ASP.NET Web PDF Document Viewer/Editor Control Library

Figure 2-17. Display Value My Block Figure 2-18 shows the Display Value block in a test program. The configuration window for the block shows how the Label can be entered, and checking the box in the Clear field will cause the NXT to clear the entire screen before writing the new value.

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Figure 10-4. Invoking a dynamic WCF service Another interesting reason to host services in a program is to create desktop applications that can listen for updates for some kind of central server. Traditionally, these kinds of applications have been to poll central server, which can lead to a large amount of unnecessary network traffic if polling is too frequent. Listing 10-14 demonstrates how to do this. It shows a blank form that hosts a service that will listen to updates from a client; in this case, the update will be a background image to display. The service defines one function, ReceiveImage, which receives that binary data that makes up an image. The implementation of the service raises an event, newImgEvent, every time an image is received; this is so that the form can be updated every time a new image is received. Hooking the form up to the event is straightforward: newImgEvent.Add(fun img -> form.BackgroundImage <- img) You just need to call the event s Add method and pass it a function that updates the form. You will notice that the code required to host the service (that is, the code that defines myServiceHost) is unchanged from the previous example.

The Internet has certainly evolved from its early origins as a way for researchers to connect and share information. The Internet began with simple textual browsers and static pages, but it is now hard to find a company that doesn t have a polished Web site. In its early days, who could have possibly imagined that people would one day flock to the Internet to research that new car or buy the latest Stephen King novel Developers fed up with the difficulty of deploying thick client applications to thousands of users looked to the Web to ease their burden. Several Web application technologies have been developed over the years some proprietary, others requiring significant programming abilities. Though some provided a richer user experience than others, no one would confuse a thin client application with its desktop-based cousin. Still, the ease of deployment, the ability 3565005953993bd3170c41194f12907b to reach a wider customer base, and the lower cost of maintenance means that despite the limitations of browsers, they are still the target platform of choice for many applications.

Listing 10-14. A Windows Form with a Service Built In #light open System open System.IO open System.Drawing open System.ServiceModel open System.Windows.Forms [<ServiceContract (Namespace = "http://strangelights.com/FSharp/Foundations/WCFImageService")>] type IImageService = interface [<OperationContract>] abstract ReceiveImage : image:array<Byte> -> unit end let newImgTrigger, newImgEvent = IEvent.create<Bitmap>() type ImageService() = class interface IImageService with member x.ReceiveImage( image ) = let memStream = new MemoryStream(image) let bitmap = new Bitmap(memStream) newImgTrigger bitmap end end let myServiceHost = let baseAddress = new Uri("http://localhost:8080/service") let temp = new ServiceHost((type ImageService), [|baseAddress|]) let binding = let temp = new WSHttpBinding(Name = "binding1", HostNameComparisonMode = HostNameComparisonMode.StrongWildcard, TransactionFlow = false) temp.Security.Mode <- SecurityMode.Message temp.ReliableSession.Enabled <- false temp temp.AddServiceEndpoint((type IImageService), binding, baseAddress) |> ignore temp myServiceHost.Open()

The screen output of this program is shown in Figure 2-19.

You have already seen that the server doesn t necessarily need to send the response in XML format. It s perfectly legal to send the response as simple text as long as the Content-Type response header is set to text/plain, as opposed to text/xml for XML. Complex data structures are good candidates to be sent in XML format. Modern browsers have consistently good support for navigating an XML document and also for modifying the XML document s structure and contents. How exactly does the browser handle XML returned by the server Modern browsers treat the XML as an XML document in accordance with the W3C DOM. The W3C DOM specifies a rich set of APIs for searching and manipulating XML documents. DOM-compliant browsers