XmlReader.Read Method

Definition

Namespace:

System.Xml

Assembly:

System.Xml.ReaderWriter.dll

Source:

XmlReader.cs

When overridden in a derived class, reads the next node from the stream.

public:
 abstract bool Read();

public abstract bool Read ();

abstract member Read : unit -> bool

Public MustOverride Function Read () As Boolean

Returns

Boolean

true if the next node was read successfully; otherwise, false.

Exceptions

XmlException

An error occurred while parsing the XML.

InvalidOperationException

An XmlReader method was called before a previous asynchronous operation finished. In this case, InvalidOperationException is thrown with the message "An asynchronous operation is already in progress."

Examples

The following example reads an XML file and displays each of the nodes:

XmlReaderSettings settings = new XmlReaderSettings();
settings.DtdProcessing = DtdProcessing.Parse;
XmlReader reader = XmlReader.Create("items.xml", settings);

reader.MoveToContent();
  // Parse the file and display each of the nodes.
  while (reader.Read()) {
    switch (reader.NodeType) {
      case XmlNodeType.Element:
          Console.Write("<{0}>", reader.Name);
          break;
      case XmlNodeType.Text:
          Console.Write(reader.Value);
          break;
       case XmlNodeType.CDATA:
           Console.Write("<![CDATA[{0}]]>", reader.Value);
           break;
       case XmlNodeType.ProcessingInstruction:
           Console.Write("<?{0} {1}?>", reader.Name, reader.Value);
           break;
       case XmlNodeType.Comment:
           Console.Write("<!--{0}-->", reader.Value);
           break;
       case XmlNodeType.XmlDeclaration:
           Console.Write("<?xml version='1.0'?>");
           break;
       case XmlNodeType.Document:
           break;
       case XmlNodeType.DocumentType:
           Console.Write("<!DOCTYPE {0} [{1}]", reader.Name, reader.Value);
           break;
       case XmlNodeType.EntityReference:
           Console.Write(reader.Name);
           break;
       case XmlNodeType.EndElement:
           Console.Write("</{0}>", reader.Name);
           break;
   }
}

Dim settings As New XmlReaderSettings()
settings.DtdProcessing = DtdProcessing.Parse
Dim reader As XmlReader = XmlReader.Create("items.xml", settings)
reader.MoveToContent()
' Parse the file and display each of the nodes.
While reader.Read()
  Select Case reader.NodeType
    Case XmlNodeType.Element
      Console.Write("<{0}>", reader.Name)
    Case XmlNodeType.Text
      Console.Write(reader.Value)
    Case XmlNodeType.CDATA
      Console.Write("<![CDATA[{0}]]>", reader.Value)
    Case XmlNodeType.ProcessingInstruction
      Console.Write("<?{0} {1}?>", reader.Name, reader.Value)
    Case XmlNodeType.Comment
      Console.Write("<!--{0}-->", reader.Value)
    Case XmlNodeType.XmlDeclaration
      Console.Write("<?xml version='1.0'?>")
    Case XmlNodeType.Document
    Case XmlNodeType.DocumentType
      Console.Write("<!DOCTYPE {0} [{1}]", reader.Name, reader.Value)
    Case XmlNodeType.EntityReference
      Console.Write(reader.Name)
    Case XmlNodeType.EndElement
      Console.Write("</{0}>", reader.Name)
  End Select
End While

The sample uses the items.xml file.

<?xml version="1.0"?>
<!-- This is a sample XML document -->
<!DOCTYPE Items [<!ENTITY number "123">]>
<Items>
  <Item>Test with an entity: &number;</Item>
  <Item>Test with a child element <more/> stuff</Item>
  <Item>Test with a CDATA section <![CDATA[<456>]]> def</Item>
  <Item>Test with a char entity: A</Item>
  <!-- Fourteen chars in this element.-->
  <Item>1234567890ABCD</Item>
</Items>

Output:

<Item>Test with an entity: 123</Item><Item>Test with a child element <more> stuff</Item><Item>Test with a CDATA section <![CDATA[<456>]]> def</Item><Item>Test with a char entity: A</Item><!-- Fourteen chars in this element.--><Item>1234567890ABCD</Item></Items>

Remarks

When an XmlReader is first created and initialized, there is no information available. You must call Read to read the first node. The Read method sets the state of the XML reader to initiate ReadState.Initial and moves through the XML file sequentially until it reaches the end of the file, at which point the method returns a value of false.

This method requires at least four bytes from the data stream in order to begin parsing. If fewer than four bytes are returned and there is no more data in the stream, the method returns false. If there is more data in the stream, the method will block parsing until receipt of the fourth byte.

For the asynchronous version of this method, see ReadAsync.