UIActionSheet 这样写为什么显示为空白 ???

func pickePhotoFromSheet()

{

var sheet:UIActionSheet = UIActionSheet()

var  button = UIButton.buttonWithType(.Custom) as UIButton

button.frame  = CGRectMake(0,0,GETSCREENWIDTH,30)

button.backgroundColor = DefaultWhiteColor

button.setTitle("相册",forState:UIControlState.Normal)

button.setTitleColor(COLORWITHRGB(73,73,73), forState: UIControlState.Normal)

button.setImage(UIImage(named:"icon_album_normal.png"), forState: UIControlState.Normal)

button.setImage(UIImage(named:"icon_album_active.png"), forState: UIControlState.Highlighted)

//  button.addTarget(self,action:"photoChoose:",forControlEvents:UIControlEvents.TouchUpInside)

sheet.addSubview(button)

sheet.actionSheetStyle  =  UIActionSheetStyle.BlackOpaque

sheet.showInView(self.view)

}