[Dev] User Interface

[David Hyatt]

Curt Hibbs wrote:
 >
 > The are some additional drawbacks to XUL that aren't apparent until 
you have
 > developed a significant XUL code-base. I spent a year and half 
developing a
 > very large, commercial application based on XUL. Initially, XUL 
seemed to be
 > a very attractive solution (and I believe that it still is for small
 > applications). However, the way that the behavior of an XUL 
application is
 > mixed with UI layout specification makes it very challenging to 
maintain
 > clean, understandable code. Consequently, the level of development 
effort
 > was much higher than I had expected.

This is untrue.  The behavior of a XUL application can be kept entirely 
separate from the XML file that describes the layout of the user 
interface.  In fact you have numerous paths that you can follow to 
achieve this separation.

While it is true that XUL supports the mixing of behavior and layout in 
order to make it more accessible to HTML developers, that doesn't mean 
you have to write your XUL files that way.

Here are some sample approaches that you could take to keep behavior 
separate from the XML file.

(1) Use an external script file included from the XML document.  This 
script file could use the DOM addEventListener API to register JS 
functions as listeners on the various elements.  This keeps all of the 
JS code out of the XML file.

(2) Do the same thing as (1), but in C++.  Listeners could be attached 
dynamically in response to the "load" event of the XUL document (or 
earlier should you desire).

(3) Using stylesheets and XBL you can attach bindings to the elements 
via CSS.  Since XBL can specify event handlers, you could perform the 
linkage this way.  (This would allow you to use CSS's selector 
mechanism to attach the same event handlers to whole classes of 
elements).

(4) You could use dynamic overlays and hold your behavior in a separate 
chrome package that can be dynamically superimposed onto the XUL 
structure (or the overlay could just use scripts and follow an approach 
similar to (1)).

There are plenty of easy solutions to this problem.

dave
(hyatt at apple.com)