QGraphicsItem: pure virtual method call problem

**ChrisW67** · 17th January 2012, 04:33

Are you calling virtual methods in the constructors or destructor of the TrackObject class?

Edit: beaten to it.

**phuongot** · 17th January 2012, 05:33

Originally Posted by ChrisW67

Are you calling virtual methods in the constructors or destructor of the TrackObject class?

Edit: beaten to it.

I sure that i did not call any virtual methods in my constructors or destructors.

here is my constructor, i only initialized some properties:

Qt Code:

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TrackObject::TrackObject(QgsMapCanvas* canvas) : QgsMapCanvasItem(canvas)
{
    mSize = 16;
    trackInfo = NULL;
    heading = 0;
    speed = 0;
    fColor = QColor(0, 0, 0);
    mLastReceiveTime = time(NULL);
    bActive = false;
    bDrawHeading = true;
    nOnwFligh = 0;
    textPosition = 0;
    nBateryId = 0;
    targetStatus = FilterUnknown;
    nTrackID = -1;
    nTrackNumber = -1;
    isDisplaying = true;
    setFlag(ItemIsMovable);
}

TrackObject::TrackObject(QgsMapCanvas* canvas) : QgsMapCanvasItem(canvas)
{
    mSize = 16;
    trackInfo = NULL;
    heading = 0;
    speed = 0;
    fColor = QColor(0, 0, 0);
    mLastReceiveTime = time(NULL);
    bActive = false;
    bDrawHeading = true;
    nOnwFligh = 0;
    textPosition = 0;
    nBateryId = 0;
    targetStatus = FilterUnknown;
    nTrackID = -1;
    nTrackNumber = -1;
    isDisplaying = true;
    setFlag(ItemIsMovable);
}

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and the destructor, just delete the trackinfo object. the TrackInfo object store some information about the coordinate (lontitude, latitude,..) and also not call any virtual function in its destructor:

Qt Code:

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TrackObject::~TrackObject()
{
    if(trackInfo)
    {
        delete trackInfo;
        trackInfo = NULL;
    }
}

TrackObject::~TrackObject()
{
    if(trackInfo)
    {
        delete trackInfo;
        trackInfo = NULL;
    }
}

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the application not crashed immediately when started but it only run within about 15 - 30 mins after some create and delete TrackObject times.

**ChrisW67** · 17th January 2012, 07:03

What is QgsMapCanvasItem::QgsMapCanvasItem() and setFlag() doing?

**phuongot** · 17th January 2012, 07:35

Originally Posted by ChrisW67

What is QgsMapCanvasItem::QgsMapCanvasItem() and setFlag() doing?

Hi ChrisW67,

The QgsMapCanvasItem is a class of QGis library. you can see the constructor of QgsMapcanvasItem here:http://qgis.org/api/qgsmapcanvasitem_8cpp-source.html. The setFlag is a member function of QGraphicsItem class: http://developer.qt.nokia.com/doc/qt...m.html#setFlag