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Details

Type: Bug
Resolution: Done
Priority: P1: Critical
Fix Version/s: 5.9.4, 5.10.1, 5.12.0
Affects Version/s: 5.7.1, 5.8.0 RC, 5.9.0, 5.13.0
Component/s: QML: Declarative and Javascript Engine, Quick: Controls 2
Labels:

Commits:
numerous

Description

Using customized controls in item views or asynchronous loader often leads to "Object destroyed during incubation" or "Error creating delegate". The problem occurs with basically any control when replacing the default background, content item, or any other building block with a custom one. Controls cleanup the old default content, which leads to a "Object destroyed during incubation" -error, and then the incubation of the whole control fails.

In item views the problem occurs occasionally, leading to missing delegate instances (QML VisualDataModel: Error creating delegate):

import QtQuick 2.6
import QtQuick.Controls 2.0

ApplicationWindow {
    visible: true
    width: 640
    height: 480

    GridView {
        id: gridThing;
        anchors.fill: parent;
        cellWidth: 75;
        cellHeight: 75;
        model: 500;

        delegate: Button {
            id: control
            text: "Test"
            width: gridThing.cellWidth;
            height: gridThing.cellHeight;
            background: Rectangle {
                implicitHeight: 20;
                implicitWidth: 20;
                color: "red";
                width: control.width;
                height: control.height;
                x: 0;
                y: 0;
            }
        }
    }
}

In asynchronous loaders the issue is 100% reproducible with certain control structures:

import QtQuick 2.6
import QtQuick.Controls 2.0

ApplicationWindow {
    id: root
    visible : true
    width   : 640
    height  : 480

    property bool  triggerTheBug: true // Swap this to see a normal display of the ComboBox

    StackView {
        id: myStackView
        anchors.fill: parent
        initialItem: Loader {
            anchors.fill: parent
            asynchronous    : triggerTheBug
            sourceComponent :
                ComboBox { popup      : Popup{} }         // BUG
            //ComboBox { background : Rectangle{} }     // BUG
            //ComboBox { contentItem: Rectangle{} }     // BUG
            //ComboBox { delegate   : ItemDelegate{} }  // NO BUG
        }
    }
}

Under the hood, the problem is that QQmlIncubator + QQmlObjectCreator + QQmlVMEGuard tracks all instantiated child objects using QPointer and doesn't like that any of them gets destroyed during the incubation process. Calling deleteLater() is not sufficient, because it would not be synchronized with the incubation controller.

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ObjectDestroyedDuringIncubation.zip
3 kB
03 Jul '19 15:17
test-case-qt-5.9.4.tar
25 kB
24 Jan '18 08:24

Issue Links

depends on

QTBUG-63200 Deferred properties are not always executed

Closed

is duplicated by

QTBUG-53400 Adding asynchronous Loader into StackView results in "Object destroyed during incubation" error

Closed

QTBUG-52096 Qt Quick Controls 2 Button fails creation in GridView

Closed

QTBUG-52955 Regression: ItemDelegate with overriden contentItem in ListView fails to create on Android

Closed

QTBUG-53496 Customized Qt.labs ComboBox won't display in an asynchronous Loader

Closed

is required for

AUTOSUITE-189 Regression on Qt 5.9.4 breaks Neptune Styling

Closed

QTBUG-85097 Async loader and QQC2: Object destroyed during incubation

Closed

relates to

QTBUG-98439 "Binding on contentItem is not deferred as requested by the DeferredPropertyNames class info because it constitutes a group property" when instantiating ScrollBar