如何修复iOS 15中'windows'被弃用问题（UIKit邮件控制器场景）

修复后的完整代码 #

private func presentMailCompose() {
    guard MFMailComposeViewController.canSendMail() else {
        return
    }
    
    // 替换弃用的windows API，适配iOS15+
    let rootViewController: UIViewController? = {
        // 获取当前激活的UIWindowScene
        guard let scene = UIApplication.shared.connectedScenes
                .filter({ $0.activationState == .foregroundActive })
                .first as? UIWindowScene else {
            return nil
        }
        // 获取场景的keyWindow，再取rootViewController
        return scene.windows.filter({ $0.isKeyWindow }).first?.rootViewController
    }()
    
    let composeVC = MFMailComposeViewController()
    composeVC.mailComposeDelegate = mailComposeDelegate
    
    // 自定义邮件内容示例（可选）
    composeVC.setToRecipients(["example@domain.com"])
    composeVC.setSubject("邮件主题")
    composeVC.setMessageBody("邮件内容", isHTML: false)
    
    rootViewController?.present(composeVC, animated: true)
}

关键修复点说明 #

• 替换弃用API：用UIApplication.shared.connectedScenes替代UIApplication.shared.windows，这是iOS15官方推荐的多场景适配方案
• 筛选激活场景：通过activationState == .foregroundActive确保拿到当前用户正在交互的场景，避免多窗口场景下的错误
• 安全获取根控制器：通过可选绑定和过滤，避免因为场景或窗口不存在导致的崩溃

更优写法（如果在ViewController内部调用） #

如果这个方法是在某个UIViewController子类中实现的，无需全局查找根控制器，直接用当前控制器present更简洁：

private func presentMailCompose() {
    guard MFMailComposeViewController.canSendMail() else {
        return
    }
    
    let composeVC = MFMailComposeViewController()
    composeVC.mailComposeDelegate = mailComposeDelegate
    
    // 自定义邮件内容
    composeVC.setToRecipients(["example@domain.com"])
    
    present(composeVC, animated: true)
}

补充：邮件代理实现（避免内存泄漏） #

别忘了实现MFMailComposeViewControllerDelegate，确保邮件界面关闭后正确释放资源：

extension YourClass: MFMailComposeViewControllerDelegate {
    func mailComposeController(_ controller: MFMailComposeViewController, didFinishWith result: MFMailComposeResult, error: Error?) {
        controller.dismiss(animated: true)
    }
}

内容的提问来源于stack exchange，提问作者jchan12345