UIAlertControlle时IOS的对话框控制器（警报控制器），简单使用方法如下：
步骤都一样，先是创建UIAlertController，然后创建UIAlertAction，再将UIAlertAction添加到UIAlertController中，最后显示对话框。

文本对话框：

		//创建控制器
        let alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)
        //设置action
        let okAction = UIAlertAction(title: "OK", style: .default){
            (action) in
            print("click OK")
        }
        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
        //添加action
        alertController.addAction(okAction)
        alertController.addAction(cancelAction)
        //显示对话框
        present(alertController, animated: true, completion: nil)

效果如图：

带输入框的对话框

		//创建控制器
        let alertController = UIAlertController(title: "Enter Text", message: nil, preferredStyle: .alert)
        //设置输入框
        alertController.addTextField { (textField) in
            textField.placeholder = "Enter text"
        }
        //设置action
        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
        let submitAction = UIAlertAction(title: "Submit", style: .default) { (action) in
            if let text = alertController.textFields?.first?.text {
                print("Entered text: \(text)")
            }
        }
        //添加action
        alertController.addAction(cancelAction)
        alertController.addAction(submitAction)
        //显示对话框
        present(alertController, animated: true, completion: nil)

效果如图：

底部选择对话框

注意preferredStyle为.actionSheet

		//创建控制器
        let alertController = UIAlertController(title: "Choose Option", message: nil, preferredStyle: .actionSheet)
        //设置action
        let option1Action = UIAlertAction(title: "Option 1", style: .default) { (action) in
            print("Option 1 selected")
        }
        let option2Action = UIAlertAction(title: "Option 2", style: .default) { (action) in
            print("Option 2 selected")
        }
        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
        //添加action
        alertController.addAction(option1Action)
        alertController.addAction(option2Action)
        alertController.addAction(cancelAction)
        //显示对话框
        present(alertController, animated: true, completion: nil)

效果如图：