1. 清除字符串小数点末尾的0

代码

import UIKit

extension String {
    /// 清除字符串小数点末尾的0
    func cleanDecimalPointZear() -> String {
        let newStr = self as NSString
        var s = NSString()
        
        var offset = newStr.length - 1
        while offset > 0 {
            s = newStr.substringWithRange(NSMakeRange(offset, 1))
            if s.isEqualToString("0") || s.isEqualToString(".") {
               offset -= 1
            } else {
                break
            }
        }
        return newStr.substringToIndex(offset + 1)
    }
}

2. 计算字符串的高度

主要通过以下两个方法计算：
// String
func boundingRectWithSize(size: CGSize, options: NSStringDrawingOptions, attributes: [NSObject : AnyObject]!, context: NSStringDrawingContext!) -> CGRect
第一个参数是传入一个CGSize结构体;
第二个参数options是个配置选项
高度计算时就传入NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading
如果你是用的String 的方法就有第三个参数：attributes其实就是NSAttributeString的属性，是个字典类型的对象，传入你的字体
let attrs = [NSFontAttributeName : UIFont.systemFontOfSize(14)]
最后一个参数就穿nil 就好了
// 例子
let rowHeight: CGFloat = str.boundingRectWithSize(maxSize, options: NSStringDrawingOptions.UsesLineFragmentOrigin, attributes: [NSFontAttributeName : UIFont.systemFontOfSize(14)], context: nil).size.height + 14

// NSAttributedString
func boundingRectWithSize(size: CGSize, options: NSStringDrawingOptions, context: NSStringDrawingContext?) -> CGRect
注意：如果是计算NSMutableAttributedString，必须设置富文本的字体样式，才可以计算正确

代码

extension String {
    func heightWithConstrainedWidth(width: CGFloat, font: UIFont) -> CGFloat {
        let constraintRect = CGSize(width: width, height: CGFloat.max)
        let boundingBox = self.boundingRectWithSize(constraintRect, options: NSStringDrawingOptions.UsesLineFragmentOrigin, attributes: [NSFontAttributeName: font], context: nil)
        return boundingBox.height
    }
}

extension NSAttributedString {
func heightWithConstrainedWidth(width: CGFloat) -> CGFloat {
    let constraintRect = CGSize(width: width, height: CGFloat.max)
    let boundingBox = self.boundingRectWithSize(constraintRect, options: NSStringDrawingOptions.UsesLineFragmentOrigin, context: nil)
    return ceil(boundingBox.height)
  }
}