Volume Number: 15 (1999)
Issue Number: 3
Column Tag: MacTech Online
by Jeff Clites <online@mactech.com>
Make your applications scriptable.
The advice is as simple as that.
The standard reasoning is that by making your application AppleEvent-aware, you make it move valuable - users can automate repetitive tasks and incorporate your product into a larger workflow. Recently I was reading the FAQ for the popular FTP client Anarchie Pro (by Stairways Software). The question on the table was, "Why don't you give Anarchie the ability to repeatedly poll busy FTP sites until it can get in?" The answer was that they don't want to add this feature, because it would be a disservice to the already-busy FTP sites, but you can achieve the same effect using AppleScript. I found this intriguing - not only does scriptability save the authors from having to program in this functionality themselves, but also it allows them to discourage using their product this way, but still allows the user to make the final decision on the matter. That is the gem of scriptability - empowering your users to use your product in ways that you didn't predict.
There's a second, more subtle motivation to making your applications AE-aware - it makes your design better. If you want to make your application extensively scriptable (and recordable), you need to factor it correctly - to separate the UI from the implementation as much as possible. One method for doing this is the Model-View-Controller paradigm, which incidentally is the way most Yellow Box applications are developed. So there's a nice harmony here - factoring your applications to make them scriptable also prepares you for later moving to Yellow Box development, and Yellow Box development is by default done in a manner which makes it trivial to add extensive scripting capabilities to applications.
There are three separate aspects of AppleEvents which might be important to you as a programmer: making your application AppleEvent-aware (your application is an AE-server), controlling other applications with AppleEvents (your application is an AE-client), and writing applications in AppleScript itself. This month we are going to point out some informational resources for each, and next month we'll look at some utilities and libraries to help with the implementation.
The definitive references of course come from Apple. The Interapplication Communication (IAC) section of their Mac OS 8 Developer Documentation provides pointers to the essential publications and technotes, including their AppleScript for Developers page. Another key resource is articles from back-issues of Apple's now-defunct journal develop. They have a page which collects links to all of the IAC articles, and these are also all available in HTML form, complete with accompanying source code, on MacTech's web site. A similar, annotated list is available on Main Event's site. For a printed reference, I highly recommend Dave Mark's Ultimate Mac Programming (ISBN 1-56884-195-7). Don't let its uninformative title fool you - about a third of this thick volume is devoted to getting the developer up to speed with all things AppleEvent-related, and I have yet to find a reference which does a better job of explaining the subject and getting you oriented.
For a glimpse of the future, take a look at the Scripting documentation for Mac OS X Server. Yellow Box applications will get a great deal of scriptability "for free", and it will be easy to extend their scriptability further. Scripting fits nicely with the Yellow Box application model, and promises to have a bright future under Mac OS X later this year.
Included among the develop articles mentioned above are two that I think are key. Ideally you would read all of them, but failing that check out "Programming for Flexibility: The Open Scripting Architecture" which is foundational and really gives you a feel for the power of Apple's scripting architecture, and "According to Script: Attaching and Embedding Scripts" which I hope will sell you on the virtues of this powerful but underutilized technique. (The simplest example is just providing your users with a "scripts" menu.)
Stay tuned for next month, when we'll cover development tools to make your AppleEvent programming a breeze.
These and a bevy of other links are available from the MacTech Online web pages at www.mactech.com/online/.
