swift 根据文字大小多少拉伸背景图

原理就是将图片四周拉伸,用中间部分进行填充

//4.根据文字内容确定大小
       
        let text:String = "今天成交量依然不能有效放有效放天成交量依然大，交量依然不能有效放天成交量依然不能有效放大，"
        let btnBgImage:UIImage = UIImage(named: "sign_bg_tieshi")!
        //        设置图片的拉伸方式
        let w: CGFloat = btnBgImage.size.width * 0.5
        let h: CGFloat = btnBgImage.size.height * 0.5
        let newImage:UIImage = btnBgImage.resizableImageWithCapInsets(UIEdgeInsetsMake(h, w, h, w), resizingMode: .Stretch)
        tipBtn.setBackgroundImage(newImage, forState: .Normal)
        tipBtn.setTitle(text, forState: .Normal)
//根据字体的大小文字的长度算出rect
        let texMaxSize: CGSize = CGSizeMake(220, CGFloat(MAXFLOAT))
        let textRect = TKOnlineTool.getTextRectSize(text, font: UIFont.systemFontOfSize(13), size: texMaxSize)
        let textHeight = textRect.size.height
        tipBtnHeight.constant = textHeight + 30

/**
     根据文字算出文字尺寸
     */
    class func getTextRectSize(text:NSString,font:UIFont,size:CGSize) -> CGRect {
        let attributes = [NSFontAttributeName: font]
        let option = NSStringDrawingOptions.UsesLineFragmentOrigin
        let rect:CGRect = text.boundingRectWithSize(size, options: option, attributes: attributes, context: nil)
        //        println("rect:\(rect)");
        return rect;
    }