[CS3][JS][ScriptUI] Observing changes to user selection (advanced)

Question

I have a simple ScruitUI palette working in InDesign which displays the area of a selected page item.
When the user selects a page item and launches the palette the area is calculated and the palette displays the result correctly.
I cannot work out, however, how to update the calculated area when the user changes the selection. I can use the onMove and onResize events on the palette window to trigger the recalculation, but I would like another way that did not involve the user moving or re-sizing the palette. Something like onActive so that all the user had to do was click on the palette to trigger a recalculation.
The simple way out is to create a button on the palette which the user clicks to update the area information, and this may be the best I can do at the moment. I was just wondering if any of the experts had some insight into other techniques for observing changes to selection from a palette. It would be amazing to have a scripted observer that could change the palette without the user doing anything special, in the same way that InDesign panels (like Info) work, but I realize I'm asking a lot from a scripting DOM that is already amazingly comprehensive.

Answer 1

Hi Kasyan,
Below roughly what I sent to Simon - it is not a full solution, but demonstrates the techniques you need.
With APIDToolAssistant installed and a document open, create a page item on the pasteboard; this page item will be used as a 'controller' for this demo. Select it and bring up the APID ToolAssistant palette.
Set the list of subjects to "*"
Set the event filter to "subjectSelected#myLittlePaletteEngine, subjectDeselected#myLittlePaletteEngine".
This captures the selection and deselection events for all page items, and routes them into a persistent engine (myLittlePaletteEngine) for handling.
Because the engine is persistent, it will 'remember' gPalette and gField on subsequent events after they have been created the first time around.
Set the script to:
var gPalette;
var gField;
var gController = theItem;
function CreatePalette()
gPalette =
new Window(
"palette",
"What is it");
gField = gPalette.add("statictext",[0,0,200,20],"testfield");
if (gPalette == undefined)
gController.setDataStore("$GROUP_EVENTS$",true);
CreatePalette();
gPalette.show();
gField.text = app.selection.toString();
This does work for 'page item' selections - it won't work for text selections. To make that work too, you need to change the event filter to "*#myLittlePaletteEngine" (* is a wildcard and matches all events, including idle - which is used to update the text selection info).
This last method (relying on idle) is not terribly good or efficient; I am currently looking how I could avoid the need for capturing 'idle' in version 1.0.46 (which will support CS4).