Question

I am writing an image viewer with Qt based on the QGraphicsScene feature of Qt. I am creating model of each image in a class called ImageModel and manage the display of the image in a class called ImageView. The ImageView class is as follows (just the part that is interesting):

class ImageView
{
public:
    ImageView(QWidget *parent);

    QGraphicsView * getView() {return view; }

private:

    //qgraphics scene elements
    QGraphicsScene *scene;
    QGraphicsView *view;
    QGraphicsPixmapItem *curItem;


};

The constructor for the class is as follows:

ImageView::ImageView(QWidget *parent)
{

    //create scene and view with parent the main window
    //such that the memory management is done by qt
    scene = new QGraphicsScene(parent);
    view = new QGraphicsView(parent);

    view->setScene(scene);
}

Also I have pointer to an ImageView in my derivation of the QMainWindow.

My question is: should I let Qt do the memory management by seting my main window as parent of the view and the scene or should I take care of the memory management myself (leave the view and the scene without parents and delete them in the class destructors)? What is a good strategy in this case?

Answer 1

If you want the view to be nested inside the main window, then you will have to make it a child.

For your general question, this really comes down to your desired object lifetimes and ownership semantics. If you don’t want to the view/scene to outlive the main window then yes they should be children. You still have the option to delete them through other means at an earlier time.