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

The XmlTextWriter object is still a stream-based component that needs a destination towrite to. Unlike the Bitmap object, however, the XmlTextWriter object can be forced towrite the output to a string. To do that, you initialize the XML text writer with an instanceof the StringWriter object. The final string with the XML code can be obtained with a callto the StringWriter object's ToString method.The format of the XML text returned is shown here:FFD8FF...E00010Notice that the comment and the size of the file are strictly call-specific parameters. TheSize attribute refers to the size of the BinHex-encoded text. As you'd expect, this valueis significantly larger than JPEG size. Having that value available is not strictlynecessary, but once it's on the client, it can simplify the task of transforming the XMLstream back into a JPEG image.StringWriter and Unicode EncodingThe XML output generated by the GetSalesReportBarChart method uses the Unicodeencoding scheme—UTF-16—instead of the default UTF-8. This would be fine if not forthe fact that Microsoft Internet Explorer returns an error when you double-click theXML file. The error has nothing to do with the XML itself; it is more a bug (or perhapseven a feature) of Internet Explorer and the internal style sheet Internet Explorer usesto display XML documents.In general, UTF-16 is used whenever you write XML text to a StringWriter object.When a TextWriter object (StringWriter inherits from TextWriter) is passed to theXmlTextWriter constructor, no explicit encoding argument is allowed. In this case, theXmlTextWriter object transparently inherits the encoding set contained in the writerobject being passed. The StringWriter class hard-codes its Encoding property to UTF-16—there's no way for you to change it, because the property is marked as read-only.If you want to generate XML strings with an encoding scheme other than UTF-16,drop StringWriter objects in favor of memory streams.The helper class shared by the remotable object and the Web service is now ready touse. Let's look more closely at the remote service component.Writing the Remote Service ComponentAs mentioned, a remotable component has just one requirement: the class thatrepresents the object must be inherited from MarshalByRefObject. Unless you need toexercise stricter control over the object lifetime, you don't need to override any of themethods defined in the base class for MBR objects.Apart from the parent class, a remotable class is not different from any other class inthe .NET Framework. All of its public methods are callable by clients, the class canimplement any number and any type of interfaces, and the class can reference anyother external class.Because we already put all the core code in the SalesDataProvider class, writing theremote service class—ServiceSalesProvider—is a snap. The class is a simple wrapperfor SalesDataProvider, as shown here:public class ServiceSalesProvider : MarshalByRefObject437