QIcon::fromTheme(xxx, someFallback)

[Olivier Goffart]

On Friday 21. August 2015 22:30:37 David Faure wrote:


> > I would also approve a change to Qt to add an overload of QIcon::fromTheme
> > with only one argument without a fallback. (this would be binary
> > compatible, and source compatible unless someone took the address of
> > QIcon::fromTheme)

> I thought about that, but that would change behavior of existing code, no?
> 
> Currently: QIcon::fromTheme("foo").isNull() is true if "foo" isn't found.
> If we add a one-arg overload: QIcon::fromTheme("foo").isNull() would be
> false, and QIcon::fromTheme("foo", QIcon()).isNull() would be true. The old
> behavior (for these rare apps that care) would require adding an explicit
> null-icon second arg. I wish this would have been done this way from the
> start, but we can't make that change now.

Ah ok, i first tought that the problem was the call to availableSizes.
But other problem is also the fact that we want to return a null icon if not 
found.

Fo this mean we could change QIcon::isNull fo be something like

if (!d) return true;
if (d->notNull) return false;
bool null;
d->virtualHook(CheckNull, &null);
if (null) {
	const_cast(this)->operator=(QIcon())
} else {
   d->notNull = true;
}
return null;


So than isNull is also lazy, and the problem is solved... is it not?

> Well, there is one solution: QIcon("foo"), the existing fileName ctor,
> if we add the fact that "if not found in the current dir then the icon
> will be looked up in the theme". That means one stat() per QIcon,
> but that's nothing compare to the current QIcon::fromTheme().

That could be a solution.
 
> And from the documentation, it looks like QIcon(QString) already
> behaves the optimal way, i.e. you don't get isNull() if the file doesn't
> exist, because "The file will be loaded on demand." right?
> That's exactly what I want for icons loaded from a theme, and
> which QIcon::fromTheme() doesn't allow implementing, due
> to its requirement to immediately find out if a null icon
> (or a specific fallback) should be returned instead.

And I think this behaviour is also confusing.

-- 
Olivier