App Designer-Tag in event is empty; Value of Listbox is not order

First quesiton is that, I found the 'event' parameter which is the input of callbacks, is containing lots of Object's information, but the 'event.Source.Tag' is empty all the time. If so, how can Callback get the current Object I operate? I know in GUI, every Callback has the input parameter 'hObject' to use, that's convinent. What should I do in App Designer?

Second question is that, in App Designer, the 'Value' of Listbox is not same as in GUI. In GUI,it's an order number of selected item. However in AD, it's item itself (or itemdata itself).If I want to get order number, I have to make itemdata become order series 1,2,3... I think it's not a satisfying method. Then, what should I do? (I need this order number because that in my app every item is corresponding to a matrix. For example, item1 - matrix(:,:,1), item2 - matrix(:,:,2)... When I select an item, the corresponding matrix should be displayed in app. So, the order of selected item need to be acquired).

[Adam]

Do your objects have a tag (in the actual GUI layout, I mean, not in the callback)?

[Chong Cao]

In GUI, I surely knows what tag is. But I'm not sure this 'Tag' in AD means what. Is 'edit' the tag of 'app.edit' in AD? If so, every object must have a tag I think.

Answer 1

[Jurgens Wolfaardt]

For first question: Pre-assign a descriptive Tag to each your objects (in a startupFcn) with the following code:

            FieldNames = fieldnames(app);
            for i = 1:length(FieldNames)
                app.(FieldNames{i}).Tag = FieldNames{i};
            end

Now use strcmp (or similar) to compare the object's event.Source.Tag to determine the function that called it.

Second question answered here: https://au.mathworks.com/matlabcentral/answers/415730-app-designer-listbox-and-dropdown-selection-number#answer_333978

[Chong Cao]

Great！I've found a method,but your method is much more convenient to tag all field. Thanks. For these 1.5 years, I've got a lot progress and write some big apps for my engineering work. I have to say, writting apps is lonely, almost every signle problem needs to be study, and hundreds of them are coming over to me with no ends……