방법: 파생 클래스의 serialization 제어

  • 아티클

XmlElementAttribute 특성을 사용하여 XML 요소의 이름을 변경하는 것이 개체 serialization을 사용자 지정하는 유일한 방법은 아닙니다. 기존 클래스에서 파생하고 새 클래스를 serialize하는 방법을 XmlSerializer 인스턴스에 지시하여 XML 스트림을 사용자 지정할 수도 있습니다.

예를 들어 Book 클래스의 경우 이 클래스에서 파생하고 몇 개의 속성이 더 있는 ExpandedBook 클래스를 만들 수 있습니다. 하지만 직렬화 또는 역직렬화할 때 파생된 형식을 허용하도록 XmlSerializer에 지시해야 합니다. 이렇게 하려면 XmlElementAttribute 인스턴스를 만들고 이 인스턴스의 Type 속성을 파생 클래스 형식으로 설정합니다. XmlElementAttribute를 XmlAttributes 인스턴스에 추가합니다. 그런 다음 XmlAttributes를 XmlAttributeOverrides 인스턴스로 추가하고 재정의되는 형식과 파생 클래스를 허용하는 멤버의 이름을 지정합니다. 이 방법은 다음 예제에서 확인할 수 있습니다.

예시

Public Class Orders  
    public Books() As Book  
End Class
  
Public Class Book  
    public ISBN As String
End Class  
  
Public Class ExpandedBook  
    Inherits Book  
    public NewEdition As Boolean  
End Class  
  
Public Class Run  
    Shared Sub Main()  
        Dim t As Run = New Run()  
        t.SerializeObject("Book.xml")  
        t.DeserializeObject("Book.xml")  
    End Sub  
  
    Public Sub SerializeObject(filename As String)  
        ' Each overridden field, property, or type requires
        ' an XmlAttributes instance.
        Dim attrs As XmlAttributes = New XmlAttributes()  
  
        ' Creates an XmlElementAttribute instance to override the
        ' field that returns Book objects. The overridden field  
        ' returns Expanded objects instead.  
        Dim attr As XmlElementAttribute = _  
        New XmlElementAttribute()  
        attr.ElementName = "NewBook"  
        attr.Type = GetType(ExpandedBook)  
  
        ' Adds the element to the collection of elements.  
        attrs.XmlElements.Add(attr)  
  
        ' Creates the XmlAttributeOverrides.  
        Dim attrOverrides As XmlAttributeOverrides = _  
        New XmlAttributeOverrides()  
  
        ' Adds the type of the class that contains the overridden
        ' member, as well as the XmlAttributes instance to override it
        ' with, to the XmlAttributeOverrides instance.
        attrOverrides.Add(GetType(Orders), "Books", attrs)  
  
        ' Creates the XmlSerializer using the XmlAttributeOverrides.  
        Dim s As XmlSerializer  = _  
        New XmlSerializer(GetType(Orders), attrOverrides)  
  
        ' Writing the file requires a TextWriter instance.  
        Dim writer As TextWriter = New StreamWriter(filename)  
  
        ' Creates the object to be serialized.  
        Dim myOrders As Orders = New Orders()  
  
        ' Creates an object of the derived type.  
        Dim b As ExpandedBook = New ExpandedBook()  
        b.ISBN= "123456789"  
        b.NewEdition = True  
        myOrders.Books = New ExpandedBook(){b}  
  
        ' Serializes the object.  
        s.Serialize(writer,myOrders)  
        writer.Close()  
    End Sub  
  
    Public Sub DeserializeObject(filename As String)  
        Dim attrOverrides As XmlAttributeOverrides = _  
        New XmlAttributeOverrides()  
        Dim attrs As XmlAttributes = New XmlAttributes()  
  
        ' Creates an XmlElementAttribute to override the
        ' field that returns Book objects. The overridden field  
        ' returns Expanded objects instead.
        Dim attr As XmlElementAttribute = _  
        New XmlElementAttribute()  
        attr.ElementName = "NewBook"  
        attr.Type = GetType(ExpandedBook)  
  
        ' Adds the XmlElementAttribute to the collection of objects.  
        attrs.XmlElements.Add(attr)  
  
        attrOverrides.Add(GetType(Orders), "Books", attrs)  
  
