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Type: Bug
Resolution: Done
Priority: P2: Important
Fix Version/s: 5.12.2, 5.12.3, 5.13.1, 5.14.0 Alpha
Affects Version/s: 5.12
Component/s: QML: Declarative and Javascript Engine
Labels:
- earmarked_by_ulf

Platform/s:

Linux/X11
Commits:
dbc811e164019b5f9ce371cb7b49d695644f6a90 (qt/qtdeclarative/5.12)

Description

In the following example, a delegate model uses a QQmlListProperty as a source model. The DelegateModel is used by a ListView. In this case, a change in the QQmlListProperty leads to a Segmentation Fault during the call of the the following line:

// qqmldelegatemodel.cpp line 592
QQmlDelegateModelItem *cacheItem = QQmlDelegateModelItem::dataForObject(object);

The error does not occur when list view does not use the delegate model or if the DelegateModel does not use the underlying QQmlListProperty.

Also, by avoiding the DelegateModel all together and having the ListView accessing the QQmlListProperty model directly, also does not crash.

Down here there is the QML part of the example, in the attached ZIP file, you can find the whole project and additionally the backtrace caused by the Segmentation Fault.

The QQmlListProperty model of RandomObjectsProvider contains a very simple elements of a QObjects derivative with random content.

The changes in the model are caused by the objectsProvider.createNewElements() call. This method is triggered every 300ms

// QML is shaped as follows
import QtQuick.Window 2.2
import QtQuick 2.6
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3
import QtQml.Models 2.11
import example 1.0
Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    ListView {
        anchors.fill: parent
        model: delegateModel
    }
    DelegateModel {
        id: delegateModel
        model: objectsProvider.randomObjects
        delegate: delegate
        filterOnGroup: "visible"
        groups: [
            DelegateModelGroup {
                id: visibleGroup
                name: "visible"
                includeByDefault: false
            }
        ]        items.onChanged: {
            Qt.callLater(update)
            // very similar backtrace with `update();`
        }
        function update() {
            if(items.count>0)
                items.addGroups(0, items.count, ["visible"]);
        }
    }
    Component {
        id: delegate
        Rectangle {
            anchors.left: parent.left
            anchors.right: parent.right
            height: 30
            Text {
                text: "Data: " + (!modelData ? name : modelData.name)
            }
        }
    }
    Timer {
        id: changeModelTimer
        property int count: 0
        interval: 300
        onTriggered: {
            count++;
            console.log("Round", count);
            objectsProvider.createNewElements();
            console.log("Number of elements",
                objectsProvider.count());
            if(count>=100) {
                Qt.quit()
            }
        }
        repeat: true
    }
    Component.onCompleted: {
        objectsProvider.createNewElements();
        changeModelTimer.start();
    }
    RandomObjectsProvider {
        id: objectsProvider
    }
}