swift alertcontroller添加view出错

这段代码出错了，添加alertVC.setValue(alertView, forKey: "FullintentViewController")的时候就会出现terminating with uncaught exception of type NSException的错误，是怎么回事呢

直接addSubview

 var alertController = UIAlertController(title: "\n\n\n\n\n\n", message: nil, preferredStyle: UIAlertControllerStyle.ActionSheet)

let margin:CGFloat = 8.0
let rect = CGRectMake(margin, margin, alertController.view.bounds.size.width - margin * 4.0, 100.0)
var customView = UIView(frame: rect)

customView.backgroundColor = UIColor.greenColor()
alertController.view.addSubview(customView)

let somethingAction = UIAlertAction(title: "Something", style: UIAlertActionStyle.Default, handler: {(alert: UIAlertAction!) in println("something")})

let cancelAction = UIAlertAction(title: "Cancel", style: UIAlertActionStyle.Cancel, handler: {(alert: UIAlertAction!) in println("cancel")})

alertController.addAction(somethingAction)
alertController.addAction(cancelAction)

self.presentViewController(alertController, animated: true, completion:{})

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