Java™ Application Development on Linux - Dator

17.3 Porting BudgetPro to SWT391the separate create-then-add semantics used in the original will not apply. Inthe next section, we will walk through converting one of these three createmethods. For now, it is enough to know that they will be changed to be methodsthat return void (no return value) and the calls to add() may be deleted.That completes the conversion of main().17.3.3 Step 3: Converting the GUI build() and init()MethodsLest you believe that this means the application is ready to run, just trycompiling what you have. Got a few errors yet, don’t we?Let’s walk through converting the createStatus() method and its relatedmethods. We’ll then briefly discuss converting the createList() andcreateButtons() concentrating on the details of the unique UI widgets usedin each.17.3.3.1 Converting the GUI build() MethodIn BudgetPro, the top part of the UI is the status pane. It consists, basically, ofthree labels. In the original application, this pane is constructed by thecreateStatus() method. In the original, it returns a Swing Component,which is then placed by calling add() on a container managed by the caller.In SWT, Widgets must be joined to their containers at construction, so wemust restructure this code a little bit. We create a Group to hold our classestogether as a unit. We attach the group directly to the parent Shell by usingthe member variable frame. We set the layout manager to be RowLayout.We then populate the Group. First, we add the Up button, which is onlyenabled when in a subaccount. While SWT does support image buttons, wetake the shortcut of using the SWT.ARROW style, bitwise-or’ed with the SWT.UPstyle. Next, we populate the group with our Labels.Note a change we will talk about some more below: The listener forthe Button object called upton is changed. The method is renamed fromaddActionListener() to addSelectionListener(). Event handling inSWT is similar to Swing/AWT, but not identical, as we will see when we goover the rewrite of the actual event handler code a little later on.These are the only changes we make to this method.