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194 CHAPTER 6 DECOUPLED NAVIGATION PATTERN E B V N Figure 6-20. Pop-up box HTML component details Pattern Highlights Based on its description in the Architecture section, the Decoupled Navigation pattern might seem unnecessary. However, the usefulness of this pattern became obvious in the Implementation section. With Ajax, complex web applications are going to be written that navigate very sophisticated data. Navigating the content means using some type of link, and logic on the client side, and that is the heart of the Decoupled Navigation pattern in that it aims to organize and decouple the various pieces of the logic. All of this was illustrated by an example that became progressively more complex. The essence of this pattern is to focus on the client side and to break apart the pieces of an HTML application so that maintenance, extensibility, and coding are simpler and can be overseen. The fact is that many HTML applications are complicated, and maintaining oversight of these applications is imperative. For each of the functionalities, there are some rules of thumb. For the Action functionality, the following rules are defined: Use the id property to uniquely identify all HTML elements that will be used in the application. The HTML event object instance should be abstracted for simplicity and robustness.
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CHAPTER 6 DECOUPLED NAVIGATION PATTERN E B V N Figure 6-19. Example HTML components for dynamic content Let s illustrate how to integrate the pop-up box HTML content and inspect the related HTML page (see Figure 6-20). Figure 6-20 shows two text boxes that have been highlighted. The upper text box contains the common code that can be stored in a separate JavaScript file. The lower text box contains the user example code that is created as a prototype of how to invoke the common code. When implementing the Presentation functionality, the common code is not touched and is treated as its own module. What is touched and modified is the user example code. The clear separation of the common code and the code used to invoke the common code is a very good HTML component. Such a definition of an HTML component indicates that the HTML component has been decoupled and can be plugged into an unrelated infrastructure. One of my pet peeves with many web application and Ajax frameworks is that they are not decoupled. Often the client-side technology relies on server-side technologies, and the client is coupled with other pieces on the HTML page. The result is a monolithic application that happens to function as a web application and Ajax application. However, these applications miss the main thrust of the Ajax and REST philosophies.
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192 CHAPTER 6 DECOUPLED NAVIGATION PATTERN For the event call nav.call, the new function is PopupDialogbox and it is defined as follows: function PopupDialogbox( common, state) { InjectHTML( common, state); document.getElementById( “showimage”).style.visibility = “visible”; document.getElementById( “title”).innerHTML = state.title; } The function PopupDialogbox is an adapter of the predefined pop-up box component. By using the function InjectHTML, you inject the text in the table cell destination, destContent. The first getElementById references the property visibility and is used to make the div HTML element appear. The second getElementById references the innerHTML property and is used to assign the title of the pop-up box. The title would be assigned in the common.complete function implementation. In the example, PopupDialogbox is a function defined in the HTML page itself. But there is no reason why the function could not be reused in different contexts whenever a pop-up box is necessary. Additionally, the PopupDialogbox function needs other cosmetic changes, such as orientation and size of the pop-up box, that are not illustrated. The changes are not illustrated because they are application specific and do not help explain the Decoupled Navigation pattern. Using HTML Components When I was writing the details of this pattern, I was reluctant to repeat content that was written E B V N in great detail in other books or websites. After all, providing a bunch of widgets and their explanations without going into great detail is a very bad idea. However, I also knew that the Presentation functionality requires the explanation of HTML components. My original idea was to spend pages and pages explaining some basic HTML components such as pop-up boxes, menus, and pop-up windows. So off I went to explore how other people were building these HTML components. During my exploration, I hit upon the website http:// www.dynamicdrive.com. At first I thought, interesting site and neat components. It did not have everything, but it was good. It was not until I had to start explaining how to create HTML components that I realized the brilliance of this website. I thought I would have to spend hours integrating a pop-up box into the Decoupled Navigation pattern, when in fact it required only 20 minutes. At that point, it hit me that the best way to explain the Presentation functionality was to explain how to integrate HTML components. But as my exploration continued, I learned that there were good HTML components and bad HTML components. So as part of the implementation of the Decoupled Navigation pattern, I want to explain a good HTML component site so that when you are exploring for your own HTML components, you will be able to gauge a good or bad HTML component. After all, you do not want to write your own pop-up box. It has been done often enough. Figure 6-19 is a snapshot of the http://www.dynamicdrive.com website, which lists the available HTML components for dynamic content.
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CHAPTER 6 DECOUPLED NAVIGATION PATTERN
Announcement Box

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