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Thread: Updating the boundingRect of a QGraphicsItem

  1. #1
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    Question Updating the boundingRect of a QGraphicsItem

    hi,

    i have a QGraphicsItemGroup with several items in it. The boundingRect is computed correctly according to the current boundingRects of the group members. Now i change the size of one member in the group, so that his boundingRect exceeds the group's boundingRect.
    But when I call group.boundingRect(), it was not updated. Is there any way to manually update the boundingRect of an existing item group? Even implementing an inherited version of boundingRect() in a child class of QGraphicsItemGroup does not work, because boundingRect in QGraphicsItemGroup is not virtual thus the graphics engine would only call the ancestors version, when treating the object as a QGraphicsItem.
    The only workaround i found is to remove an item from the group and adding it again, because then the boundingRect stored in the private variable d->itemsBoundingRect is updated. But that can't be the solution.

    I'd be grateful for any ideas.

  2. #2
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    Default Re: Updating the boundingRect of a QGraphicsItem

    Sure it's virtual...
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  3. #3
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    Default Re: Updating the boundingRect of a QGraphicsItem

    No, boundingRect() is only virtual in QGraphicsItem not in QGraphicsItemGroup. Here is the code from the implementation:
    Qt Code:
    1. /*!
    2.   \reimp
    3.  
    4.   Returns the bounding rect of this group item, and all its children.
    5. */
    6. QRectF QGraphicsItemGroup::boundingRect() const
    7. {
    8. Q_D(const QGraphicsItemGroup);
    9. return d->itemsBoundingRect;
    10. }
    To copy to clipboard, switch view to plain text mode 

    and the declaration in class QGraphicsItemGroup:
    Qt Code:
    1. 1062 QRectF boundingRect() const;
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    Last edited by robin2000; 14th August 2009 at 09:37.

  4. #4
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    Default Re: Updating the boundingRect of a QGraphicsItem

    Qt Code:
    1. #include <iostream>
    2. class A {
    3. public:
    4. virtual void function() { std::cout << "A" << std::endl; }
    5. };
    6.  
    7. class B : public A {
    8. public:
    9. void function() { std::cout << "B" << std::endl; }
    10. };
    11.  
    12. class C : public B {
    13. void function() { std::cout << "C" << std::endl; }
    14. };
    15.  
    16. int main(){
    17. A *obj = new A;
    18. obj->function();
    19. delete obj;
    20. obj = new B;
    21. obj->function();
    22. delete obj;
    23. obj = new C;
    24. obj->function();
    25. delete obj;
    26. return 0;
    27. }
    To copy to clipboard, switch view to plain text mode 
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  5. #5
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    Thumbs up Re: Updating the boundingRect of a QGraphicsItem

    Your so right. It didn't work in my case, because I tried to call QGraphicsItemGroup.boundingRect() instead of QGraphicsItem.boundingRect(). But that's easy to solve now.

    Thank you very much for your fast help. Learned something about inheritance

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