InDesign CS5 Script: Why is `#targetengine` not working correctly?

Question

I understand that the declaration #targetengine "myEngineName" would be used for InDesign to remember global variables (found information on this here:  http://incom.org/post/89818).

---

However, this was still not enough for it to remember global variables as it still throws an error regarding the global variable imgs:

Error Number:  30476
Error String:  "if(imgs[i].itemLink != null)" could not be completed because the object no longer exists.

...or something like that anyway. It doesn't like that particular line in my code, and seems to be forgetting what the global variable imgs was instantiated as.

---

So I implemented a try-catch statement, and reinstatiated the variable imgs and decremented the iterator in the catch... Though this did solve the problem, why doesn't #targetengine "myEngineName" solve the problem like it is supposed to?

Here is my code:

#target "InDesign" // this solves the "Error Number: 29446" problem
#targetengine "session" // this solves the "Error Number: 30476" problem

var imgs; // global variable for the #targetengine "session" to keep track of
var document = app.activeDocument;
var newFolder = createFolder(document); // if subdirectory images DNE, create this folder with the function below

saveAllImages(document, newFolder); // with the function below

alert("The file conversion is complete!\n\nAll black & white images have been copied to:\n" + newFolder +
        "\.\n\nAll color images have been replaced with the new black & white images in the current InDesign document.");

//---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

function createFolder(doc)
{
    try
    {
      /*
         * type-casting the filePath property (of type object) into a String type;
         * must be a String type to concatenate with the subdirectory variable (also of type String)
         */
        var docPath = String(doc.filePath);
        var subdirectory = "/BLACK AND WHITE IMAGES";
    }
    catch(e)
    {
        alert(e.message + "\n - reload the script, and it should work.");
        exit();
    }

    var imagesFolder = docPath + subdirectory; // concatenating the two variables
    if(!Folder(imagesFolder).exists)
    {
        Folder(imagesFolder).create();
    }

    return imagesFolder; // for instantiation outside of this function

} // end of function createFolder

//---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

function saveAllImages(doc, folder)
{
    imgs = document.allGraphics; // this is a global variable, for the #targetengine "session" to keep track of
    var fileName = "";
    var img = "";
    var imgType = "";

    for(var i = 0; i < imgs.length; i++)
    {
        try
        {
            if(imgs[i].itemLink != null)
            {
                fileName = imgs[i].itemLink.name;

                img = new File(folder + "/" + fileName); // each image instantiated here
                imgType = imgs[i].imageTypeName; // image type is determined here (.tif, .jpg, .png, etc..)

                //alert("The file \"" + fileName + "\"\n\tis a " + imgType + " file."); // Note: escape characters

               /*
                     * array for image options, instantiated from the function below;
                     * options[0] is the "MAXIMUM" image quality property, &
                     * options[1] is the "GRAY" image conversion property;
                     */
                var options = convertToBlackAndWhite(imgType);

                // each image exported to the new folder here, by file type
                switch(imgType)
                {
                    case "GIF":
                        alert("This script cannot convert and export the GIF file:\n\t" + fileName + " !"); // Note: escape characters
                        break;

                    case "Adobe PDF":
                        break;                            
                    case "EPS":
                        break;
                    case "Windows Bitmap":
                        break;
                    case "JPEG":
                        break;
                    case "PNG":
                        break;
                    case "TIFF":
                        options[0]; // maximum image quality
                        options[1]; // black & white conversion

                        imgs[i].exportFile(ExportFormat.JPG, img, false);
                        replaceWithNewImage(doc, fileName, img); // with the function below
                        break;

                    default:
                        alert("\tUnlisted image type: " + imgType + "!\nAdd this type to the switch statement.");
                        break;
                } // end of switch statement

            } // end of if statement
        } // end of try statement
        catch(e)
        {
            /*
                * in case the #targetengine is overloaded, this solves the "Error Number: 30476" problem:
                *           - "The requested action could not be completed because the object no longer exists."
                *               (the second statement #targetengine "session" is also in place to solve this error)
                */
            imgs = document.allGraphics; // global variable reinstantiated in case of error
            i--; // retry the same iteration again, in case of error (the variable " i " is the iterator in the for loop)
        }
    } // end of for loop

} // end of function saveAllImages

//---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

        function convertToBlackAndWhite(fileType)
        {
            // array for image-quality and color-conversion values
            var settings = [];

            // each image exported to the new folder here, by file type
            switch(fileType)
            {                    
                    case "Windows Bitmap":
                        break;
                    case "JPEG":
                        break;
                    case "PNG":
                        break;
                    case "TIFF":
                    settings[0] = "app.jpegExportPreferences.jpegQuality = JPEGOptionsQuality.MAXIMUM"; // maximum image quality
                    settings[1] = "app.jpegExportPreferences.jpegColorSpace = JpegColorSpaceEnum.GRAY"; // black & white conversion
                    break;

                default:
                    break;
            } // end of switch statement

            return settings; // for instantiation outside of this function

        } // end of function convertToBlackAndWhite

//---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

function replaceWithNewImage(doc, imageName, newImage)
{
    var links = doc.links;
    var link = "";
    for(var i = 0; i < links.length; i++)
    {
        link = links[i];
        if ( (link.status == LinkStatus.NORMAL) && (link.name == imageName) )
        {
            try
            {
                link.relink(newImage);
                link.update();
            }
            catch(e)
            {
            }
        } // end of if statement
    } // end of for loop

} // end of function replaceWithNewImage

This is the only information out there I could find regarding this error:  http://forums.adobe.com/thread/748419

EDIT --

I'm pretty sure the problem has something to do with the function replaceWithNewImage, because this error did not occur without this function, and there was then no need for the try-catch statement...

Rhiana

Answer 1

Reading over your code, I see something that may be really problematic. You set the reference to the document to the active document. But this reference remains all over the session. Fact is if you switch to another document or close the document, then the reference is lost. This may explain why imgs can be undefined at some point although I think it should raise an error instead. Do wrap your variables in a function scope and I warranty you everything will be fine ;)

Octamerous

Interesting... so instead of using app.activeDocument I tried app.documents[0], and this error now does not occur. So it does seem that the variable is becoming undefined because of the app.activeDocument; statement, and that the document changing focus to the images folder could be causing this. Thanks for the help @Loic! – Rhiana

That's why it's good not to use global variables if you can avoid it ;) – Octamerous

Answer 2

First of all, just avoid global variables as much as you can and especially while using session engines.

If the aim of your script is a simple export links/modify links/replace links, why do you want to have persistent variables ?

In my humble opinion, I will get rid of the engine and just do a regular funbction call

//myscript.jsx
mySuperFunction();
function mySuperFunction()
{
    var doc;
    if ( app.documents.length == 0 ){ return; }
    doc = app.activeDocument;
    //Do all your stuff
}

It should be all you need ;)

Loic

Frugivorous

Thanks for the help @Loic! However, I was first using a regular function call as you are suggesting, but the variable imgs becomes undefined, or "no longer exists" for some reason... – Rhiana

I was assuming that the ESTK's main engine was being overloaded, and needed the #targetengine to prevent variables from becoming undefined. Yet, the same problem occurred so I thought that the #targetengine would keep track of global variables... So then after that not working, I just reinstantiated the variable imgs in the catch of the try-catch statment, and it works! And I agree -- I try to avoid global variables, but the info at incom.org/post/89818 seems to suggest that's what a #targetengine is used for... – Rhiana