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我想向 UIAlertController 添加图像。图像不需要在按钮上，只需呈现在 Controller 中间即可。我的代码在下面，但崩溃并显示消息“无法识别的选择器已发送到实例”。
func showAlert () {
let alert = UIAlertController(title: "Title of Alert",
message: "none",
preferredStyle:UIAlertControllerStyle.ActionSheet)
// add an image
let image = UIImage(named: "example")
var imageView = UIImageView(image: image)
imageView.frame = CGRectMake(0, 0, 100, 100)
var imageAction = UIAlertAction(title: "", style:.Default, handler: nil)
imageAction.setValue(imageView, forKey: "image")
alert.addAction(imageAction)
// add a continue button
var action = UIAlertAction(title: "Continue", style:.Default, handler: {(alert:UIAlertAction!) in self.continue() })
alert.addAction(action)
// show the UIAlertController
self.presentViewController(alert, animated: true, completion: nil)
}