在C#中，使用XML序列化處理復雜對象主要涉及到以下幾個方面：

1. 定義復雜對象類：首先，你需要定義一個包含多個屬性和子對象的類。這些屬性和子對象可以是基本數據類型、枚舉、集合（如List或Array）或其他自定義類。

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public Address Address { get; set; }
    public List<string> Hobbies { get; set; }
}

public class Address
{
    public string Street { get; set; }
    public string City { get; set; }
    public string PostalCode { get; set; }
}

2. 添加XML序列化屬性：為了控制XML序列化過程中的元素名稱、命名空間等，你可以為類和屬性添加XmlElement、XmlAttribute、XmlRoot等特性。

[XmlRoot("Person")]
public class Person
{
    [XmlElement("Name")]
    public string Name { get; set; }
    [XmlElement("Age")]
    public int Age { get; set; }
    [XmlElement("Address")]
    public Address Address { get; set; }
    [XmlElement("Hobbies")]
    public List<string> Hobbies { get; set; }
}

[XmlRoot("Address")]
public class Address
{
    [XmlElement("Street")]
    public string Street { get; set; }
    [XmlElement("City")]
    public string City { get; set; }
    [XmlElement("PostalCode")]
    public string PostalCode { get; set; }
}

3. 序列化對象：使用XmlSerializer類將復雜對象序列化為XML字符串。

Person person = new Person
{
    Name = "John Doe",
    Age = 30,
    Address = new Address
    {
        Street = "123 Main St",
        City = "New York",
        PostalCode = "10001"
    },
    Hobbies = new List<string> { "Reading", "Traveling" }
};

XmlSerializer serializer = new XmlSerializer(typeof(Person));
StringWriter writer = new StringWriter();
serializer.Serialize(writer, person);
string xmlString = writer.ToString();

4. 反序列化XML：使用XmlSerializer類將XML字符串反序列化為復雜對象。

string xmlString =<Person><Name>John Doe</Name><Age>30</Age<Address><Street>123 Main St</Street><City>New York</City><PostalCode>10001</PostalCode></Address><Hobbies<string>Reading</string<string>Traveling</string></Hobbies></Person>";

XmlSerializer serializer = new XmlSerializer(typeof(Person));
StringReader reader = new StringReader(xmlString);
Person deserializedPerson = (Person)serializer.Deserialize(reader);

通過以上步驟，你可以實現復雜對象的XML序列化和反序列化。注意，在處理更復雜的對象時，可能需要處理繼承、抽象類、接口等高級概念。在這些情況下，你可能需要使用XmlInclude、XmlType等特性來指定相關類型。