If you're running a data catalog extension where most/all of the objects in the library depend on data catalogs, it can be dangerous to place these objects before the .db3 file has been downloaded. Instead of having a check in each snapper, it's easier to suppress the library from showing anything until at least the database has finished loading.

1. Make a hook that whenever a catalog is loaded, calls updateLibAfterNewDB().
   In extension.cm:

   /**
    * Extension. 
    */
   public class GenericCatalogExtension extends SimpleCatalogExtension {
       /**
        * Initialize.
        */
       public void initialize(ExtensionEnv env) {
           super(env);
           registerDsEmbeddedCatalog(genericCatalogNumber, "GenericCatalogName", {"GenericCatalogName"}); 
       }
   
       
       /**
        * Start.
        */
       public void start(ExtensionEnv env) {
           //register the catalog, may be done somewhere else
           newDataCatalogHooks << function updateLibAfterNewDB; //this hook will be called whenever a catalog has finished downloading
           super(env);
       }
   }

    

2. Rebuild the toolbox when the specific catalog has finished downloading. Also, when you re-open CET it will notice the catalog has already been loaded.
   In library.cm:

   /**
    * A new catalog db has been retrieved, update lib accordingly
    */
   package void updateLibAfterNewDB(CtlgBrwsrCatalogs cats) {
       if (cats and cats._key == "GenericCatalogName") {
           library = null;
           genericRebuildToolboxes("#custom.generic.productLine");
       }
   }
   
   
   /**
    * Generic toolbox rebuild function.
    */
   public void genericRebuildToolboxes(str pkg, World world=null) {
       if (application.toolbox) {
           for (card in application.toolbox.childWindows) {
               if (card as LazyLibraryCard) {
                   if (card.libraryFunctionPkg.toS.beginsWith(pkg)) {
                       card.requestLazyRebuild(true);
                   }
               }
           }
       }
   }

    

3. Check to see if the catalog is loaded. If it's loaded, use the regular library. If not, load a library that tells the user the data isn't ready yet but will refresh when the data is loaded.

   /**
    * Catalog is loaded?
    */
   private bool catalogLoaded = false;
   
   public Library genericLibrary() {
       if (!catalogLoaded) {
           catalogLoaded = ctlgBrwsrCatalogs(genericCatalogNumber, "GenericCatalogName") != null;
       }
       if (catalogLoaded) return genericLoadedLibrary();
       return genericUnloadedLibrary();
   }
   
   
   public Library genericLoadedLibrary() {
       if (developMode) library = null;
       if (!library) {
           symbol pkg = (#:package);
           Library lib = library(pkg=pkg) {
               container LibraryLimb root("GenericFlapHeader") {
                    //Put all the library icons here!!
               }
           };
           library = lib;
       }
       return library;
   }
   
   public Library genericUnloadedLibrary() {
       if (developMode) library = null;
       if (!library) {
           symbol pkg = (#:package);
           Library lib = library(pkg=pkg) {
               container LibraryLimb root("GenericFlapHeader") {
                   limb HeaderLimb txt("genericLoading", image=genericIcon("genericLoadingMessage"));
               }
           };
           library = lib;
       }
       return library;
   }