In my application, there is a menu (the "Scripts" menu) that is only visible if script files are registered. There is one menu item for each file registered.

Here is the code to create the "Scripts" menu dynamically:

        FileSystem fs = FileUtil.createMemoryFileSystem();
        FileObject fob = null;
        OutputStream fstream = null;
        OutputStreamWriter out = null;
        try {
            fob = fs.getRoot().createData("layer", "xml");
            fstream = fob.getOutputStream();
            out = new OutputStreamWriter(fstream);
            out.write("<filesystem>");
            out.write("    <folder name=\"Menu\">\n"
                    + "        <folder name=\"Scripts\">\n"
                    + "            <attr name=\"position\" intvalue=\"1270\"/>\n"
                    + "            <file name=\"MultiComponent.shadow\">\n"
                    + "                <attr name=\"position\" intvalue=\"100\"/>\n"
                    + "                <attr name=\"originalFile\" stringvalue=\"Actions/Scripts/com-mycompany-core-actions-MultiExecutePythonScriptAction.instance\"/>\n"
                    + "            </file>\n"
                    + "        </folder>\n"
                    + "    </folder>");
            out.write("</filesystem>");

        } catch (IOException ex) {
            logger.log(Level.INFO, "Can't set scripts menu", ex);
            fob = null;
        } finally {
            try {
                if (out != null) {
                    out.close();
                }
            } catch (IOException ex) {
                // Do nothing.
            }
            try {
                if (fstream != null) {
                    fstream.close();
                }
            } catch (IOException ex) {
                // Do nothing.
            }
        }
        if (fob != null) {
            try {
                URL uri = fob.getURL();
                DynamicShowScriptsMenuLayerContent.enable(uri);
                isShown = true;
            } catch (Exception ex) {
                logger.log(Level.INFO, "Can't show scripts menu", ex);
            }
        }
    


public class DynamicShowScriptsMenuLayerContent extends MultiFileSystem {

    private static DynamicShowScriptsMenuLayerContent INSTANCE;
    private static final Logger logger = Logger.getLogger(DynamicShowScriptsMenuLayerContent.class.getName());

    public static void enable(URL url) {
        if (!hasContent()) {
            try {
                XMLFileSystem fileSystem;
                fileSystem = new XMLFileSystem(url);
                INSTANCE.setDelegates(fileSystem);
            } catch (SAXException ex) {
                logger.log(Level.WARNING, "Could not load show scripts menu", ex);
            }
        }
    }

    public DynamicShowScriptsMenuLayerContent() { // called because of declaration in META-INF/services
        // will be created on startup, exactly once
        INSTANCE = this;
        setPropagateMasks(true); // permit *_hidden masks to be used
    }

    public static boolean hasContent() {
        return INSTANCE.getDelegates().length > 0;
    }

    public static void disable() {
        INSTANCE.setDelegates();
    }


The "com.mycompany.core.actions.MultiExecutePythonScriptAction" class extends AbstractAction and implements DynamicMenuContent. It works fine the first few times the "Scripts" menu is open: registered script files are shown as menu items.

However, after a while, it stops showing any valid menu item. The word "Empty" is shown instead. The "DynamicMenuContent.getMenuPresenters" method is not even called. 

It looks like NetBeans realizes after a while that the Scripts menu is not a static menu, and forgets the dynamic registration.

It's important for the Scripts menu to be not visible if users don't have script files registered.

Is it a bug or am I registering my dynamic menu incorrectly ?