QGraphicsItem geometry change implementation

[Narada]

I am trying to figure out how objects in a QGraphics Scene/View can be manipulated and redrawn.

From what I have learnt so far, when a QGraphicsItem needs to be added to the scene,

1. The object is derived from QGraphicsItem.
2. boundingRect(), and paint() needs to be reimplemented.
3. If some of the sizes need to be changed, use prepareGeometry(), and update().

So, I am working with two actions. One to add a box to the scene, and the other to increase the size when selected.

I tried to get it to work in one application and it did not work.(diagram.zip). The sizes of the item seem to reset before painting. I can see this if I keep increasing the size and trap the code. However, under certain paths it seem to work. For example, if I add a child to a box and select the parent, the size of the parent can be changed programmatically.

However, I created the minimum code required and it worked.
The code is in GrScene.zip

Why is there a difference in behavior?

Thanks in advance.

[d_stranz]

In this code:

void DiagramWindow::increaseSize()
{
 
    QList<QGraphicsItem *> items = scene->selectedItems();
    if (items.count() == 1) {
        Node *selNode = dynamic_cast<Node *>(items.first());
		selNode->increaseSize();
    }
	return;
}

void DiagramWindow::increaseSize()
{

    QList<QGraphicsItem *> items = scene->selectedItems();
    if (items.count() == 1) {
        Node *selNode = dynamic_cast<Node *>(items.first());
		selNode->increaseSize();
    }
	return;
}

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What happens if the selected node is a child of another node? I think in that case, both nodes will be marked as selected so your count will be 2, not 1. Have you looked at the size of the count in the cases where "works" and "doesn't work"?

[Narada]

The count does not seem to matter. However, the path it gets there to increase the size seems to.

MainWindow::increaseSize() --> Node::increaseSize() - does not work. Actually it resets the size. No idea how that happens
MainWindow::selectedNode() --> Node::increaseSize() - seems to work.


If I go through the second path and try the first path, the sizes get reset.

If I try to trace the code, it goes into the moc_ code. I am wondering if some of the variables are initialized here. I cannot trace the code all the way.

[d_stranz]

The count does not seem to matter.

Of course the count matters. Your code (in either example) will do nothing if the selected node count is not exactly 1.

In your DiagramWindow:: selectedNode() code, you -are- resetting the node size to nodeh x nodew when the node has no children. And in addChild(), since you call this method -before- you add a child to it, you are resetting the size there as well.

I'm not sure why you wrote selectedNode() that way, but it looks like some confused thinking about what should happen when you add a child node.