Triggering common actions for a data model from a view

elfring · 9 Dec 2018, 10:08

I have read the documentation for the topic “Model/view programming” several times.
The data model should support also the following actions at least.

Reloading of needed data
Storing data in a selected format

I have got understanding difficulties to trigger such actions directly by a programming interface which is supported by a class like “QTreeView”.

May views call member functions from their models directly?
Do models need to connect to any signals (or events) for the desired data processing?

I wonder why it seems to be harder than expected to find existing small Qt examples for this use case.

VRonin · 14 Sept 2018, 20:30

Hi, I wrote a library to serialise models in binary, xml, csv and json. You can find it here referred as "Model Serialisation". it's not fully documented (hence the dev branch) but you can find an example usage here

Don't know if the questions are related to the above but I'll answer

May views call member functions from their models directly?

They may and they do

Do models need to connect to any signals (or events) for the desired data processing?

A bit to generic of a question. depends on the data processing

elfring · 12 Sept 2018, 11:53

May views call member functions from their models directly?
They may and they do

Thanks for your quick answer.

It seems that I have overlooked the useful function “QAbstractItemView::model()”.

JonB · wrote on 12 Sept 2018, 11:53

@elfring
That function gives the model the view is attached to. From that you can obviously do whatever you fancy on the associated model. Is that what you mean you did not know existed, and so you thought the view could not access the model?

elfring · wrote on 12 Sept 2018, 12:32

Is that what you mean you did not know existed,

It seems so.

and so you thought the view could not access the model?

I needed another moment to recognise this way to get access to the desired model object.

elfring · 15 Sept 2018, 17:35

A bit to generic of a question.

How do you think about to discuss any more meaningful application examples?

mrjj · 15 Sept 2018, 17:56

@elfring
Well to change the internal structure of cppcheck to use models in the
intended way would be a benefit but to change GUI to QML would not
in my opinion not bring anything worthwhile besides huge amount of new code to let
QML access the data. However, it would ensure a very good separation
between data and presentation as there is no shortcuts
interfacing QML with c++ backbone models.
However, cppcheck needs neither animation or hardware accelerated drawing so
its hard to see what the gain would be. ( compared to the extra work of using QML)

elfring · 17 Sept 2018, 15:52

hi

Will the support change for UI and QML file formats over time?
Well QWidgets are very stable and its very unlikely that UI format will radically change.
QML is more of a work in progress so it could happen that very old QML file would require some
minor changes to load in brand new Qt but given the history of avoiding breaking
even binary comparability, its not likely to be a real world issue.
Would you like to help any more with the separation of data structures for models and views?
If you mean outside of answering question here in forum, then no thank you. :)

elfring · wrote on 17 Sept 2018, 15:52

If you mean outside of answering question here in forum, then no thank you. :)

I am curious then if you would like to clarify related development topics.

Do you know any higher level tools which can display structural differences between standard item models in a clear way?
Have you got any experiences with “diff views” in this software area?