtonTapped(_ sender: UIButton) {
        // 切换当前按钮图片
        let isMuted = sender.imageView?.image == UIImage(named: "unmute")
        sender.setImage(isMuted ? UIImage(named: "mute") : UIImage(named: "unmute"), for: .normal)
        // 通过闭包把状态传递给FirstController
        muteStateChanged?(isMuted)
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
}

2. 在FirstController跳转时设置闭包：

class FirstController: UIViewController, UICollectionViewDelegate {
    // 假设这是你的静音按钮
    @IBOutlet weak var muteButton: UIButton!
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let detailController = SecondController()
        detailController.index = indexPath.row + 1
        detailController.modalPresentationStyle = .overFullScreen
        // 设置闭包，接收状态并更新自身按钮
        detailController.muteStateChanged = { [weak self] isMuted in
            self?.muteButton.setImage(isMuted ? UIImage(named: "mute") : UIImage(named: "unmute"), for: .normal)
        }
        self.present(detailController, animated: false)
    }
}

适合更复杂的VC通信场景，扩展性更强。

1. 定义代理协议：

// 定义代理协议，规范状态传递方法
protocol MuteStateDelegate: AnyObject {
    func muteStateDidChange(isMuted: Bool)
}

2. 修改SecondController添加代理属性：

class SecondController: UIViewController {
    var index: Int = 0
    // 代理对象需用weak避免循环引用
    weak var delegate: MuteStateDelegate?
    
    @IBAction func muteButtonTapped(_ sender: UIButton) {
        let isMuted = sender.imageView?.image == UIImage(named: "unmute")
        sender.setImage(isMuted ? UIImage(named: "mute") : UIImage(named: "unmute"), for: .normal)
        // 调用代理方法传递状态
        delegate?.muteStateDidChange(isMuted: isMuted)
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
}

3. 让FirstController遵守代理协议并实现方法：

class FirstController: UIViewController, UICollectionViewDelegate, MuteStateDelegate {
    @IBOutlet weak var muteButton: UIButton!
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let detailController = SecondController()
        detailController.index = indexPath.row + 1
        detailController.modalPresentationStyle = .overFullScreen
        // 设置代理
        detailController.delegate = self
        self.present(detailController, animated: false)
    }
    
    // 实现代理方法，更新按钮状态
    func muteStateDidChange(isMuted: Bool) {
        muteButton.setImage(isMuted ? UIImage(named: "mute") : UIImage(named: "unmute"), for: .normal)
    }
}

适合跨多层VC或非直接关联的VC通信，注意要及时移除通知避免内存泄漏。

1. 在SecondController中发送通知：

class SecondController: UIViewController {
    var index: Int = 0
    // 定义通知名称常量
    static let muteStateChangedNotification = Notification.Name("MuteStateChanged")
    
    @IBAction func muteButtonTapped(_ sender: UIButton) {
        let isMuted = sender.imageView?.image == UIImage(named: "unmute")
        sender.setImage(isMuted ? UIImage(named: "mute") : UIImage(named: "unmute"), for: .normal)
        // 发送通知，携带状态参数
        NotificationCenter.default.post(name: Self.muteStateChangedNotification, object: nil, userInfo: ["isMuted": isMuted])
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
}

2. 在FirstController中监听通知：

class FirstController: UIViewController, UICollectionViewDelegate {
    @IBOutlet weak var muteButton: UIButton!
    // 保存通知监听对象，用于后续移除
    var notificationObserver: NSObjectProtocol?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // 添加通知监听
        notificationObserver = NotificationCenter.default.addObserver(forName: SecondController.muteStateChangedNotification, object: nil, queue: .main) { [weak self] notification in
            if let isMuted = notification.userInfo?["isMuted"] as? Bool {
                self?.muteButton.setImage(isMuted ? UIImage(named: "mute") : UIImage(named: "unmute"), for: .normal)
            }
        }
    }
    
    // 页面销毁时移除通知监听
    deinit {
        if let observer = notificationObserver {
            NotificationCenter.default.removeObserver(observer)
        }
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let detailController = SecondController()
        detailController.index = indexPath.row + 1
        detailController.modalPresentationStyle = .overFullScreen
        self.present(detailController, animated: false)
    }
}

内容的提问来源于stack exchange，提问作者Alex Smith