XmlElementAttribute Class

Definition

Namespace:

System.Xml.Serialization

Assemblies:

netstandard.dll, System.Xml.ReaderWriter.dll

Source:

XmlElementAttribute.cs

Indicates that a public field or property represents an XML element when the XmlSerializer serializes or deserializes the object that contains it.

C#

[System.AttributeUsage(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property | System.AttributeTargets.ReturnValue, AllowMultiple=true)]
public class XmlElementAttribute : Attribute

Inheritance

Object

Attribute

XmlElementAttribute

Attributes

AttributeUsageAttribute

Examples

The following example serializes a class named Group and applies the XmlElementAttribute to several of its members. The field named Employees returns an array of Employee objects. In this case, the XmlElementAttribute specifies that the resulting XML will not be nested (which is the default behavior of items in an array).

C#

using System;
using System.Collections;
using System.IO;
using System.Xml.Serialization;

public class Group
{
   /* Set the element name and namespace of the XML element.
   By applying an XmlElementAttribute to an array,  you instruct
   the XmlSerializer to serialize the array as a series of XML
   elements, instead of a nested set of elements. */

   [XmlElement(
   ElementName = "Members",
   Namespace = "http://www.cpandl.com")]
   public Employee[] Employees;

   [XmlElement(DataType = "double",
   ElementName = "Building")]
   public double GroupID;

   [XmlElement(DataType = "hexBinary")]
   public byte [] HexBytes;

   [XmlElement(DataType = "boolean")]
   public bool IsActive;

   [XmlElement(Type = typeof(Manager))]
   public Employee Manager;

   [XmlElement(typeof(int),
   ElementName = "ObjectNumber"),
   XmlElement(typeof(string),
   ElementName = "ObjectString")]
   public ArrayList ExtraInfo;
}

public class Employee
{
   public string Name;
}

public class Manager:Employee{
   public int Level;
}

public class Run
{
    public static void Main()
    {
       Run test = new Run();
       test.SerializeObject("FirstDoc.xml");
       test.DeserializeObject("FirstDoc.xml");
    }

   public void SerializeObject(string filename)
   {
      // Create the XmlSerializer.
      XmlSerializer s = new XmlSerializer(typeof(Group));

      // To write the file, a TextWriter is required.
      TextWriter writer = new StreamWriter(filename);

      /* Create an instance of the group to serialize, and set
         its properties. */
      Group group = new Group();
      group.GroupID = 10.089f;
      group.IsActive = false;

      group.HexBytes = new byte[1]{Convert.ToByte(100)};

      Employee x = new Employee();
      Employee y = new Employee();

      x.Name = "Jack";
      y.Name = "Jill";

      group.Employees = new Employee[2]{x,y};

      Manager mgr = new Manager();
      mgr.Name = "Sara";
      mgr.Level = 4;
      group.Manager = mgr;

      /* Add a number and a string to the
      ArrayList returned by the ExtraInfo property. */
      group.ExtraInfo = new ArrayList();
      group.ExtraInfo.Add(42);
      group.ExtraInfo.Add("Answer");

      // Serialize the object, and close the TextWriter.
      s.Serialize(writer, group);
      writer.Close();
   }

   public void DeserializeObject(string filename)
   {
      FileStream fs = new FileStream(filename, FileMode.Open);
      XmlSerializer x = new XmlSerializer(typeof(Group));
      Group g = (Group) x.Deserialize(fs);
      Console.WriteLine(g.Manager.Name);
      Console.WriteLine(g.GroupID);
      Console.WriteLine(g.HexBytes[0]);
      foreach(Employee e in g.Employees)
      {
         Console.WriteLine(e.Name);
      }
   }
}

Remarks

The XmlElementAttribute belongs to a family of attributes that controls how the XmlSerializer serializes or deserializes an object. For a complete list of similar attributes, see Attributes That Control XML Serialization.

An XML document usually contains XML elements, each of which consists of three parts: an opening tag with possible attributes, a closing tag, and the data between the tags. XML tags can be nested--that is, the data between tags can also be XML elements. This capacity of one element to enclose another allows the document to contain hierarchies of data. An XML element can also include attributes.

Apply the XmlElementAttribute to public fields or public read/write properties to control characteristics of the XML elements such as the element name and namespace.

The XmlElementAttribute can be applied multiple times to a field that returns an array of objects. The purpose of this is to specify (through the Type property) different types that can be inserted into the array. For example, the array in the following C# code accepts both strings and integers.

public class Things{  
   [XmlElement(Type = typeof(string)),  
   XmlElement(Type = typeof(int))]  
   public object[] StringsAndInts;  
}  

This results in XML that might resemble the following.

<Things>  
   <string>Hello</string>  
   <int>999</int>  
   <string>World</string>  
</Things>  

Note that when you apply the XmlElementAttribute multiple times without specifying an ElementName property value, the elements are named after the type of the acceptable objects.

If you apply the XmlElementAttribute to a field or property that returns an array, the items in the array are encoded as a sequence of XML elements.

In contrast if an XmlElementAttribute is not applied to such a field or property, the items in the array are encoded as a sequence of elements, nested under an element named after the field or property. (Use the XmlArrayAttribute and XmlArrayItemAttribute attributes to control how an array is serialized.)

You can set the Type property to specify a type that is derived from the type of the original field or property--that is, the field or property to which you have applied the XmlElementAttribute.

If a field or property returns an ArrayList, you can apply multiple instances of the XmlElementAttribute to the member. For each instance, set the Type property to a type of object that can be inserted into the array.

For more information about using attributes, see Attributes.

Примітка

You can use the word XmlElement in your code instead of the longer XmlElementAttribute.

Constructors

XmlElementAttribute()	Initializes a new instance of the XmlElementAttribute class.
XmlElementAttribute(String, Type)	Initializes a new instance of the XmlElementAttribute and specifies the name of the XML element and a derived type for the member to which the XmlElementAttribute is applied. This member type is used when the XmlSerializer serializes the object that contains it.
XmlElementAttribute(String)	Initializes a new instance of the XmlElementAttribute class and specifies the name of the XML element.
XmlElementAttribute(Type)	Initializes a new instance of the XmlElementAttribute class and specifies a type for the member to which the XmlElementAttribute is applied. This type is used by the XmlSerializer when serializing or deserializing object that contains it.

Properties

DataType	Gets or sets the XML Schema definition (XSD) data type of the XML element generated by the XmlSerializer.
ElementName	Gets or sets the name of the generated XML element.
Form	Gets or sets a value that indicates whether the element is qualified.
IsNullable	Gets or sets a value that indicates whether the XmlSerializer must serialize a member that is set to null as an empty tag with the xsi:nil attribute set to true.
Namespace	Gets or sets the namespace assigned to the XML element that results when the class is serialized.
Order	Gets or sets the explicit order in which the elements are serialized or deserialized.
Type	Gets or sets the object type used to represent the XML element.
TypeId	When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute)

Methods

Equals(Object)	Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute)
GetHashCode()	Returns the hash code for this instance. (Inherited from Attribute)
GetType()	Gets the Type of the current instance. (Inherited from Object)
IsDefaultAttribute()	When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute)
Match(Object)	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

Applies to

See also

• XmlArrayAttribute
• XmlAttributeOverrides
• XmlAttributes
• XmlElementAttributes
• XmlElements
• XmlRootAttribute
• XmlSerializer
• Introducing XML Serialization
• How to: Specify an Alternate Element Name for an XML Stream
• Controlling XML Serialization Using Attributes
• Examples of XML Serialization
• XML Schema Definition Tool (Xsd.exe)