Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

The preceding code creates an attribute override based on an element namedFamilyName. This new element is added to an attribute overrides collection. Inparticular, the FamilyName attribute overrides the LastName element on the Employeetype. The following code snippet shows how to hide a source element—in this case,FirstName:SoapAttributes attrib2 = new SoapAttributes();attrib2.SoapIgnore = true;sao.Add(typeof(Employee), "FirstName", attrib2);The attribute overrides are gathered in the SoapAttributeOverrides collection, which isthen used to initialize the SoapReflectionImporter class, as shown here, and then canbe used in the type mapping in the serializer:SoapReflectionImporter imp = new SoapReflectionImporter(sao);We'll return to this topic in the section "XML Serialization Attributes," on page 499. Inparticular, you'll learn how to add type information to plain XML serialization, when noSOAP-encoded types are involved.Deserializing XML Data to ObjectsThe deserialization process is controlled by the Deserialize method for a variety ofsources, including streams, XML readers, and text readers. Remember that by usingthe trick discussed in Chapter 2 for XML readers (packing a string into a StringReaderobject), you can also easily deserialize from strings.Although officially you can deserialize from streams and text readers, thedeserialization process is actually a matter of invoking an XML reader—more precisely,a very special breed of XML reader, optimized for serialization and for the specific classinvolved. Connected to the deserialization process is the Can-Deserialize method. Thismethod returns a Boolean value indicating whether the XML reader is correctlypositioned on the start element of the XML data. In addition, CanDeserialize ensuresthat the start element of the XML data is compatible with the originally saved class.Normally, you call CanDeserialize in the context of a more general strategy designed totrap as many errors and exceptions as possible. If the application always deserializesdata that the XML serializer has previously created, a call to CanDeserialize can easilybe redundant. The call becomes crucial, how-ever, as soon as your application beginsto deserialize XML data whose genuineness and quality are not guaranteed. It is worthnoting that CanDeserialize works only on XML readers, whereas Deserialize cansuccessfully handle streams and text readers too.From a programming perspective, deserializing is not rocket science, as the followingcode clearly demonstrates:StreamReader reader = new StreamReader(fileName);Employee emp = (Employee) ser.Deserialize(reader);reader.Close();During the deserialization stage, a few events can be fired. In particular, theUnknownElement, UnknownAttribute, and UnknownNode events signal when unknownand unexpected nodes are found in the XML text being deserialized. TheUnknownNode event is more generic than the other two and triggers regardless of thenode type on which the exception is detected. In case of unknown element or attributenodes, the UnknownNode event is fired first.404