NETWORK COMMUNICATION in VB.NET

Creating Quick Response Code in VB.NET NETWORK COMMUNICATION

Note From a security prospective, the includeExceptionDetailInFaults="true" WCF configuration should

never be deployed in production environments. It exposes sensitive server-side data such as the exception type and stack trace, which present a security risk.

Finally, in the GetBookInfo.svc.cs service code-behind file, we add the following lines of code to throw a fault of type BookNotFound in the case where the entered title does not match any of the titles in our books array object. BookNotFound fault = new BookNotFound(); fault.NotFoundMessage= "Book not found"; throw new FaultException<BookNotFound> (fault, new FaultReason ("Reason: Book not found fault occurred.")); Note that here we supplied the custom FaultReason message, otherwise FaultException will say that The creator of this fault did not specify a reason. It is good practice to supply a proper reason to identify the type of fault that has occurred, when you can have multiple fault types. As we modified the GetBookInfo service, similarly we need to update the proxy class. At this point, you need to regenerate a GetBookInfo.cs proxy class file using slsvcutil.exe (or within Visual Studio 2010, adding it by Add/Update Service Reference), as described previously, and replace the existing file with this new one in the chapter5 Silverlight project. While generating a proxy class to the GetBookInfo service, it will generate code for the BookNotFound class since it was exposed in the service metadata. This enables the class to be used inside the Silverlight client and drive the programming logic. Now we need to add reference by adding using chapter5.Web in the namespace section of MainPage.xaml.cs and modifying the GetBook_GetByTitleCompleted event handler as shown here. void GetBook_GetByTitleCompleted (object sender, GetByTitleCompletedEventArgs e) { if (e.Error==null) { InfoPanel.DataContext = e.Result; } else if (e.Error is FaultException<GetBookInfoBookNotFound >) { FaultException<GetBookInfoBookNotFound> fault = e.Error as FaultException<GetBookInfoBookNotFound>; MessageBox.Show (fault.Detail.NotFoundMessage,"Error has occurred",0); } } Here we place an if condition to check whether GetByTitleCompletedEventArgs e contains any Error. If it contains an error and if it is FaultException of type GetBookInfoBookNotFound, then we cast the e.Error to GetBookInfoBookNotFound object fault and show the MessageBox box with the message set to NotFoundMessage fault object.

Rebuild the solution and press F5 (or Ctrl + F5 if you don t want Visual Studio to break on FaultException) and enter some string that does not match the title of any book we previously stored in the books array and press the Get Book detail button. Notice that this time a custom fault occurred at the GetBookInfo WCF service level, and a custom Book not found message is displayed rather than the default Not found message.

Note Get more details on creating and handling faults in Silverlight by visiting the Microsoft MSDN web site at

Two classes are provided to support direct communication over HTTP: System.Net.WebClient and System.Net.HttpWebRequest. WebClient is simpler but exposes only simplified access to the GET and POST methods of HTTP. WebClient is most useful for easily downloading resources. The HttpWebRequest class provides greater control over HTTP communication.

The WebClient class provides simplified access to communicating over HTTP (it is located in the System.Net assembly). Its most important members are listed in Table 5-3. Table 5-3. Members of the System.Net.WebClient Class

DownloadStringAsync DownloadStringCompleted UploadStringAsync UploadStringCompleted OpenReadAsync OpenReadCompleted DownloadProgressChanged

Asynchronously downloads data and returns it as a string. Occurs when DownloadStringAsync is complete. Asynchronously uploads a string to a specified URI. Occurs when UploadStringAsync is complete. Asynchronously downloads data and returns it as a Stream. Occurs when OpenReadAsync is complete. Occurs when some/all data is transferred. This is useful for building a status indicator such as a download progress bar. Occurs when some/all data is uploaded. This is useful for building a status indicator such as an upload progress bar. Used to cancel an already-issued asynchronous operation.