Dragging and dropping in .NET framework

Generating PDF-417 2d barcode in .NET framework Dragging and dropping

application design strategies and the drag-and-drop implementation. For these reasons, the listings contain only the relevant portions of the code. Let s start with an overview of the logical layers that make up the ASP.NET web application. Then, we ll focus on some modifications you need to make to the BookItem and the CartZone controls in order to take advantage of the server-centric model. Finally, we ll concentrate on the Ajax-enabled controls that you ll use to represent the catalog and the shopping cart.

The shopping-cart application is designed as a three-tier application. This means server objects are organized into three logical layers that communicate with one another, as shown in figure 12.8. The presentation layer, at the top, contains the controls responsible for rendering the UI and handling the user s input and interactions. The business layer consists of the server classes that represent the entities involved in the application. In the shopping-cart application, for example, you have a Book class that represents a book article. The business objects manipulate and process the data obtained through the data access layer. Finally, the data access layer is used to access the data store and to query, retrieve, and update the data. In the example, the data store is an XML file, and the data access layer is responsible for building business objects from the raw XML data. These layers have a uniform view of the data.

Figure 12.8 Structure of a typical layered application. Layers form a chain and can communicate with one another.

Designing an application using layers allows for modularity and code reuse. You can find more information about this design pattern by browsing the following URL: http://msdn2.microsoft.com/en-us/library/ ms978496.aspx.

Let s see in more detail how we decided to implement the three layers that make up the shopping-cart web application. We made some design decisions with simplicity in mind, because our main goal is to focus on concepts. In real life, production-quality code might require different and more complex strategies. Data access layer To keep things simple, we decided to use an XML file as the data store. The XML file contains the catalog s data as a set of book nodes contained into a root book element. Listing 12.7 shows an excerpt from the BookCatalog.xml file, contained in the App_Data folder of the sample website.

< xml version="1.0" encoding="utf-8" > <books> <book> <id>0001</id> <title>AJAX In Action</title> <imageUrl>~/Images/crane_3d.gif</imageUrl> </book> <book> <id>0002</id> <title>iBATIS In Action</title> <imageUrl>~/Images/begin_3d.gif</imageUrl> </book> </books>

Each book node contains an id element with the book ID, a title element that contains the book s title, and an imageUrl element with the path to the image used in the catalog. Pretty simple, but it s enough for our purposes. Business layer The business objects used in the example are a Book class and a ShoppingCart class. The Book class impleIShoppingCart IArticle ments an interface called IArticle, which defines a set of properties common to generic articles or the catalog. Book ShoppingCart The ShoppingCart class implements the IShoppingCart interface, which defines a single method called Add, used to add an article to the cart. Fig- Figure 12.9 Hierarchy of business objects used in the drag-and-drop shopping cart example ure 12.9 shows the hierarchy of business objects used in the example. To keep things simple, the business objects provider is implemented with a class called BusinessLayer that exposes some static methods for accessing the XML file. The GetBooks methods returns all the books in the catalog, and the GetBooksById method returns the Book object corresponding to the given book s ID. Presentation layer The presentation layer consists of two web user controls called ShoppingCart.ascx and BooksCatalog.ascx. The first control encapsulates the HTML and