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By Root 1565 0

to create and maintain. On the programming side, the system needs to be able to call into your application when an Apple event arrives, so as your application starts up it must register the appropriate functions with the Apple Event Manager, and when an Apple event arrives, your code must parse it (no mean feat, especially if it involves a reference to an object in your application) and respond appropriately.

For this reason, programmers have often relied on sample code and application frameworks for assistance in making an application scriptable. There was some concern among programmers, therefore, when Mac OS X first emerged, over how it would be possible to take advantage of the Cocoa application framework and make an application scriptable at the same time. Since those early days, support for scriptability has gradually been folded into Cocoa; this is called Cocoa scripting . Cocoa scripting is still not perfect, but at least it has passed its infancy, and in Tiger it is easier than ever, thanks in part to the introduction of the sdef-based dictionary.

Thus, if you're a Cocoa programmer, Cocoa scripting in Tiger is a good way to start adding scriptability to your application. Getting started is the hardest part, though, for several reasons:

Multiple workplaces

You have to coordinate the sdef dictionary with your code. If you make a mistake in either of them, or if you cause one of them not to match the other, some aspect of scriptability can fail mysteriously.

Scattered documentation

The documentation is copious, but it's scattered in many different places, and elementary tasks and common problems are often not explained clearly. Also, Cocoa scripting uses "key-value coding," which means that often there is no way to look up a troublesome method in the documentation (because it isn't documented, except as a kind of template).

Tiresome testing

Testing is tedious and difficult. Basically, you have to test by scripting your application; you must think of everything an end user might say with AppleScript to your application, and see whether your application responds coherently.

To help you get started with Cocoa scripting, here's a tutorial that adds the rudiments of scriptability to an existing Cocoa application, a little bit at a time. In order to make the example useful, this scriptability will include elements, properties, an enumeration, and a command. I'll assume you're using Tiger for development, and our example application will be scriptable on Tiger only; once you've achieved Tiger scriptability, it is possible to extend your scriptability to work on earlier systems (I'll talk about how to do that in the next section, "AppleScript Studio Scriptability").

Our Cocoa application, which is called Pairs, is very simple. We have a Person class, and we can create multiple instances of it. A Person has a name. Two Person instances can be paired, and this works like a monogamous marriage: once a Person is united to another, it can't be united to any other Person. The application presumably has some sort of interface, but I'm not going to concern myself with that. We assume that the application's basic functionality is working, and that it initializes itself on startup into some useful state—for example, it creates two initial Persons, named "Jack" and "Jill"—and now we want to go back and make it scriptable.

Here's the structure of the application before we start adding scriptability. The main controller class, instantiated in the nib, is MyObject. Here is its interface:

@interface MyObject : NSObject

{

NSMutableArray* persons;

NSMutableArray* pairs;

// outlets go here

}

// method declarations go here

@end

The persons mutable array is made up of Person objects; each Person instance, as it is created, is added to this array. Here is the interface for Person:

@class Pair;

@interface Person : NSObject {

NSString* name;

Pair* pair;

}

- (NSString *)name;

- (void)setName:(NSString *)aName;

- (Pair *)pair;

- (void)setPair:(Pair *)aPair;

// other method declarations go here

@end

As you