[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.ReturnValue)] |
The XmlNamespaceDeclarationsAttribute allows you to store the prefixes, and the associated namespaces, used in an XML document. For example, one common usage of the attribute is to store XPath data, as it is defined by the World Wide Web Consortium (www.w3.org) document named "XML Language (XPath) Version 1.0". In brief, an XPath is a string containing many namespace prefixes and local names, along with some other syntax.
The XPath language allows for the association of a prefix with a path, and using the prefix within the XML document. For example, the following XML document named "select" contains a prefix ("cal") associated with a specific URI (http://www.cohowinery.com/calendar/). The element contains an attribute named "path" that contains the XPath.
<select xmlns:cal ="http://www.cohowinery.com/calendar/" path="cal:appointments/@startTime" />
The schema for this might be:
<element name="select">
<complexType>
<simpleContent>
<attribute name="path" />
</simpleContent>
</complexType>
</element>
Without the XmlNamespaceDeclarationsAttribute, the association between the prefix and the namespace would be lost.
To retain the association between the prefix and the namespace URI, add a member that returns an XmlSerializerNamespaces object and apply the XmlNamespaceDeclarationsAttribute attribute to the member, as shown in the following C# and Visual Basic code:
// C#
public class Select {
[XmlAttribute] public string path;
[XmlNamespaceDeclarations] public XmlSerializerNamespaces xmlns;
}
' Visual Basic
Public Class Select
<XmlAttribute> Public path As String
<XmlNamespaceDeclarations> Public xmlns As XmlSerializerNamespaces
End Class
When serialized, the schema for the generated XML document will contain the XML Schema definition (XSD) element named
appinfo
. The element further contains a metadata element named
keepNamespaceDeclarations
, set to the name of the member that contains the namespace declarations. The schema for such an XML document is shown below:
<xs:element name="select">
<xs:complexType>
<xs:annotation>
<xs:appinfo>
<keepNamespaceDeclarations>xmlns</keepNamespaceDeclarations>
</xs:appinfo>
</xs:annotation>
<xs:simpleContent>
<xs:attribute name="path" />
</xs:simpleContent>
</xs:complexType>
</xs:element>
On deserialization, the
xmlns
field will contain an XmlSerializerNamespaces object containing all namespace prefix definitions.
On serialization, the user can add prefix-namespace pairs to the XmlSerializerNamespaces object using the XmlSerializerNamespaces.Add method. This is shown in the C# and Visual Basic code below:
// C#
using System;
using System.IO;
using System.Xml.Serialization;
[XmlRoot("select")]
public class Select {
[XmlAttribute]
public string xpath;
[XmlNamespaceDeclarations]
public XmlSerializerNamespaces xmlns;
}
public class Test {
public static void Main(string[] args) {
Select mySelect = new Select();
mySelect.xpath = "myNS:ref/@common:y";
mySelect.xmlns = new XmlSerializerNamespaces();
mySelect.xmlns.Add("MyNS", "myNS.tempuri.org");
mySelect.xmlns.Add("common", "common.tempuri.org");
XmlSerializer ser = new XmlSerializer(typeof(Select));
ser.Serialize(Console.Out, mySelect);
}
}
// Output:
// <?xml version="1.0" encoding="IBM437"?>
// <select xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
// xmlns:common="common.tempuri.org" xmlns:MyNS="myNS.tempuri.org" xpath="myNS:ref/@common:y" />
' Visual Basic
Imports System
Imports System.IO
Imports System.Xml.Serialization
<XmlRoot("select")> _
Public Class SelectPath
<XmlAttribute> _
Public xpath As String
<XmlNamespaceDeclarations> _
public xmlns As XmlSerializerNamespaces
End Class
Public Class Test
Public Shared Sub Main()
Dim mySelect As SelectPath = New SelectPath()
mySelect.xpath = "myNS:ref/@common:y"
mySelect.xmlns = New XmlSerializerNamespaces()
mySelect.xmlns.Add("MyNS", "myNS.tempuri.org")
mySelect.xmlns.Add("common", "common.tempuri.org")
Dim ser As XmlSerializer = New XmlSerializer(mySelect.GetType)
ser.Serialize(Console.Out, mySelect)
End Sub
End Class
'Output:
' <?xml version="1.0" encoding="IBM437"?>
' <select xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
' xmlns:common="common.tempuri.org" xmlns:MyNS="myNS.tempuri.org" xpath="myNS:ref/@common:y" />
Also note that the member to which the attribute is applied will contain only the prefix-namespace pairs belonging to the XML element defined by the class. For example, in the XML document shown below, only the prefix pair "cal" will be captured, but not the "x" prefix. To get that data, add a member with the XmlNamespaceDeclarationsAttribute to the class representing the
root
element.
<?xml version="1.0"?>
<x:root xmlns:x="http://www.cohowinery.com/x/">
<x:select xmlns:cal="http://www.cohowinery.com/calendar/" path="cal:appointments/@cal:startTime" />
</x:root>
| ctor #1 | Default constructor. This constructor is called by derived class constructors to initialize state in this type. Initializes a new instance of the XmlNamespaceDeclarationsAttribute class. |
| TypeId (inherited from System.Attribute) |
Read-only See base class member description: System.Attribute.TypeId When implemented in a derived class, gets a unique identifier for this Attribute. |
| Equals (inherited from System.Object) |
See base class member description: System.Object.Equals Derived from System.Object, the primary base class for all objects. |
| GetHashCode (inherited from System.Attribute) |
See base class member description: System.Attribute.GetHashCode Returns the hash code for this instance. |
| GetType (inherited from System.Object) |
See base class member description: System.Object.GetType Derived from System.Object, the primary base class for all objects. |
| IsDefaultAttribute (inherited from System.Attribute) |
See base class member description: System.Attribute.IsDefaultAttribute When overridden in a derived class, returns an indication whether the value of this instance is the default value for the derived class. |
| Match (inherited from System.Attribute) |
See base class member description: System.Attribute.Match When overridden in a derived class, returns a value indicating whether this instance equals a specified object. |
| ToString (inherited from System.Object) |
See base class member description: System.Object.ToString Derived from System.Object, the primary base class for all objects. |
| Finalize (inherited from System.Object) |
See base class member description: System.Object.Finalize Derived from System.Object, the primary base class for all objects. |
| MemberwiseClone (inherited from System.Object) |
See base class member description: System.Object.MemberwiseClone Derived from System.Object, the primary base class for all objects. |
Hierarchy:
public XmlNamespaceDeclarationsAttribute(); |
public virtual object TypeId {get;}
|
~XmlNamespaceDeclarationsAttribute(); |
public override int GetHashCode(); |
public Type GetType(); |
public virtual bool IsDefaultAttribute(); |
The implementation of this method in a derived class compares the value of this instance to a standard, default value obtained by some means, then returns a Boolean value that indicates whether the value of this instance is equal to the standard. The standard value is typically coded as a constant in the implementation, or stored programmatically in a field used by the implementation.
obj
protected object MemberwiseClone(); |
public virtual string ToString(); |