Feasibility of Firing Custom Events from C++ Plugin and Listening in InDesign UXP Plugin

InDesign
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1

Hello UXP community,

I’m exploring a hybrid plugin approach for Adobe InDesign where we combine a C++ plug-in with a UXP plug-in.

Goal:
From the C++ plug-in, fire a custom event and have the UXP plug-in listen to it via app.addEventListener() in JavaScript.

Background:

  • In CEP, this was possible by dispatching events from C++ using the SDK and catching them in ExtendScript or JavaScript.

  • In UXP, I have successfully called commands and scripted actions, but I have not found documentation confirming whether custom events (not built-in InDesign events) can be dispatched from C++ and picked up in UXP.

  • UXP docs show app.addEventListener(eventName, handler) for built-in events, but it’s unclear if C++ → UXP custom events are supported.

Questions:

  1. Is it technically feasible to dispatch a custom event from a C++ plug-in and listen to it in a UXP plug-in?

  2. If yes, what would be the correct approach or API?

  3. Are there any limitations on event names, payloads, or event types that UXP can handle from the C++ side?

Any insights, examples, or documentation references would be greatly appreciated.

Thanks,
Niraj

2

This technique would be interesting for my team to use to migrate from ExtendScript to UXP. We’d like to get our customers using the UXP-based solution as it slowly gets developed. The ExtendScript-based solution is huge, and we don’t expect to have everything moved over to UXP for another year or so. If we had a way to send a request to ExtendScript, this could get us users sooner. Maybe there’s another way, but I wasn’t aware of any communication options between ExtendScript and UXP because our ExtendScript runs in its own engine.

jsw

3

If your ScriptInfo resource targets kUxpScriptMgrBoss instead of kJavaScriptMgrBoss, or directly kCoreScriptManagerBoss, the constants matching your event names should show at the supported class.

E.g. something similar to

alert(LayoutWindow.AFTER_ACTIVATE);

… assuming you have a working alert(), and using YOUR_EVENT_NAME …

Jon, yours is a different problem.

E.g. here a cheap shim for an UXP alert()

function alert()
{ app.doScript(“alert.apply(this,arguments)”,ScriptLanguage.JAVASCRIPT,[…arguments]); }

4

To specify the targetengine, use the same directive as always.

app.doScript(“#targetengine Jon\n alert($.engineName)”,ScriptLanguage.JAVASCRIPT);

1 Like
5

Thanks, @Dirk. I’ll give that #targetengine concept a test. That might help us out.

Jon

6

@Dirk That concept indeed worked great. Thanks!

Is there a known way to communicate from ExtendScript to a UXP-based plug-in?

And I don’t mean just the result of the .doScript but instead calling something in the UXP-based plug-in from our ExtendScript solution as needed from there.

Jon