//新增更改app.Config的值
private void OptConfig(string AppKey, string AppValue)
{
    try
    {
        Assembly Asm = Assembly.GetExecutingAssembly();
        XmlDocument xmlDoc = new XmlDocument();

        string m_strFullPath = Asm.Location.Substring(0, (Asm.Location.LastIndexOf("\\") + 1)) + "YourAppName.exe.config";
        xmlDoc.Load(m_strFullPath);

        XmlDocument xDoc = new XmlDocument();
        xDoc.Load(m_strFullPath);
        XmlNode xNode;
        XmlElement xElem1;
        XmlElement xElem2;
        xNode = xDoc.SelectSingleNode("//appSettings");
        xElem1 = (XmlElement) xNode.SelectSingleNode("//add[@key='" + AppKey + "']");
        if (xElem1 != null)
        {
            xElem1.SetAttribute("value", AppValue);
        }
        else
        {
            xElem2 = xDoc.CreateElement("add");
            xElem2.SetAttribute("key", AppKey);
            xElem2.SetAttribute("value", AppValue);
            xNode.AppendChild(xElem2);
        }
        xDoc.Save(m_strFullPath);
    }
    catch (System.NullReferenceException NullEx)
    {
        throw NullEx;
    }
    catch (Exception ex)
    {
        throw ex;
    }
}