swift UILabel的高度自适应

let label = UILabel.init()
label.backgroundColor = UIColor.grayColor()
label.text = "1234567890-edfdgddffgfgfggfggddfbyfru6y6r7iuymgnjnrtfugyu57t6injyunjokn89uilmghbjl,hknjlllllllllllllllllllllllllllllllllllllmimomomkjnijunbuygbtyfrtdrxcresxweaswa"

label.font = UIFont.systemFontOfSize(14
)
label.textColor = UIColor.redColor()
let string:NSString = label.text!
let options:NSStringDrawingOptions = .UsesLineFragmentOrigin
let boundingRect = string.boundingRectWithSize(CGSizeMake(200, 0), options: options, attributes:[NSFontAttributeName:label.font], context: nil)
label.frame = CGRectMake(0, 20, 200, boundingRect.height)
label.numberOfLines = 0;
label.lineBreakMode = NSLineBreakMode.ByWordWrapping

self.view.addSubview(label)