public class Test
{
    private InnerTest innerTest;
    private int testNumber;


    public Test()
    {
        this.innerTest = new InnerTest();
        this.testNumber = 5;
    }


    public int TestNumber1
    {
        get { return this.testNumber; }
        set { this.testNumber = value;}
    }


    public InnerTest InnerTest
    {
        get { return this.innerTest; }
        set { this.innerTest = value;}
    }


}


public struct InnerTest
{
    private int number;


    public InnerTest(int number)
    {
        this.number = number;
    }
    public int Number{get { return number; }}
}

[DataMember]
public int TestNumber1
{
    get { return this.testNumber; }
    set { this.testNumber = value;}
}

// note **not** a data-member
public InnerTest InnerTest
{
    get { return this.innerTest; }
    set { this.innerTest = value;}
}

[DataMember]
private int InnerTestValue
{
    get {return innerTest.Number;}
    set {innerTest = new InnerTest(value);}
}

Test test = new Test { TestNumber1 = 5 };

XmlSerializer xmlSer = new XmlSerializer(typeof(Test));
MemoryStream memStm = new MemoryStream();

xmlSer.Serialize(memStm, test);

StreamReader stmR = new StreamReader(memStm);
memStm.Position = 0;
string output = stmR.ReadToEnd();