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Thread: QGraphicsItem: pure virtual method call problem

  1. #1
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    Default QGraphicsItem: pure virtual method call problem

    Hi every body,
    Please help me with this problem:
    I have a class TrackObject that derived from QgsmapcanvasItem to draw a dynamic object on Map, the QgsMapcanvasItem is derived from QGraphicsItem. sometimes i get a pure virtual method call exception and the program is crashed. the "pure virtual method call" exception occured when i create a new TrackObject or delete the TrackObject. I use QGis for MAP and QT version 4.7.4 on OpenSuse OS.

    the attachment is my exception.

    Thanks in advance!
    Attached Images Attached Images

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    Default Re: QGraphicsItem: pure virtual method call problem

    Pure virtual if directly or indirectly called from base class constructor or destructor causes such messages. While direct calling causes linking failure in gcc4.x, indirect calling is not detected and leads to crash.

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    Default Re: QGraphicsItem: pure virtual method call problem

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

    Edit: beaten to it.

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    Default Re: QGraphicsItem: pure virtual method call problem

    Quote Originally Posted by ChrisW67 View Post
    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:
    1. TrackObject::TrackObject(QgsMapCanvas* canvas) : QgsMapCanvasItem(canvas)
    2. {
    3. mSize = 16;
    4. trackInfo = NULL;
    5. heading = 0;
    6. speed = 0;
    7. fColor = QColor(0, 0, 0);
    8. mLastReceiveTime = time(NULL);
    9. bActive = false;
    10. bDrawHeading = true;
    11. nOnwFligh = 0;
    12. textPosition = 0;
    13. nBateryId = 0;
    14. targetStatus = FilterUnknown;
    15. nTrackID = -1;
    16. nTrackNumber = -1;
    17. isDisplaying = true;
    18. setFlag(ItemIsMovable);
    19. }
    To copy to clipboard, switch view to plain text mode 
    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:
    1. TrackObject::~TrackObject()
    2. {
    3. if(trackInfo)
    4. {
    5. delete trackInfo;
    6. trackInfo = NULL;
    7. }
    8. }
    To copy to clipboard, switch view to plain text mode 
    the application not crashed immediately when started but it only run within about 15 - 30 mins after some create and delete TrackObject times.
    Last edited by phuongot; 17th January 2012 at 08:30.

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    Default Re: QGraphicsItem: pure virtual method call problem

    What is QgsMapCanvasItem::QgsMapCanvasItem() and setFlag() doing?
    Last edited by ChrisW67; 17th January 2012 at 08:12.
    "We can't solve problems by using the same kind of thinking we used when we created them." -- Einstein
    If you are posting code then please use [code] [/code] tags around it - makes addressing the problem easier.

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    Default Re: QGraphicsItem: pure virtual method call problem

    Quote Originally Posted by ChrisW67 View Post
    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

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