ListView: Is there a signal after the list view has been updated?

maxwell31

Hi,

I have a list view which displays a C++ model. After the model is updated (e.g. rows added or removed) I want to use the positionViewAtIndex function the center an item in the listview. To which system should I listen to?

Can I listen to the signals of the model, e.g. endInsertRows? I am aksing because I don't understand the order in which things happen. After the model changed, the list view could need to create new components, so postionViewAtIndex should happen after this happened, right?

eyllanesc

@maxwell31 There are many signals for each type of modification(See https://doc.qt.io/qt-5/qabstractitemmodel.html#signals). A possible solution is that you create a custom class where you create a signal that is connected to the other signals and then use that signal in QML:

class FooModel: public XModel{
// ...

signals:
    void fooSignal();
//...
};

```cpp
// in constructor
connect(this, &FooModel::rowsRemoved, this, &FooModel::fooSignal);
connect(this, &FooModel::rowsInserted, this, &FooModel::fooSignal);
connect(this, &FooModel::modelReset, this, &FooModel::fooSignal);
connect(this, &FooModel::dataChanged, this, &FooModel::fooSignal);
// ...

Then

Connections: {
    target: cppModel
    onFooSignal: function(){
        console.log("Foo");
    }
}

maxwell31

What I meant was rather the following:

Lets assume a model is reset. If I connect to endModelReset, and call positionViewAtIndex, can I be sure, that the ListView already completed constructing the delegates, so that positionViewAtIndex does what it should?

GrecKo

No you can't, since the ListView might not even create the delegates if those are of the view.
However I would assume it to work regardless of this.
You could wrap your positionViewAtIndex call in a Qt.callLater to be sure it's not called too soon.