        ' Creates the XmlSerializer using the XmlAttributeOverrides.  
        Dim s As XmlSerializer = _  
        New XmlSerializer(GetType(Orders), attrOverrides)  
  
        Dim fs As FileStream = New FileStream(filename, FileMode.Open)  
        Dim myOrders As Orders = CType( s.Deserialize(fs), Orders)  
        Console.WriteLine("ExpandedBook:")  
  
        ' The difference between deserializing the overridden
        ' XML document and serializing it is this: To read the derived
        ' object values, you must declare an object of the derived type
        ' and cast the returned object to it.
        Dim expanded As ExpandedBook
        Dim b As Book  
        for each b  in myOrders.Books  
            expanded = CType(b, ExpandedBook)  
            Console.WriteLine(expanded.ISBN)  
            Console.WriteLine(expanded.NewEdition)  
        Next  
    End Sub  
End Class  

public class Orders  
{  
    public Book[] Books;  
}
  
public class Book  
{  
    public string ISBN;  
}  
  
public class ExpandedBook:Book  
{  
    public bool NewEdition;  
}  
  
public class Run  
{  
    public void SerializeObject(string filename)  
    {  
        // Each overridden field, property, or type requires
        // an XmlAttributes instance.  
        XmlAttributes attrs = new XmlAttributes();  
  
        // Creates an XmlElementAttribute instance to override the
        // field that returns Book objects. The overridden field  
        // returns Expanded objects instead.  
        XmlElementAttribute attr = new XmlElementAttribute();  
        attr.ElementName = "NewBook";  
        attr.Type = typeof(ExpandedBook);  
  
        // Adds the element to the collection of elements.  
        attrs.XmlElements.Add(attr);  
  
        // Creates the XmlAttributeOverrides instance.  
        XmlAttributeOverrides attrOverrides = new XmlAttributeOverrides();  
  
        // Adds the type of the class that contains the overridden
        // member, as well as the XmlAttributes instance to override it
        // with, to the XmlAttributeOverrides.  
        attrOverrides.Add(typeof(Orders), "Books", attrs);  
  
        // Creates the XmlSerializer using the XmlAttributeOverrides.  
        XmlSerializer s =
        new XmlSerializer(typeof(Orders), attrOverrides);  
  
        // Writing the file requires a TextWriter instance.  
        TextWriter writer = new StreamWriter(filename);  
  
        // Creates the object to be serialized.  
        Orders myOrders = new Orders();  
  
        // Creates an object of the derived type.  
        ExpandedBook b = new ExpandedBook();  
        b.ISBN= "123456789";  
        b.NewEdition = true;  
        myOrders.Books = new ExpandedBook[]{b};  
  
        // Serializes the object.  
        s.Serialize(writer,myOrders);  
        writer.Close();  
    }  
  
    public void DeserializeObject(string filename)  
    {  
        XmlAttributeOverrides attrOverrides =
            new XmlAttributeOverrides();  
        XmlAttributes attrs = new XmlAttributes();  
  
        // Creates an XmlElementAttribute to override the
        // field that returns Book objects. The overridden field  
        // returns Expanded objects instead.  
        XmlElementAttribute attr = new XmlElementAttribute();  
        attr.ElementName = "NewBook";  
        attr.Type = typeof(ExpandedBook);  
  
        // Adds the XmlElementAttribute to the collection of objects.  
        attrs.XmlElements.Add(attr);  
  
        attrOverrides.Add(typeof(Orders), "Books", attrs);  
  
        // Creates the XmlSerializer using the XmlAttributeOverrides.  
        XmlSerializer s =
        new XmlSerializer(typeof(Orders), attrOverrides);  
  
        FileStream fs = new FileStream(filename, FileMode.Open);  
        Orders myOrders = (Orders) s.Deserialize(fs);  
        Console.WriteLine("ExpandedBook:");  
  
        // The difference between deserializing the overridden
        // XML document and serializing it is this: To read the derived
        // object values, you must declare an object of the derived type
        // and cast the returned object to it.  
        ExpandedBook expanded;  
        foreach(Book b in myOrders.Books)
        {  
            expanded = (ExpandedBook)b;  
            Console.WriteLine(  
            expanded.ISBN + "\n" +
            expanded.NewEdition);  
        }  
    }  
}

참고 항목