Edit AllPages

An AppleScript command’s target depends on its direct parameter. The direct parameter can be a constant or an application-provided object. A parameter like third word of “do re mi fa” is a constant, but a parameter like name of application is an application-provided object, though they are both string values. If the command’s direct parameter is a constant, then the command’s target will be the nearest enclosing tell block, but if it is an application-provided object, it will be that object.

As an example, say you implement a “send” command whose direct parameter should be a string but whose target should be a “network connection” class. In the script tell network connection 1 to send “Hello” the target of the send command will be network connection 1, the enclosing tell block, because “Hello” is a constant. However, in the script tell network connection 1 to send name of application the target of the send command will be name of application, not network connection 1, because name of application is an application-provided object, not a constant.

You can see the problem. In the second script, the send command won’t know which network connection the message should be sent out on.

A solution is possible, but not by default. Apple Events can have a subject attribute, accessed by the attribute key ‘subj’. Normally, this attribute only shows up when the direct parameter is a constant, in which case it is set to the nearest tell block. But if the direct parameter is an application-provided object, the nearest tell block is ignored and this attribute doesn’t appear.

You can tell AppleScript to always provide the subject attribute regardless. You can then rely on the subject attribute, or perhaps an optional “to” parameter of the command, to determine the real target. I say “real target”, because CocoaScripting will think the direct parameter is the real target.

To force AppleScript to always include the subject attribute, add a ‘scsz’ Resource Manager resource to your application. The resource should have the alwaysSendSubject bit set. Here is a .r file that can do this, to be included in a Resource Manager build phase:

#include <Carbon/Carbon.r>

resource ‘scsz’ (0, “Scripting Size”, purgeable) { dontLaunchToGetTerminology, findAppBySignature, alwaysSendSubject, reserved, reserved, reserved, reserved, reserved, reserved, reserved, reserved, reserved, reserved, reserved, reserved, reserved, minStackSize, preferredStackSize, maxStackSize, minHeapSize, preferredHeapSize, maxHeapSize };

You will need to be able to evaluate the ‘subj’ attribute. Here is a category function on NSScriptCommand that can do it:

If the scripter happens to pass in an application-provided object as the direct parameter, you’ll need to evaluate it, because the NSScriptCommand’s directParameter method won’t. Here is another category function:

Finally, you should add the appropriate tag and the tag to [[NSCoreSuite's "item" class. Remember that CocoaScripting will not know that the direct parameter can't be used to determine the target of this command. Adding the command to the "item" class makes *any* direct parameter a valid target for the command, since all AppleScript classes inherit from "item".


Updated the “subjectsSpecifier” code, because I found that calling _objectSpecifierFromDescriptor with a nil argument set an error flag in the AppleEvent currently being handled (tested on Leopard). This was causing Colloquy to return an error when I was sending AppleEvents to it.


On Leopard, you can use the newly-public method +[NSScriptObjectSpecifier objectSpecifierWithDescriptor:] instead of _objectSpecifierFromDescriptor. It still fails and sets an error on your script execution context if you give it nil or @’null’, though.