这主要针对是 cell上label自适应高度，
let lineSpaceKey = "lineSpaceKey"
extension UILabel{
var lineSpace :CGFloat?{
set{
objc_setAssociatedObject(self, lineSpaceKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
get{
return (objc_getAssociatedObject(self, lineSpaceKey) as? CGFloat)
}
}
//label 内容行数 这的size 是label 的宽和高 lineSpace 是行间距
func textNumLinesWithHeight(size:CGSize) -> CGFloat {
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.lineBreakMode = self.lineBreakMode
paragraphStyle.alignment = self.textAlignment
if self.lineSpace == nil {
self.lineSpace = 0
}
paragraphStyle.lineSpacing = self.lineSpace!
let attributes = [NSFontAttributeName : self.font,
NSParagraphStyleAttributeName : paragraphStyle];
let contentSize = self.text!.boundingRectWithSize(size, options: [.UsesFontLeading,.UsesLineFragmentOrigin] , attributes: attributes, context: nil).size
let labelNumber = contentSize.height / self.font.lineHeight
return labelNumber
}
}