Dr. Dobb's Journal - February 2008 - (Page 63)

d02seku_p4ma 12/12/07 9:40 AM Page 63 Figure 3 shows the result of running this page. In this example, you can see some other techniques that are characteristic of the ZK environment. Similar to JSP, some default objects are available on ZUL pages. In the example, I used: • session, modeled on javax.servlet.http.HttpSession. • page, representing the object of the current page. • self, which points to the component where an event happened. Another defined variable inside the forEach loop is forEachStatus.index, which counts loop iterations. ZUL also offers the ability to define values of any component attribute in a special tag named . In the example, I used it to simplify a script that reacts to an onClick event. For every ZUL component, it is possible to define its own new attributes with the help of a tag. Such attributes can bear any Java objects as values. In the example, it allowed me to store the number of a row, and then identify it when the Delete key was clicked. An interesting functionality of the ZK framework is a class imitating the JOptionPane from the Swing library, which displays standard dialogs. In ZK, you can use org.zkoss.zul.MessageBox for this purpose. It is especially helpful in web programming because it lets you mix program logic with basic user interaction. Anyone who wants to ask for confirmation of a current operation after checking some conditions in business logic will appreciate this functionality. At the end of the example code handling the onClick event, there is a redirection to another page (in this case, to force refresh, it is the same page). Here, I use a static sendRedirect method of the org.zkoss.zk.ui.Executions class, which is analogous to sendRedirect from javax.servlet.http.HttpServletResponse. Figure 2: Example MDI interface in ZK. Figure 3: Table with buttons embedded in its cells. Tables, Nested Controls, and Dynamic Content By defining a model, you make the ZK table responsible for visualization. In this case, however, you can’t specify in ZUL which controls you want to use. ZK can still help with a technique that defines a custom renderer of the table rows view (Listing Ten, available online). The method render of class zkdemo.ui.view.GridRowRenderer is responsible for typesetting an individual table row. For that purpose, it must create child components for the org.zkoss.zul.Row object, which visualizes cells in this row. In the example program, this takes place in the beginning of this method, where labels are created inside a for loop. The rest of the method creates an additional button together with its ON_CLICK event handler. To complete the example, you only need the ZUL table that will set the type of its rows (Listing Eleven, available online). In this example, I also used an alternative method for building a UI in ZK, based on a specialized API. For every ZUL tag, there is a corresponding class with properties that reflect the tag attributes, making it possible to create whole pages in Java alone. Sometimes, this technique offers more flexibility than using XML. Your Own ZUL Components JSP technology lets you define custom tags by writing JSP fragments in a separated file. In a similar way, you can create new ZUL February 2008 l www.ddj.com l Dr. Dobb’s Journal 63 http://www.leadtools.com/dobbs http://www.leadtools.com/dobbs http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - February 2008

Dr. Dobb's Journal - February 2008 Contents Hmmmm Alia Vox Developer Diaries Developer’s Notebook South American Software Development Conversations Inside Visual Studio 2008 BibPort: Creating Bibliographic References Continuous LINQ The ZK Framework Static Testing C++ Code The Agile Edge Effective Concurrency Swaine’s Flames

Dr. Dobb's Journal - February 2008

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