Storing per project script data ?

Question

Hello,
I have configuration for user selections that I need to store on a per project basis, things like files paths and co.
Where this data should be kept, I obviosuly can keep it in a seperate file next to the psd, or inside photoshop registry but I'm looking for a better solution of storing the data inside the psd file itself.
Is there an API solution for this, or should I be looking into hacks such as finding an unused XMP field and storing the data there?
What is important to me is that this data will survive application reboots.
Second priority is the situation that a user emails the psd to someone else, I would like this data to be present there as well.
Any suggestions?

Answer 1

Unless Xbytor knows something about layers that I don't I think when he said 'a hidden text layer' he meant a normal text layer with the visibility turned off. The layer would still be in the layers panel.
I am not sure what you mean by 'CompsLayer'. If you mean Layer Comps, then no layer comps are not layers so don't have layer metadata.
Here is an example of using reading/writing layer metadata.
loadXMPLibrary();
try{
var layerXMP = new XMPMeta( activeDocument.activeLayer.xmpMetadata.rawData );// get the object
}catch(e){
    var layerXMP = new XMPMeta();// layer did not have metadata so create new
var lastUpdated = getLayerChangedDate();// get the date. Photoshop updates time so no need to set.
setDescMetadata( 'Desc' );// set desc
var comment = layerXMP.getProperty( XMPConst.NS_EXIF, "userComment" );// get comment
var count = layerXMP.countArrayItems( XMPConst.NS_DC, "description"  );// get the number of items
if ( count == 0 ) {
    layerXMP.getArrayItem( XMPConst.NS_DC, "description", 1 );
setCommMetadata('comment');// set comment
lastUpdated = getLayerChangedDate();// get the date. Photoshop updates time so no need to set.
alert(lastUpdated);
unloadXMPLibrary();
// these function adapted from PerLayerMetdata.jsx -Copyright 2008 Adobe Systems Incorporated
// to use these functions are from the Photoshop Panel Developer's Guide.
function loadXMPLibrary(){
    if ( !ExternalObject.AdobeXMPScript ){
        try{
            ExternalObject.AdobeXMPScript = new ExternalObject('lib:AdobeXMPScript');
        }catch (e){
            alert("Can't load XMP Script Library");
            return false;
    return true;
    The function unloads the XMP Script Library.
function unloadXMPLibrary(){
    if( ExternalObject.AdobeXMPScript ) {
        try{
            ExternalObject.AdobeXMPScript.unload();
            ExternalObject.AdobeXMPScript = undefined;
        }catch (e){
            alert("Can't unload XMP Script Library");
function setDescMetadata(desc){
    if( app.activeDocument.activeLayer.isBackgroundLayer ){
        alert( 'Can not place metadata on a background layer.');
    } else {
        var xmp;
        if (desc == "")
            desc = " ";
        try{
            xmp = new XMPMeta( app.activeDocument.activeLayer.xmpMetadata.rawData );
        } catch( e ) {
            xmp = new XMPMeta();
        try{
            if( xmp.countArrayItems( XMPConst.NS_DC, "description" ) == 0 ){
                xmp.appendArrayItem( XMPConst.NS_DC, "description", null, XMPConst.PROP_IS_ARRAY, XMPConst.ARRAY_IS_ORDERED );
                xmp.insertArrayItem( XMPConst.NS_DC, "description", 1, desc );
            } else {
                xmp.setArrayItem( XMPConst.NS_DC, "description", 1, desc );
        } catch( e ) {
            alert( 'Unable to place description metadata on selected layer.\n' + e );
        app.activeDocument.activeLayer.xmpMetadata.rawData = xmp.serialize();
function setCommMetadata(comm){
    if( app.activeDocument.activeLayer.isBackgroundLayer){
        alert( 'Can not place metadata on a background layer.' );
    } else {
        var xmp;
        if ( comm == "" )
            comm = " ";
        try{
            xmp = new XMPMeta( app.activeDocument.activeLayer.xmpMetadata.rawData );
        } catch( e ) {
            xmp = new XMPMeta();
        try{
            xmp.setProperty( XMPConst.NS_EXIF, "userComment", comm );
        } catch( e ) {
            alert( 'Unable to place metadata on selected layer.\n' + e );
        app.activeDocument.activeLayer.xmpMetadata.rawData = xmp.serialize();
function getLayerChangedDate(){
    var ref = new ActionReference();
    ref.putProperty( charIDToTypeID( 'Prpr' ), stringIDToTypeID( "metadata" ) );
    ref.putEnumerated( charIDToTypeID("Lyr "), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
    var desc = executeActionGet( ref );
    if ( desc.hasKey( stringIDToTypeID( "metadata" ) ) ){
        desc = executeActionGet( ref ).getObjectValue( stringIDToTypeID( "metadata" ) );
        var timeInSeconds = desc.getDouble( stringIDToTypeID("layerTime") );
        var d = new Date();
        d.setTime( timeInSeconds * 1000.0 );
        return d.toLocaleString();