XML中特殊字符转义

/// <summary>
/// 特殊字符转义
/// </summary>
/// <param name="xml"></param>
/// <returns></returns>
public string XmlCharacterEscaping(string xml)
{
    string xmlNew = xml;
    if (xml.IndexOf("&") != -1)
    {
        xmlNew = xml.Replace("&", "&amp;");
    }
    if (xml.IndexOf("<") != -1)
    {
        xmlNew = xml.Replace("<", "&lt;");
    }
    if (xml.IndexOf(">") != -1)
    {
        xmlNew = xml.Replace(">", "&gt;");
    }
    if (xml.IndexOf('"') != -1)
    {
        char c = '"';
        xmlNew = xml.Replace(c.ToString(), "&quot;");
    }
    return xmlNew;
}