public static class XmlSerializer
{
  public static void SaveToXml(string filePath, object sourceObj, Type type, string xmlRootName)
  {
    if (!string.IsNullOrWhiteSpace(filePath) && sourceObj != null)
    {
      type = type != null ? type : sourceObj.GetType();
      using (StreamWriter writer = new StreamWriter(filePath))
      {
        System.Xml.Serialization.XmlSerializer xmlSerializer = string.IsNullOrWhiteSpace(xmlRootName) ?
          new System.Xml.Serialization.XmlSerializer(type) :
          new System.Xml.Serialization.XmlSerializer(type, new XmlRootAttribute(xmlRootName));
        xmlSerializer.Serialize(writer, sourceObj);
      }
    }
  }
  public static object LoadFromXml(string filePath, Type type)
  {
    object result = null;
    if (File.Exists(filePath))
    {
      using (StreamReader reader = new StreamReader(filePath))
      {
        System.Xml.Serialization.XmlSerializer xmlSerializer = new System.Xml.Serialization.XmlSerializer(type);
        result = xmlSerializer.Deserialize(reader);
      }
    }
    return result;
  }
}

[XmlRootAttribute("MyCity", Namespace="abc.abc", IsNullable=false)]   // 当该类为Xml根节点时，以此为根节点名称。
public class City
[XmlAttribute("AreaName")]  // 表现为Xml节点属性。<... AreaName="..."/>
public string Name
[XmlElementAttribute("AreaId", IsNullable = false)]  // 表现为Xml节点。<AreaId>...</AreaId>
public string Id
[XmlArrayAttribute("Areas")]  // 表现为Xml层次结构，根为Areas，其所属的每个该集合节点元素名为类名。<Areas><Area ... /><Area ... /></Areas>
public Area[] Areas
[XmlElementAttribute("Area", IsNullable = false)]  // 表现为水平结构的Xml节点。<Area ... /><Area ... />...
public Area[] Areas
[XmlIgnoreAttribute]  // 忽略该元素的序列化。

[XmlRootAttribute("MyCity", Namespace = "abc.abc", IsNullable = false)]
public class City
{
  [XmlAttribute("CityName")]
  public string Name
  {
    get;
    set;
  }
  [XmlAttribute("CityId")]
  public string Id
  {
    get;
    set;
  }
  [XmlArrayAttribute("Areas")]
  public Area[] Areas
  {
    get;
    set;
  }
}
[XmlRootAttribute("MyArea")]
public class Area
{
  [XmlAttribute("AreaName")]
  public string Name
  {
    get;
    set;
  }
  [XmlElementAttribute("AreaId", IsNullable = false)]
  public string Id
  {
    get;
    set;
  }
  [XmlElementAttribute("Street", IsNullable = false)]
  public string[] Streets
  {
    get;
    set;
  }
}

static void Main(string[] args)
{
  Area area1 = new Area();
  area1.Name = "Pudong";
  area1.Id = "PD001";
  area1.Streets = new string [] { "street 001", "street 002" };
  Area area2 = new Area();
  area2.Name = "Xuhui";
  area2.Id = "XH002";
  area2.Streets = new string [] { "street 003", "street 004" };
  City city1 = new City();
  city1.Name = "Shanghai";
  city1.Id = "SH001";
  city1.Areas = new Area[] { area1, area2 };
  XmlSerializer.SaveToXml(@"C:\temp\XML\output003.xml", city1);
}

<?xml version="1.0" encoding="utf-8"?>
<MyCity xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
CityName="Shanghai" CityId="SH001" xmlns="abc.abc">
 <Areas>
  <Area AreaName="Pudong">
   <AreaId>PD001</AreaId>
   <Street>street 001</Street>
   <Street>street 002</Street>
  </Area>
  <Area AreaName="Xuhui">
   <AreaId>XH002</AreaId>
   <Street>street 003</Street>
   <Street>street 004</Street>
  </Area>
 </Areas>
</MyCity>