App.config 读、写

        /// <summary>
        /// 读
        /// </summary>
        /// <returns></returns>
        public string GetFolderPath() {
            FolderPath = ConfigurationSettings.AppSettings["folderPath"];
            return FolderPath;
        }

        /// <summary>
        /// 写
        /// </summary>
        public void SetFolderPath(string folderPath) {
            if (String.IsNullOrEmpty(folderPath)) return;

            string fullPath =@"E:\aa\App.config";
            if (!System.IO.File.Exists(fullPath)) {
                System.Windows.Forms.MessageBox.Show(fullPath + "文档不存在!");
                return;
            }
            XmlDocument doc = new XmlDocument();
            doc.Load(fullPath);
            XmlNodeList nodes = doc.GetElementsByTagName("add");
            for (int i = 0; i < nodes.Count; i++) {
                XmlAttribute att = nodes[i].Attributes["key"];
                if (att.Value == "folderPath") {
                    nodes[i].Attributes["value"].Value = folderPath;
                    break;
                }
            }
            doc.Save(fullPath);
        }