October 31, 2014
 
 
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Borland's Kylix: turbocharging Linux development - page 3

Not Your Father's TurboPascal

  • April 9, 2001
  • By Scott Courtney
Less intuitive, at first, was the creation of a main menu and a toolbar. Kylix has abstracted the concept of an Action List, which contains all of the user-driven action events that can be handled by the form. Instead of defining the menus and toolbars, and then filling in their behaviors (the actions) later, Kylix makes you define the comprehensive list of actions first and then attach them to toolbars or menus. This was counter-intuitive to me, but once I realized what Kylix expected I had no difficulty completing the task. Likewise, the little button images (mini-icons) used for the dropdown menus and toolbars are drawn from an Image List which is created before the menus and toolbars that use it. In this process, I found a Kylix bug: You are supposed to be able to re-order the images by dragging them around in the Image List, but I was totally unable to get this feature to work except for moving one image, one time. I am not sure why it worked once, but I was unable to make it work again. This was upsetting to my sense of order that wanted the images to be inside the Image List in the same order they appeared on the menus of my application. Practically speaking, though, it had no effect because each Action List item has an integer index into the Image List, and these can be in any arbitrary order.

Once you have defined the Action List and (if desired) the Image List, creation of the application's main menu is extremely easy, and consists only of selecting the blank spaces on the menu and using the context popup menu to add a new item, then editing its properties to point to the appropriate action. Creating a toolbar is equally easy and involves much the same process.

Finally! Some Actual Code!

Once I had the GUI defined, it was time to attach real code to the event handlers. Kylix uses an object-oriented event model in which the very act of calling a particular function on a particular object instance implies which object receives the event and which event type is being received. This is similar to the event model in Java 1.1 and later, although the notion of an event as an object in and of itself is downplayed. In any event (pun intended), the model used in Kylix and Java alike is much more elegant than the old "case statement from hell" approach used in the days of Windows 3.x.

Some of the trickiest operations needed by the text editor application are also pre-built for you. Kylix includes a selection of common actions such as cut, copy, delete, and paste, and these can be attached easily to menu items. Additional code required for clipboard functions: zero.

For the rest of the functions, most notably the File... menu, the code was simple and straightforward, and typical of what is used in just about any GUI environment. At various points in the coding, a little code-completion menu will pop up and offer a fairly intelligent listing of the possible completions of the current syntactic token. For example, after you have typed the name of an object instance, the popup will show the method (function) names that apply to that object. As you type the first few letters, the choices narrow further and further. At any time, you can use the keyboard or the mouse to select the one you want. Parameter help is also included.

The File...Open dialog is trivial, because it simply invokes a standard dialog operation (modal) and then reads the result to see if the user actually chose a file. I did find a bug in this function: If you add an option of "all files" (for file type) and have a mask of "*", it fails to match anything. Apparently Borland has introduced a DOS-ism here in that they assume every file will match "*.*" and not "*" by itself. Hopefully this will be fixed in the next release, but for now it is an annoyance.

The Help...About dialog is also trivial to implement, if you don't want anything fancy. I was pleasantly surprised to note that a fixed- text label that exceeds one line automatically wraps, something that some IDEs do not handle gracefully.

At this stage, I had a working text editor! All the basic clipboard and text selection features worked as expected. Help...About did what it was supposed to do, and behaved modally as is typical. Except for the filename masking bug previously mentioned, File...Open also worked as intended and text files (.txt extension) opened perfectly. It was interesting to note that there were, by default, no scroll bars in the text editing area, but the PgUp, PgDn, and arrow keys allowed navigation. I am sure that adding the scrollbars is simply a detail I overlooked, perhaps only a matter of setting the right properties on the text area itself.

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