A function for showing alerts and action sheets, written for iOS 7 and 8

showAlert.swift

import UIKit

// Notes:
// - You must explicitly weak link to UIKit to support iOS 7
// - Action sheets on iOS 7 only show a title

func showAlert(viewController: UIViewController, style: UIAlertControllerStyle = .Alert, title: String? = nil, message: String? = nil, sourceView: UIView? = nil, completion: (() -> ())? = nil, buttons: (UIAlertActionStyle, String, (() -> ())?)...) {
    
    if (NSClassFromString("UIAlertController") != nil) {
        // iOS 8+
        let alertController = UIAlertController(title: title, message: message, preferredStyle: style)
        for button in buttons {
            alertController.addAction(UIAlertAction(title: button.1, style: button.0) { (_: UIAlertAction!) in
                if let completion = completion { completion() }
                if let cb = button.2 { cb() }
            })
        }
        if let sourceView = sourceView {
            if let popoverPresentationController = alertController.popoverPresentationController {
                popoverPresentationController.sourceView = sourceView
                popoverPresentationController.sourceRect = sourceView.bounds
            }
        }
        
        viewController.presentViewController(alertController, animated: true, completion: nil)
        
    } else {
        // iOS 7
        class Helper: NSObject {
            
            var holdSelf: Helper?
            var cb: (Int) -> ()
            
            init(cb: (Int) -> ()) {
                self.cb = cb
                super.init()
                self.holdSelf = self
            }
            
            func finish(index: Int) {
                self.cb(index)
                self.holdSelf = nil
            }
        }

        switch style {
        case .ActionSheet:
            class ActionSheetHelper : Helper, UIActionSheetDelegate {
                init(_ actionSheet: UIActionSheet, cb: (Int) -> ()) {
                    super.init(cb: cb)
                    actionSheet.delegate = self
                    
                }
                func actionSheet(actionSheet: UIActionSheet!, clickedButtonAtIndex buttonIndex: Int) {
                    actionSheet.delegate = nil
                    self.finish(buttonIndex)
                }
            }
            let actionSheet = UIActionSheet()
            if let title = title {
                actionSheet.title = title
            }
            for button in buttons {
                actionSheet.addButtonWithTitle(button.1)
                switch button.0 {
                case .Default:
                    break
                case .Cancel:
                    actionSheet.cancelButtonIndex = actionSheet.numberOfButtons - 1
                case .Destructive:
                    actionSheet.destructiveButtonIndex = actionSheet.numberOfButtons - 1
                }
            }
            ActionSheetHelper(actionSheet) {
                if let completion = completion { completion() }
                if let cb = buttons[$0].2 { cb() }
            }
            if let sourceView = sourceView {
                actionSheet.showFromRect(sourceView.bounds, inView: sourceView, animated: true)
            } else {
                actionSheet.showInView(viewController.view)
            }
        case .Alert:
            class AlertHelper : Helper, UIAlertViewDelegate {
                init(_ alertView: UIAlertView, cb: (Int) -> ()) {
                    super.init(cb: cb)
                    alertView.delegate = self
                    
                }
                func alertView(alertView: UIAlertView!, clickedButtonAtIndex buttonIndex: Int) {
                    alertView.delegate = nil
                    self.finish(buttonIndex)
                }
            }
            let alertView = UIAlertView()
            if let title = title {
                alertView.title = title
            }
            if let message = message {
                alertView.message = message
            }
            for button in buttons {
                alertView.addButtonWithTitle(button.1)
                switch button.0 {
                case .Cancel:
                    alertView.cancelButtonIndex = alertView.numberOfButtons - 1
                default:
                    break
                }
            }
            AlertHelper(alertView) {
                if let completion = completion { completion() }
                if let cb = buttons[$0].2 { cb() }
            }
            alertView.show()
        }
        
    }
}

How to use this?

how yo use this?