Creating XML Readers
XmlReader instances are created using the Create method. The XmlReaderSettings class is used to specify the set of features you want to enable on the XmlReader object.
.gif "Important note") Important Note: |
|---|
Although the Microsoft .NET Framework includes concrete implementations of the XmlReader class, such as the XmlTextReader, XmlNodeReader, and the XmlValidatingReader classes, in the .NET Framework version 2.0, we recommend that you create XmlReader instances using the Create method. |
Features are enabled or disabled by using the properties on the XmlReaderSettings class. The XmlReaderSettings object is then passed to the Create method.
By using the Create method and the XmlReaderSettings class you get the following benefits:
You are able to specify which features you want supported on the created XmlReader object.
The XmlReaderSettings class can be reused to create multiple reader objects. You can use the same settings to create multiple readers with the same functionality. Alternatively, you can modify the XmlReaderSettings object and create a new reader with a different set of features.
You can add features to an existing reader. The Create method can accept another XmlReader object. The underlying XmlReader object can be a user-defined reader or an XmlTextReader object, or another XmlReader instance that you want to add additional features to.
Take full advantage of all the new features added to the XmlReader class in the .NET Framework 2.0 release. There are certain features, such as better conformance checking and compliance to the XML 1.0 recommendation, that are available only on XmlReader objects created by the Create method.
The following table lists the default property settings on the XmlReaderSettings class.
Property |
Default value |
|---|---|
true |
|
ConformanceLevel.Document |
|
false |
|
false |
|
false |
|
0. |
|
0 |
|
null |
|
true |
|
An empty XmlSchemaSet object |
|
ProcessIdentityConstraints enabled |
|
ValidationType.None |
|
A new XmlUrlResolver object |
XmlReader Scenarios
The following table describes some common scenarios and which settings on the XmlReaderSettings class to apply.
Scenario |
XmlReaderSettings |
|---|---|
Requires the data to be a well-formed XML document. |
ConformanceLevel = ConformanceLevel.Document |
Requires the data to be a well-formed XML parsed entity. |
ConformanceLevel = ConformanceLevel.Fragment |
Needs data to be validated against a DTD. |
ProhibitDtd = false ValidationType = ValidationType.DTD |
Needs data to be validated against an XML Schema. |
ValidationType = ValidationType.Schema Schemas = XmlSchemaSet to use for validation |
Needs data to be validated against an inline XML Schema. |
ValidationType = ValidationType.Schema ValidationFlags |= XmlSchemaValidationFlags.ProcessInlineSchema |
Needs type support. |
ValidationType = ValidationType.Schema Schemas = XmlSchemaSet to use |
There are a few special scenarios that may require using an XmlReader implementation that is not created by the Create method.
- If you must validate against an XDR schema, use the XmlValidatingReader class.
Note
The XmlValidatingReader class is obsolete in the .NET Framework 2.0 release. We recommend that you consider migrating to XML Schemas and validate using an XmlReader object returned by the Create method.
To read XML data from an XmlNode object, use the XmlNodeReader class.
If you must expand entities on request (readers created by the Create method expand all entities), or if you do not want your text content normalized, use the XmlTextReader class.
If you do not want default attributes returned, use the XmlTextReader class.
To instantiate an XmlReader object
Dim settings As New XmlReaderSettings()
settings.ConformanceLevel = ConformanceLevel.Fragment
settings.IgnoreWhitespace = true
settings.IgnoreComments = true
Dim reader As XmlReader = XmlReader.Create("books.xml", settings)
XmlReaderSettings settings = new XmlReaderSettings();
settings.ConformanceLevel = ConformanceLevel.Fragment;
settings.IgnoreWhitespace = true;
settings.IgnoreComments = true;
XmlReader reader = XmlReader.Create("books.xml", settings);
To wrap a reader instance within another reader
Dim txtReader As XmlTextReader = New XmlTextReader("bookOrder.xml")
Dim settings As New XmlReaderSettings()
settings.Schemas.Add("urn:po-schema", "PO.xsd")
settings.ValidationType = ValidationType.Schema
Dim reader As XmlReader = XmlReader.Create(txtReader, settings)
XmlTextReader txtReader = new XmlTextReader("bookOrder.xml");
XmlReaderSettings settings = new XmlReaderSettings();
settings.Schemas.Add("urn:po-schema", "PO.xsd");
settings.ValidationType = ValidationType.Schema;
XmlReader reader = XmlReader.Create(txtReader, settings);
To chain readers to add additional settings
Dim settings As New XmlReaderSettings()
settings.ValidationType = ValidationType.DTD
Dim inner As XmlReader = XmlReader.Create("book.xml", settings) ' DTD Validation
settings.Schemas.Add("urn:book-schema", "book.xsd")
settings.ValidationType = ValidationType.Schema
Dim outer As XmlReader = XmlReader.Create(inner, settings) ' XML Schema Validation
XmlReaderSettings settings = new XmlReaderSettings();
settings.ValidationType = ValidationType.DTD;
XmlReader inner = XmlReader.Create("book.xml", settings); // DTD Validation
settings.Schemas.Add("urn:book-schema", "book.xsd");
settings.ValidationType = ValidationType.Schema;
XmlReader outer = XmlReader.Create(inner, settings); // XML Schema Validation