My app is crashing probably NOT! Due to Loader

[Marek]

Hi.

My app is crashing during startup on Android phone, never on Desktop. What is more it is crashing very randomly, on some phones is works every time (Android 6.0) on some never (6.0.1, 5.0.1), on my old Samsung S3 Android 4.2.2 sometimes I compile and it works, sometimes not.
I suspect this is due to Loader which I added to have a SplashSccreen, according to this bug Object destroyed during incubation it happens when Loader is in acynchronous mode.
However, even when asynchronous:false is set app is crashing randomly.
Debuger shows that is has stopped in main.cpp on line: "engine.load(QUrl(QLatin1String("qrc:/main.qml")));"
with output:

1  QVector<QPointer<QQuickItem>>::reallocData(int, int, QFlags<QArrayData::AllocationOption>)                 0x53e89b2c 
2  QVector<QPointer<QQuickItem>>::resize(int)                                                                 0x53e89c78 
3  QQuickRepeater::regenerate()                                                                               0x53e88b42 
4  QQuickRepeater::componentComplete()                                                                        0x53e8990e 
5  QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&)                                                   0x53a3f42e 
6  QQmlIncubatorPrivate::incubate(QQmlInstantiationInterrupt&)                                                0x53a08b48 
7  QQmlEnginePrivate::incubate(QQmlIncubator&, QQmlContextData *)                                             0x53a08db2 
8  QQmlComponent::create(QQmlIncubator&, QQmlContext *, QQmlContext *)                                        0x53a074ea 
9  QQuickLoaderPrivate::_q_sourceLoaded()                                                                     0x53e8a908 
10 QQuickLoaderPrivate::load()                                                                                0x53e8a96a 
11 QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&)                                                   0x53a3f42e 
12 QQmlComponentPrivate::complete(QQmlEnginePrivate *, QQmlComponentPrivate::ConstructionState *)             0x53a062ca 
13 QQmlComponentPrivate::completeCreate()                                                                     0x53a06322 
14 QQmlComponent::create(QQmlContext *)                                                                       0x53a0624e 
15 QQmlApplicationEnginePrivate::finishLoad(QQmlComponent *)                                                  0x53a3b57c 
16 QQmlApplicationEnginePrivate::startLoad(QUrl const&, QByteArray const&, bool)                              0x53a3b69c 
17 QQmlApplicationEngine::load(QUrl const&)                                                                   0x53a3b72a 
18 main                                                                                           main.cpp 60 0x546dc024 
19 startMainMethod(void *)                                                                                    0x543a2336 
20 __thread_entry                                                                                             0x4021c3ec 
21 pthread_create                                                                                             0x4021bad8 
22 ??                                                                                                                    

I have my main.qml like this

import QtQuick 2.9

Item {
    signal qmlLoaded()
    Loader {
        id: mainWindowLoader
        active: false
        source: "qrc:/window.qml"
        asynchronous: false
        onLoaded: {
            item.visible = true;
            splashScreenLoader.item.visible = false;
            splashScreenLoader.source = "";
            qmlLoaded()
        }
    }

    Loader {
        id: splashScreenLoader
        source: "qrc:/splashscreen.qml"
        onLoaded: {
            mainWindowLoader.active = true;
        }
    }
}

So my question is, do you suspect it can be due to Loader and this bug?
Is there some more debug I can get? I mean there is no specific error
I'm using delegates for my ListView, maybe this is a problem ?
I will try to get rid of the loader and SplashScreen and see if it helps.
I'm using Qt 5.9.1 on Linux 64Bit

Best Regards
Marek

[Marek]

Hi,

After getting rid of the Loader and half of my application I have found a problem - uninitialized variable in C++ model, this variable was a property and has been an input for PageIndicator (count: PictureModel.rows)

//C++ part
class PictureModel : public QAbstractListModel
{
    Q_OBJECT
public:
    enum ItemRoles {
        IdRole = Qt::UserRole + 1,
        PicNameRole = Qt::UserRole + 2,
        PicAvailable = Qt::UserRole + 3,
    };
    Q_PROPERTY(int rows MEMBER m_rows NOTIFY rowsChanged)
....

//qml part
ListView {
    id: plantPicView
    snapMode: ListView.SnapOneItem
    highlightRangeMode: ListView.StrictlyEnforceRange
    orientation: Qt.Horizontal
    width:(PictureModel.rows ? parent.width : 0)
    height:(PictureModel.rows ? 3*width/4 : 0)
    anchors.horizontalCenter: parent.horizontalCenter
    clip: true
    z:10

    model: PictureModel
    delegate: PictureDelegate {
        z:11
        source: pic_name_role
    }
    spacing: 0
}
PageIndicator {
    id:pageIndicator
    anchors.top: plantPicView.bottom
    height: titleText.height/2
    anchors.horizontalCenter: listViewRect.horizontalCenter
    currentIndex: plantPicView.currentIndex
    count: PictureModel.rows

    delegate: Rectangle {
        width: titleText.height/2
        height: titleText.height/2

        radius: width / 2
        color: "#21be2b"

        opacity: index === plantPicView.currentIndex ? 0.95 : pressed ? 0.7 : 0.45

        Behavior on opacity {
            OpacityAnimator {
                duration: 100
            }
        }
        MouseArea {
            anchors.fill: parent
            onClicked: {
                plantPicView.currentIndex = index
            }
        }
    }
}

But here comes really really important question:
Are there some techniques/tools that should show me this error, of which I don't know about, like QML profiling or something, maybe except: "Remember always initialize your variables" :)
All I could see running debugger in QtCreator was that something was resized/reallocated

1  QVector<QPointer<QQuickItem>>::reallocData(int, int, QFlags<QArrayData::AllocationOption>)                 0x53e89b2c 
2  QVector<QPointer<QQuickItem>>::resize(int)                                                                 0x53e89c78 
3  QQuickRepeater::regenerate()                                                                               0x53e88b42 
4  QQuickRepeater::componentComplete()                                                                        0x53e8990e 
5  QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&)                                                   0x53a3f42e                                                                
6  QQmlComponentPrivate::complete(QQmlEnginePrivate *, QQmlComponentPrivate::ConstructionState *)             0x53a062ca                                                                
7  QQmlComponentPrivate::completeCreate()                                                                     0x53a06322                                                                
8  QQmlComponent::create(QQmlContext *)                                                                       0x53a0624e                                                                
9  QQmlApplicationEnginePrivate::finishLoad(QQmlComponent *)                                                  0x53a3b57c                                                                
10 QQmlApplicationEnginePrivate::startLoad(QUrl const&, QByteArray const&, bool)                              0x53a3b69c                                                                
11 QQmlApplicationEngine::load(QUrl const&)                                                                   0x53a3b72a                                                                
12 main                                                                                           main.cpp 60 0x546dc024                                                                
13 startMainMethod(void *)                                                                                    0x543a2336                                                                
14 __thread_entry                                                                                             0x4021c3ec                                                                
15 pthread_create                                                                                             0x4021bad8

Best Regards
Marek