如何在不重复代码的情况下在所有控制器中显示警报？

开发Swift你应该知道可以轻松解决问题的协议.您可以创建新协议MyAlert并为UIViewController类创建默认实现.然后只需MyAlert在视图控制器中继承您的协议,您需要它,并调用该函数!

protocol MyAlert {
    func runMyAlert()
}

extension MyAlert where Self: UIViewController {
    func runMyAlert() {
        let alert = UIAlertController(title: title, message: "message", preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction(UIAlertAction(title: "buttonTitle", style: UIAlertActionStyle.Default, handler: nil))
        self.presentViewController(alert, animated: true, completion: nil)
    }
}

所以你可以实现并调用它:

class MyViewController: UIViewController, MyAlert {
    override func viewDidLoad() {
        runMyAlert() // for test
    }
}

UPD:

您案件的代码:

protocol MyAlert {
    func runMyAlert()
}

extension MyAlert where Self: UIViewController {
    func runMyAlert() {
        let alert = UIAlertController(title: title, message: "message", preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction(UIAlertAction(title: "buttonTitle", style: UIAlertActionStyle.Default, handler: nil))
        self.presentViewController(alert, animated: true, completion: nil)
    }
}

class OpenChatsTableViewController: UITableViewController, MyAlert, OneRosterDelegate, BuddyRequestProtocol {
    override func viewDidLoad() {
        runMyAlert()
    }
}