swift 动态计算UILabel的高度

extension UILabel{

//根据text的字体大小和控件的宽度以及字体内容动态计算label的高度

func getTheHeightForLabel(font:UIFont,width:CGFloat,text:String) ->UILabel{

let label =UILabel()

let textW = width

label.text= text

label.font= font

label.numberOfLines=0

let textAtt:NSDictionary= [NSFontAttributeName: font]

let textSize:CGSize=CGSizeMake(textW,CGFloat(MAXFLOAT))

let textH:CGFloat= label.text!.boundingRectWithSize(textSize,options: .UsesLineFragmentOrigin,attributes: textAttas? [String:AnyObject],context:nil).size.height

label.frame=CGRectMake(0,0, textW, textH)

return label

}