[Qt-interest] Using QGraphicsLayouts inside QGraphicsWidgets

[Schimkowitsch Robert]

Hi, 

trying to get a few things straight:

> > I have methods to add and remove items from the ButtonBar, and I
> > basically expose the LinearLayout's SizeHint as the ButtonBar's
SizeHint
> > (so any outside layout will know how much room all my buttons need).

> That should not be necessary. The QGW and QGL items should do that for
you 
> with no code on your part. Just setting the layout is enough to do
this.

[...]

> Any time one of your custom buttons changes it's size it should call 
> QGraphicsWidget::updateGeometry(). This will take care of propagating
the 
> change in size hints up the widget/layout hierarchy.

In the constructor initialisation list, I initialize my LinearLayout
member thus:
m_Layout(this)

Of course, the layout itself will recognize when one of it's layout
items changes.
The question for me was how that information gets to my ButtonBar, so an
outer layout seeing my ButtonBar as one of it's LayoutItems will
invalidate itself.

Are you implying that telling the layout my ButtonBar is its parent will
be enough for the invalidation to propagate?

> At present this can take several iterations of the event loop due to a
bug in 
> QGV (http://bugreports.qt.nokia.com/browse/QTBUG-17244). The fix for
this is 
> coming in Qt 4.8.0 (and 4.7.4 if we get that release). The fix is
opt-in 
> though and you'll need to call:
> 
> QGraphicsLayout::setInstantInvalidatePropagation(true);
> 
> to make it happen in a single pass.

Good to know!

Thanks!

Robert Schimkowitsch


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