QML ListView does not reflect updates from its C++ data model [Solved]

p3c0

Hi,

my_data.clear() will just clear the list but you will the view to be notified about the changes. This can be done by wrapping it up in "beginResetModel":http://doc.qt.io/qt-5/qabstractitemmodel.html#beginResetModel and endResetModel:
@
beginResetModel();
my_data.clear();
endResetModel();
@

kwisatz

I just tried inserting that, and my Application Crashed as soon as that code was invoked. Narrowed it down to endResetModel() being the culprit.

ondrejandrej

This code works for me:
@ emit layoutAboutToBeChanged();
my_data.clear();
emit layoutChanged();@

kwisatz

So, with this the Application no longer crashes but my view still seems to hold the model item's in it's view but the I'm not able to scroll between the items.

[quote author="ondrejandrej" date="1421854871"]This code works for me:
@ emit layoutAboutToBeChanged();
my_data.clear();
emit layoutChanged();@[/quote]

As an aside, it'd be nice to find a complete example of a c++ model and a qml view where items are added and removed dynamically but I'm not able to find one online. I'd really appreciate if someone could link it for me.

ondrejandrej

You are creating a model, but it goes out of scope immediately after constructor terminates (I suppose your last code snippet is in a constructor).

You should ensure that the model remains in existence while the QML view is showing, e. g. by allocating on heap:
@MyDataModel *myDataModel = new MyDataModel(this);
context->setContextProperty("myDataModel", myDataModel);@

kwisatz

I've tried to allocate it at the heap as well and the ui remains unchanged. Originally, myDatamodel was a private member of its parent's class. The code snippet was modified to simplify my question.

ondrejandrej

You are using "it's" wrongly. Have a look at http://www.elearnenglishlanguage.com/blog/english-mistakes/its/ . You have it also in the title.

kwisatz

:D Thanks for pointing that out!

p3c0

bq. I just tried inserting that, and my Application Crashed as soon as that code was invoked. Narrowed it down to endResetModel() being the culprit.

I have been using this approach in all my projects where ListView is used. It worked all the time.
Why are you using QDeclarativeView ? Aren't you using Qt 5 ?

ondrejandrej

[quote author="kwisatz" date="1421877712"]:D Thanks for pointing that out!
[/quote]
It's good that you fixed it :D

kwisatz

Sorry, should have made this clear earlier on, I'm using Qt 4.8.4.

[quote author="p3c0" date="1421902494"]bq. I just tried inserting that, and my Application Crashed as soon as that code was invoked. Narrowed it down to endResetModel() being the culprit.

I have been using this approach in all my projects where ListView is used. It worked all the time.
Why are you using QDeclarativeView ? Aren't you using Qt 5 ?[/quote]

p3c0

Well then I'm not sure why it crashes. Qt 4.8.4 still is quite old in Qt4 series. Can you try it on Qt 4.8.6 ?

kwisatz

I've tried this with 4.8.6 but to no avail

At the moment, I'm unable to move to Qt5. I'm cross-compiling for an Embedded Linux System as well, there's a fair amount of porting involved to move to Qt5.

kwisatz

Okay, I did manage to get this to work finally.

When clearing data, I used:
@ beginResetModel();
m_data.clear();
endResetModel();@

When removing an individual item in the data, I used:

@ beginRemoveRows(QModelIndex(), index, index);
m_data.removeAt(index);
endRemoveRows();@

And I worked on this bit of code separately from my main application. Will have to see what kind of fun awaits when I merge the changes with the rest of the application ;)

Appreciate the help folks!