判断XML文件是否存在，不存在就创建一个XMl文件，存在就在里面添加一条数据

因为学习 网上搜到的很好的源码 转来与大家分享

if (File.Exists(xmlPath + "//" + xmlName)) //判断文件是否寸在
{
//存在的情况下
XmlDocument xmldoc = new XmlDocument();
xmldoc.Load(xmlPath + "//" + xmlName);
//存在文件
XmlNode root = xmldoc.SelectSingleNode("History");
XmlElement bak = xmldoc.CreateElement("Bak");
root.AppendChild(bak);

XmlElement bakTime = xmldoc.CreateElement("BakTime");
bakTime.InnerText = DateTime.Now.ToString();
bak.AppendChild(bakTime); //备份时间

XmlElement bakName = xmldoc.CreateElement("BakName");
bakName.InnerText = dbFileName;
bak.AppendChild(bakName); // 备份的名字

XmlElement DataSource = xmldoc.CreateElement("DataSource");
DataSource.InnerText = dataSource;
bak.AppendChild(DataSource); //数据源

XmlElement Database = xmldoc.CreateElement("Database");
Database.InnerText = database;
bak.AppendChild(Database); //数据库名称

XmlElement DatabaseUser = xmldoc.CreateElement("UserID");
DatabaseUser.InnerText = userID;
bak.AppendChild(DatabaseUser); //数据库用户名

XmlElement Password = xmldoc.CreateElement("Password");
Password.InnerText = password;
bak.AppendChild(Password); // 数据库密码

XmlElement UserName = xmldoc.CreateElement("StaffName");
UserName.InnerText = staffName;
bak.AppendChild(UserName); //备份人

xmldoc.Save(xmlPath + "//" + xmlName);

}
else
{
//不存在文件
Directory.CreateDirectory(xmlPath);//创建该文件

XmlDocument xmldoc = new XmlDocument();

XmlNode xmlnode = xmldoc.CreateXmlDeclaration("1.0", "gb2312", null);
xmldoc.AppendChild(xmlnode);

XmlElement root = xmldoc.CreateElement("History");
xmldoc.AppendChild(root);
XmlElement bak = xmldoc.CreateElement("Bak");
root.AppendChild(bak);

XmlElement bakTime = xmldoc.CreateElement("BakTime");
bakTime.InnerText = DateTime.Now.ToString();
bak.AppendChild(bakTime); //备份时间

XmlElement bakName = xmldoc.CreateElement("BakName");
bakName.InnerText = dbFileName;
bak.AppendChild(bakName); // 备份的名字

XmlElement DataSource = xmldoc.CreateElement("DataSource");
DataSource.InnerText = dataSource;
bak.AppendChild(DataSource); //数据源

XmlElement Database = xmldoc.CreateElement("Database");
Database.InnerText = database;
bak.AppendChild(Database); //数据库

XmlElement DatabaseUser = xmldoc.CreateElement("UserID");
DatabaseUser.InnerText = userID;
bak.AppendChild(DatabaseUser); //数据库用户名

XmlElement Password = xmldoc.CreateElement("Password");
Password.InnerText = password;
bak.AppendChild(Password); // 数据库密码

XmlElement UserName = xmldoc.CreateElement("StaffName");
UserName.InnerText = staffName;
bak.AppendChild(UserName); //备份人

xmldoc.Save(xmlPath + "//" + xmlName);
}