Save List of PropertyBusinessObjects to the Storage - codenameone

Question

I need to save a dinamic List of PropertyBusinessObjects to the Storage, but I didn't find how to do that. I should be able to add and remove items from the list.
The following test code throws java.io.IOException: Object type not supported: CollectiveDAO. I use registerExternalizable().
public class TestSaveListDAOs {
private Form current;
private Resources theme;
public static List<CollectiveDAO> collectivesDB = new ArrayList<>();
public void init(Object context) {
[...]
}
public void start() {
if(current != null){
current.show();
return;
}
Form hi = new Form("Hi World", BoxLayout.y());
hi.add(new Label("Hi World"));
hi.show();
restoreDB();
collectivesDB.add(new CollectiveDAO());
collectivesDB.add(new CollectiveDAO());
saveDB();
restoreDB();
}
public void stop() {
[...]
}
public void destroy() {
}
public static void saveDB() {
for (CollectiveDAO collectiveDAO : collectivesDB) {
collectiveDAO.getPropertyIndex().registerExternalizable();
}
Storage.getInstance().writeObject("CollectivesDB", collectivesDB);
}
private static void restoreDB() {
Object restoredCollectivesDB = Storage.getInstance().readObject("CollectivesDB");
if (restoredCollectivesDB != null) {
collectivesDB = ((List) restoredCollectivesDB);
}
}
}
public class CollectiveDAO implements PropertyBusinessObject {
public final Property<String, CollectiveDAO> collectiveID = new Property<>("collectiveID");
private final PropertyIndex idx = new PropertyIndex(this, "CollectiveDAO",
collectiveID);
#Override
public PropertyIndex getPropertyIndex() {
return idx;
}
}

Answer 1

I'd use JSON rather than Externalizable such as:
public static void saveDB() {
PropertyIndex.storeJSONList("CollectivesDB", collectivesDB);
}
private static void restoreDB() {
collectivesDB = new CollectiveDAO().getPropertyIndex().loadJSONList("CollectivesDB");
}
It's shorter with nicer output. However, if you want to use Externalizable your usage is incorrect. You should remove the for call and instead do:
public void init(Object context) {
new CollectiveDAO().getPropertyIndex().registerExternalizable();
[...]
}
This is needed only once for reading and writing (it was missing for reading). As it registers the new object type (CollectiveDAO).