How to access ListView's current item from qml

Question

I have an application that stores and edits notes. The list of notes is displayed in a listview like this:

Page {
        id: noteList
        title: i18n.tr("QNote")
        visible: false

        Column {
            anchors.fill: parent

            ListView {
                anchors.fill: parent
                model: notes
                delegate: ListItem.Standard {
                    text: Title
                    onClicked: editNote(NoteText, Title, modelData);
                    progression: true
                }
            }
        }
    }

function editNote(text, title, item) {
    pageStack.push(noteEdit, {title: title, text: text});
    handler.setActiveItem(item);
}

The notes item is a NoteListModel that subclasses the QAbstractListModel and contains NoteListItems. What I would like to do is to store the currently selected NoteListItem so I could easily access the Note object inside when the user wants to save the modified note. However, I don't know how to access the backing NoteListItem from the qml delegate. the modelData seems to be something else. Is there any way to do so? If i could wrap the Note object in a QVariant I could access it easily through roles but when I tried it like this

QVariant NoteListItem::data(int role) {
    switch (role) {
    case Title:
        return note.getTitle();
    case NoteText:
        return note.getText();
    case NoteObject:
        return QVariant::fromValue(note);
    default:
        return QVariant();
    }
}

it resulted in a compiler error saying

qmetatype.h:642: error: invalid application of 'sizeof' to incomplete type 'QStaticAssertFailure'

Or should i try to access the selected list item from the backing code? Is there any way for that? Dou you have any ideas?

Thanks for your time. Regards, Peter

Here is my approach - http://stackoverflow.com/questions/14423372/how-to-access-items-stored-in-a-qabstractlistmodel-in-qmlby-delegates-otherwis/14424517#14424517 — Pavel Osipov, May 07 '13 at 10:03

score 10 · Accepted Answer · edited Nov 30 '16 at 06:19

10

This took me a very long time to find, as there are many incorrect solutions on Stackoverflow.

The pure QML way is to use a DelegateModel and access it from QML as follows:

import QtQuick 2.4
import QtQml.Models 2.1

ListView {
    property var currentSelectedItem

    onCurrentItemChanged{
            // Update the currently-selected item
            currentSelectedItem = myDelegateModel.items.get(currentIndex).model;
            // Log the Display Role
            console.log(currentSelectedItem.display);
    }

    model: DelegateModel {
        id: myDelegateModel
        model: myAbstractItemModel
        delegate: {
            // Define delegates here
        }
    }
}

This line returns an object (var) that you can access in the same way as within a delegate: myDelegateModel.items.get(currentIndex).model

This example assumes you are only using the default DelegateModelGroup.

See http://doc.qt.io/qt-5/qml-qtqml-models-delegatemodel.html and http://doc.qt.io/qt-5/qml-qtqml-models-delegatemodelgroup.html#get-method method

edited Nov 30 '16 at 06:19

Russ

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answered Jul 03 '15 at 12:33

Richard1403832

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Thank you so much! There are numerous more current answers that involve very tedious workarounds like manually implementing a `get` method in model implementation with custom notifiers and other mess. This is a clean built-in solution that just works – Curtwagner1984 Dec 15 '21 at 08:57
Does the delegate item get destroyed when it scrolled out of the viewport? – Logan Aug 30 '22 at 14:53
@Logan Delegate items will eventually either be destroyed or *re-used*. This is why it is very important not to maintain any state in a delegate, everything must come from the model. – Richard1403832 Sep 27 '22 at 10:56
@Richard1403832 Yes, that's why I am asking. Looking at it now the `currentSelectedItem` is bound to the model of the current item at the time of the item changing, so the state of the `currentSelectedItem` should always be valid even if the item which the model came from scrolls out of view and gets destroyed? – Logan Sep 27 '22 at 16:02
As far as I know the current item will always be either null (during construction/model reassignment) or valid. It won't point to a destroyed object. – Richard1403832 Oct 26 '22 at 15:34

How to access ListView's current item from qml

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