.NET/Java PDF, Tiff, Barcode SDK Library

Each method in the interface that defines an operation offered by the service must be marked with an OperationContract. You might have thought that it would be enough that the interface is marked as ServiceContract why do we also need to annotate each method WCF requires you to be explicit so that it s always obvious when you re defining some aspect of your system that will be visible across the network. A method call to a local object is a quite different kind of operation than using a remote service the performance and reliability characteristics are poles apart so it s important for such boundaries to be clearly visible in the code.

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Let s take a look at the markup that is used to implement this: <li id="PHItem"> <div id="PHDiv"> <table cellspacing='0' cellpadding='0' class='style1' style='border-width: 0'> <tr class='style2'> <td style='background-color: #1077ad; ' width="100px"> Date</td> <td style='background-color: #1077ad; ' width="100px"> Price</td> </tr> </table> </div> <div id="PHContents"> <atlas:UpdatePanel ID="THTextPanel" runat="server"> <ContentTemplate> <asp:Panel ID="Panel1" runat="Server" ScrollBars="auto" Width="200px" Height="100px"> <asp:Label ID="lblPH" runat="server" Text=""></asp:Label> </asp:Panel> </ContentTemplate> </atlas:UpdatePanel>

Although we re defining a method for each operation, ultimately the contract defines what messages can go in and out of the service. To invoke an operation, a client will need to send a message to the server over the network. When you add a method marked with OperationCon tract to an interface marked with ServiceContract, you are really defining the logical structure of the message that will be sent to invoke that operation, and also of the message that will be sent back to the client when the operation is complete. WCF lets you represent these message formats as method signatures because it s a convenient abstraction for developers. WCF supports other ways of defining message formats you can write a contract in WSDL, the Web Service Definition Language, and then generate types from that. This approach is beyond the scope of this book.

The CONFIG variable is used to control what type of library is being built. A dynamic library is built by adding the value dll. Other possible values are staticlib, which builds a static library, and plugin, which is used to build plugins. Notice that adding the value plugin implicitly adds the dll value as well because a plugin is a dynamic library. Listing 15-3. A project file for building a library TEMPLATE = lib TARGET = mylib VERSION = 1.0.0 CONFIG += dll HEADERS += mylib.h SOURCES += mylib.cpp The file name extensions used for libraries differ between different platforms and compilers (it is all handled by QMake). For example, never specify the file name extension to the TARGET variable; let QMake handle it instead.

Our service is designed to let people chat, so it will need to provide clients with a way to send a short bit of text, which we ll refer to as a note. (A more obvious name would be message, but that would introduce ambiguity WCF sends messages to and from the server for every operation, so to call one of the pieces of information that crops up

in certain messages a message would be confusing.) To keep things simple, we ll just have one big chat room where everyone can see every note; we re not going to support private conversations. To support sending notes, we ll get rid of the DoWork method provided by Visual Studio, and replace it with the code in Example 13-2.

[OperationContract] void PostNote(string from, string note);

It is usually enough to build a library or an application, but sometimes your project consists of several parts resulting in several libraries and several applications. QMake is powerful enough to handle these situations as well. Let s have a look at how it can look. The project shown here consists of a library and an application. The library is called base, and the application is called app. The files of the project are structured as shown in Listing 15-4. The master project file, complex.pro, is located at the base level, along with the directories bin, lib, app, include, and src. The bin and lib directories are empty. The app directory contains the source code and project file for the application. The include directory contains the header files for the library; that is, the headers shared between the library and the application. The src directory contains the source code and project file for the library. The two empty directories, lib and bin, are intended for the library built from the contents of src and the resulting application binary from app, respectively.

If you attempt to build your project in Visual Studio, you ll get a compiler error:

error CS0535: 'ChatServerLibrary.ChatService' does not implement interface member 'ChatServerLibrary.IChatService.PostNote(string, string)'

Remember that Visual Studio added two files: IChatService.cs (the contract) and ChatService.cs (the service implementation). The compiler is pointing out to us that our service implementation no longer conforms to the contract for the service. So in ChatService.cs, we need to replace the DoWork method with this code: