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Details

Type: Bug
Resolution: Unresolved
Priority: P1: Critical
Fix Version/s: None
Affects Version/s: 6.6.2
Component/s: Quick: Other
Labels:
None
Environment:
Ubuntu 22.04

Platform/s:

Linux/Wayland

Description

I'm trying to drag & drop into a ListView, to move its items around. I've added automatic scrolling when drag position is on top or bottom of the list.

Problem faced: after a few auto-scrolling iterations, the drag operation seems to enter an invalid state: I lose visual feedback, but internally it seems to still be active. I get a "exited" event on the DropArea, as if the mouse cursor had left the ListView (which it didn't), but the drag is still active. I cannot do anything until I release the drag and start a new one.

A proof that something's going wrong internally: later when I quit the app, I get a crash related to what looks like a drag operation that was stuck.

I've attached a video that shows the problem.

Here is a minimal code that reproduces it:

Rectangle {
    anchors.fill: parent
    color: "black"

    DropArea {
        id: dropArea
        anchors.fill: parent

        onPositionChanged: drag => {
            const itemHeight = 50;
            if (drag.y < itemHeight && !list.moving) {
                scrollbar.decrease()
            } else if (drag.y > list.height - itemHeight && !list.moving) {
                scrollbar.increase()
            }
        }

        onEntered: status.text = "DropArea.onEntered"
        onExited: status.text = "DropArea.onExited"
    }

    ColumnLayout {
        anchors.fill: parent

        ListView {
            id: list
            Layout.fillWidth: true
            Layout.fillHeight: true
            spacing: 1
            model: 200
            boundsBehavior: Flickable.StopAtBounds
            clip: true

            ScrollBar.vertical: ScrollBar {
                id: scrollbar
                stepSize: 1. / list.count
            }

            delegate: Rectangle {
                id: listItem
                width: list.width
                height: 50
                color: "white"

                Text {
                    anchors.centerIn: parent; text: index; color: "black"
                }

                Drag.dragType: Drag.Automatic
                Drag.supportedActions: Qt.MoveAction

                DragHandler {
                    id: dragHandler
                    target: null

                    onActiveChanged: {
                        if (active) {
                            listItem.grabToImage(function (result) {
                                if (active) {
                                    listItem.Drag.imageSource = result.url;
                                    listItem.Drag.active = true;
                                }
                            });
                        } else {
                            listItem.Drag.active = false;
                        }
                    }
                }
            }
        }

        Text {
            id: status
            Layout.fillWidth: true
            Layout.fillHeight: false
            color: "white"
        }
    }
}

And the stack trace of the crash that occurs on exit (differs sometimes, but always related to drag):

 1# 0x0000702AA1C42520 in /lib/x86_64-linux-gnu/libc.so.6
 2# QQmlData::isSignalConnected(QAbstractDeclarativeData*, QObject const*, int) at /home/qt/work/qt/qtdeclarative/src/qml/qml/qqmlengine.cpp:373
 3# void doActivate<false>(QObject*, int, void**) at /home/qt/work/qt/qtbase/src/corelib/kernel/qobject.cpp:3928
 4# QQuickDragAttached::dragFinished(Qt::DropAction) at /home/qt/work/build/qtdeclarative/src/quick/Quick_autogen/include/moc_qquickdrag_p.cpp:1185
 5# QQuickDragAttachedPrivate::startDrag(QFlags<Qt::DropAction>) at /home/qt/work/qt/qtdeclarative/src/quick/items/qquickdrag.cpp:790
 6# QQuickDragAttached::qt_metacall(QMetaObject::Call, int, void**) at /home/qt/work/build/qtdeclarative/src/quick/Quick_autogen/include/moc_qquickdrag_p.cpp:1169
 7# QQmlPropertyData::writeProperty(QObject*, void*, QFlags<QQmlPropertyData::WriteFlag>) const at /home/qt/work/qt/qtdeclarative/src/qml/qml/qqmlpropertydata_p.h:340
 8# QQmlPropertyPrivate::write(QObject*, QQmlPropertyData const&, QVariant const&, QQmlRefPointer<QQmlContextData> const&, QFlags<QQmlPropertyData::WriteFlag>) at /home/qt/work/qt/qtdeclarative/src/qml/qml/qqmlproperty.cpp:1555
 9# QV4::QObjectWrapper::setProperty(QV4::ExecutionEngine*, QObject*, QQmlPropertyData const*, QV4::Value const&) at /home/qt/work/qt/qtdeclarative/src/qml/jsruntime/qv4qobjectwrapper.cpp:650
10# QV4::QObjectWrapper::setQmlProperty(QV4::ExecutionEngine*, QQmlRefPointer<QQmlContextData> const&, QObject*, QV4::String*, QFlags<QV4::QObjectWrapper::Flag>, QV4::Value const&) at /home/qt/work/qt/qtdeclarative/src/qml/jsruntime/qv4qobjectwrapper.cpp:466
11# QV4::QQmlTypeWrapper::virtualPut(QV4::Managed*, QV4::PropertyKey, QV4::Value const&, QV4::Value*) at /home/qt/work/qt/qtdeclarative/src/qml/qml/qqmltypewrapper.cpp:334
12# QV4::Object::virtualResolveLookupSetter(QV4::Object*, QV4::ExecutionEngine*, QV4::Lookup*, QV4::Value const&) at /home/qt/work/qt/qtdeclarative/src/qml/jsruntime/qv4object.cpp:813
13# QV4::Moth::VME::interpret(QV4::JSTypesStackFrame*, QV4::ExecutionEngine*, char const*) at /home/qt/work/qt/qtdeclarative/src/qml/jsruntime/qv4vme_moth.cpp:801
14# QV4::Moth::VME::exec(QV4::JSTypesStackFrame*, QV4::ExecutionEngine*) at /home/qt/work/qt/qtdeclarative/src/qml/jsruntime/qv4vme_moth.cpp:584
15# qfoDoCall(QV4::FunctionObject const*, QV4::Value const*, QV4::Value const*, int) at /home/qt/work/qt/qtdeclarative/src/qml/jsruntime/qv4functionobject.cpp:528
16# QJSValue::call(QList<QJSValue> const&) const at /home/qt/work/qt/qtdeclarative/src/qml/jsapi/qjsvalue.cpp:707
17# QQuickItemGrabResult::event(QEvent*) at /home/qt/work/qt/qtdeclarative/src/quick/items/qquickitemgrabresult.cpp:217
18# QApplicationPrivate::notify_helper(QObject*, QEvent*) at /home/qt/work/qt/qtbase/src/widgets/kernel/qapplication.cpp:3298
19# QCoreApplication::notifyInternal2(QObject*, QEvent*) at /home/qt/work/qt/qtbase/src/corelib/kernel/qcoreapplication.cpp:1121
20# QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) at /home/qt/work/qt/qtbase/src/corelib/kernel/qcoreapplication.cpp:1906
21# postEventSourceDispatch(_GSource*, int (*)(void*), void*) at /home/qt/work/qt/qtbase/src/corelib/kernel/qeventdispatcher_glib.cpp:244
22# g_main_context_dispatch in /lib/x86_64-linux-gnu/libglib-2.0.so.0
23# 0x0000702AA1708258 in /lib/x86_64-linux-gnu/libglib-2.0.so.0
24# g_main_context_iteration in /lib/x86_64-linux-gnu/libglib-2.0.so.0
25# QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) at /home/qt/work/qt/qtbase/src/corelib/kernel/qeventdispatcher_glib.cpp:394
26# QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) at /home/qt/work/qt/qtbase/src/corelib/kernel/qeventloop.cpp:181
27# QCoreApplication::exec() at /home/qt/work/qt/qtbase/src/corelib/kernel/qcoreapplication.cpp:1442

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drag-bug-capture.webm
107 kB
24 Apr '24 07:03

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For Gerrit Dashboard: QTBUG-124663
#	Subject	Branch	Project	Status	CR	V
575665,3	Fix destroying item in QQuickListView which is being dragged out	dev	qt/qtdeclarative	Status: NEW	0	0
600304,1	WIP debug window exit during DnD	dev	qt/qtbase	Status: NEW	-2	0

Auto-scrolling a ListView breaks drag operation

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