Creating GUI is no easy task. But creating GUI creators is a even more complex task. Almost a nightmare. But the long road walked by GUI creation programs, we already know somethings that are good and somethings that are bad.
Quite a long time, desktop IDE’s acknowledged that letting developers to create GUI with some kind of drag and drop interface were critical. That were because GUI were less and less created by programmers but more and more by designers, that have little knowledge and patience to deal with programming code. It also facilitate the adoption by beginners.
A too designer/beginner driven interface for creating GUI might also not be a good choice. The whole customization and generalization possible by programming is lost. Its too case-by-case development. Its not cost efficient. That’s why a middle term is needed. Some kind a language that is easy enough for designers but programmable. Drupal CMS uses the Form API, a PHP array that will be used to create HTML forms. Its quite easy to be used by newbies. I heard that QT is preparing some custom language for creating their UI too.
UPDATE (2010-10-03): Qt revealed QML.
Most GUI element have a fixed set of parameters. But sometimes the GUI should be generated on the fly. Developing GUI like this is very try-and-error. To facilitate the creating phase, its important to be possible to see it working with some generic data.
The UI 101 rule is to separate the data to the layout. But it is important to let the users to chance any of them. For example, the user can enter his birth year by a textfield or a dropdown list, or some nice JS calendar. This example show how to change the widget, the GUI element. However, the user might need to change the data type. If the birth year was originally text, the user might decide to change it to integer number. The challenge here is to convert saved data. But for most cases, it is feasible.
Developers of both desktop and internet applications are experiencing a quite interesting phenomenon: the same application must have several outputs, like netbook version or mobile sites. With the rise of HTML5, sites now might need multiple different outputs. Also, we must have different outputs when we are creating, viewing or update content. The concept of multiple contexts might be anticipated by the GUI creators.
Integers, float numbers, strings… all developers know these data types. But they know that in some cases it is needed a more complex data types; combination of primitives. Some programming languages have structures and objects to address this idea. But GUIs can also be the combination of multiple primitives. Imagine a “password_checker” GUI element that is, in fact, two form fields that will check if the user typed the password correctly or an “address” element that is in fact a group of *country, province and city* fields. Users might be enabled to create and edit these type of custom data structures.
UPDATE (2009-10-05): I just saw a issue posted against CCK module called State of the multigroup module. It has close relationship with this post. Curious is that it is more a hack than a core idea.