假設今天有個Person的類別如下。除了名字、年齡、性別外，內含_friends清單用以提供IsFriend與AddFriend函式所須用到的朋友清單資料。
VB.NET
Public Class Person
#Region “Enum” Enum SexType Boy Girl End Enum #End Region
#Region “Var” Private _name As String Private _year As Integer Private _sex As SexType Private _friendNames As New List(Of String) #End Region
#Region “Property” Public Property Name() As String Get If String.IsNullOrEmpty(_name) Then Return String.Empty End If Return _name End Get Set(ByVal value As String) _ End Set End Property
Public Property Year() As Integer Get Return _year End Get Set(ByVal value As Integer) _year = value End Set End Property
Public Property Sex() As SexType Get Return _sex End Get Set(ByVal value As SexType) _sex = value End Set End Property #End Region
#Region “Public Method” Public Sub AddFriend(ByVal people As Person) _friendNames.Add(people.Name) End Sub
Public Function IsFriend(ByVal people As Person) As Boolean For Each friendName As String In _friendNames If friend Then Return True End If Next Return False End Function #End Region
End Class
C#
public class Person {
#region Enum public enum SexType { Boy, Girl } #endregion
#region Var private string _name; private int _year; private SexType _sex; private List _friendNames = new List(); #endregion
#region Property public string Name { get { if (string.IsNullOrEmpty(_name)) { return string.Empty; } return _name; } set { _ } }
public int Year { get { return _year; } set { _year = value; } }
public SexType Sex { get { return _sex; } set { _sex = value; } } #endregion
#region Public Method public void AddFriend(Person people) { _friendNames.Add(people.Name); }
public bool IsFriend(Person people) { foreach (String friendName in _friendNames) { if (friend people.Name) { return true; } } return false; } #endregion
}
在.NET程式裡，若將該類別直接做XML序列化，則其類別的_friends這個私有的欄位資料將不會被序列化保存 (因為.NET XML序列化無法序列化私有欄位資料)。此時我們可以用自定義XML的方式來去解決此問題。透過自定義XML序列化，我們可以自己定義XML序列化的格式。也可以把本來不會序列化的私有欄位一併序列化。
但是，若只是很單純的去實作自定義XML序列化。做出來的類別將無法與.NET本身的XML序列化做整合。舉個例子來說，假設今天Person這個類別實作了自定義XML序列化。而程式中又有個PersonCollection這個類別內含Person這個類別成員。則此時，若PersonCollection這個類別沒有實作自定義XML序列化，而想直接用來序列化的話。該程式在序列化時將會發生錯誤。也就是說，當A這個類別做了自定義XML序列化，而B這個類別的成員內含A這個類別時，則B通常也將需要自定義XML序列化。
要解決該問題，照著下面程式碼片段的格式去實作自定義XML序列化即可。
VB.NET
#Region “Implement IXmlSerializable” Public Function GetSchema() As System.Xml.Schema.XmlSchema Implements System.Xml.Serialization.IXmlSerializable.GetSchema Return Nothing End Function
Public Sub ReadXml(ByVal reader As System.Xml.XmlReader) Implements System.Xml.Serialization.IXmlSerializable.ReadXml Dim startElementName As String = reader.Name Dim currentElementName As String
Me._friendNames.Clear() Do currentElement If currentElement AndAlso (reader.MoveToContent = Xml.XmlNodeType.EndElement OrElse reader.IsEmptyElement) Then reader.Read() Exit Do End If
Select Case currentElementName Case “Name” Me.
Case “Sex” Me.Sex = CType(reader.ReadElementString(), SexType)
Case “Year” Me.Year = CInt(reader.ReadElementString())
Case “Friend” Me._friendNames.Add(reader.GetAttribute(“Name”)) reader.Read() Case Else reader.Read()
End Select
Loop End Sub
Public Sub WriteXml(ByVal writer As System.Xml.XmlWriter) Implements System.Xml.Serialization.IXmlSerializable.WriteXml writer.WriteElementString(“Name”, Name) writer.WriteElementString(“Sex”, CInt(Sex).ToString) writer.WriteElementString(“Year”, Year.ToString) For Each friendName As String In _friendNames writer.WriteStartElement(“Friend”) writer.WriteAttributeString(“Name”, friendName) writer.WriteEndElement() Next End Sub #End Region
C#
#region Implement IXmlSerializable
public System.Xml.Schema.XmlSchema GetSchema() { throw new NotImplementedException(); }
public void ReadXml(System.Xml.XmlReader reader) { string startElement string currentElementName;
this._friendNames.Clear(); do { currentElement if (currentElement startElementName && (reader.MoveToContent() == System.Xml.XmlNodeType.EndElement || reader.IsEmptyElement)) { reader.Read(); break; }
switch (currentElementName) { case “Name”: this. break;
case “Sex”: this.Sex = (SexType)int.Parse (reader.ReadElementString()); break;
case “Year”: this.Year = int.Parse(reader.ReadElementString()); break;
case “Friend”: this._friendNames.Add(reader.GetAttribute(“Name”)); reader.Read(); break; default: reader.Read(); break;
} }while (true); }
public void WriteXml(System.Xml.XmlWriter writer) { writer.WriteElementString(“Name”, Name); writer.WriteElementString(“Sex”, ((int)Sex).ToString()); writer.WriteElementString(“Year”, Year.ToString()); foreach (string friendName in _friendNames) { writer.WriteStartElement(“Friend”); writer.WriteAttributeString(“Name”, friendName); writer.WriteEndElement(); } }
#endregion
其主要重點概念如下圖所示：