Articolo
11/18/2011

XmlWriter.LookupPrefix Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

When overridden in a derived class, returns the closest prefix defined in the current namespace scope for the namespace URI.

Namespace: System.Xml
Assembly: System.Xml (in System.Xml.dll)

Syntax

'Declaration
Public MustOverride Function LookupPrefix ( _
    ns As String _
) As String

public abstract string LookupPrefix(
    string ns
)

Parameters

ns
Type: System.String
The namespace URI whose prefix you want to find.

Return Value

Type: System.String
The matching prefix or nulla null reference (Nothing in Visual Basic) if no matching namespace URI is found in the current scope.

Exceptions

Exception	Condition
ArgumentException	ns is either nulla null reference (Nothing in Visual Basic) or String.Empty.

Examples

Dim output As New StringBuilder()

Dim settings As New XmlWriterSettings()
settings.Indent = True
Using writer = XmlWriter.Create(output, settings)
    writer.WriteComment("sample XML fragment")

    ' Write an element (this one is the root).
    writer.WriteStartElement("book")

    ' Write the namespace declaration.
    writer.WriteAttributeString("xmlns", "bk", Nothing, "urn:samples")

    ' Write the genre attribute.
    writer.WriteAttributeString("genre", "novel")

    ' Write the title.
    writer.WriteStartElement("title")
    writer.WriteString("The Handmaid's Tale")
    writer.WriteEndElement()

    ' Write the price.
    writer.WriteElementString("price", "19.95")

    ' Lookup the prefix and write the ISBN element.
    Dim prefix As String = writer.LookupPrefix("urn:samples")
    writer.WriteStartElement(prefix, "ISBN", "urn:samples")
    writer.WriteString("1-861003-78")
    writer.WriteEndElement()

    ' Write the style element (shows a different way to handle prefixes).
    writer.WriteElementString("style", "urn:samples", "hardcover")

    ' Write the close tag for the root element.
    writer.WriteEndElement()

    ' Write the XML to file.
    writer.Flush()
End Using

OutputTextBlock.Text = output.ToString()


StringBuilder output = new StringBuilder();

XmlWriterSettings settings = new XmlWriterSettings();
settings.Indent = true;
using (XmlWriter writer = XmlWriter.Create(output, settings))
{
    writer.WriteComment("sample XML fragment");

    // Write an element (this one is the root).
    writer.WriteStartElement("book");

    // Write the namespace declaration.
    writer.WriteAttributeString("xmlns", "bk", null, "urn:samples");

    // Write the genre attribute.
    writer.WriteAttributeString("genre", "novel");

    // Write the title.
    writer.WriteStartElement("title");
    writer.WriteString("The Handmaid's Tale");
    writer.WriteEndElement();

    // Write the price.
    writer.WriteElementString("price", "19.95");

    // Lookup the prefix and write the ISBN element.
    string prefix = writer.LookupPrefix("urn:samples");
    writer.WriteStartElement(prefix, "ISBN", "urn:samples");
    writer.WriteString("1-861003-78");
    writer.WriteEndElement();

    // Write the style element (shows a different way to handle prefixes).
    writer.WriteElementString("style", "urn:samples", "hardcover");

    // Write the close tag for the root element.
    writer.WriteEndElement();

    // Write the XML to file.
    writer.Flush();
}

OutputTextBlock.Text = output.ToString();

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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