Question on Qt animation framework

Christoph Feck christoph at
Sat Aug 28 02:40:31 BST 2010

On Saturday 28 August 2010 03:11:27 Hugo Pereira Da Costa wrote:
> Hi all,
> I have a technical question concerning animations.

Not exactly KDE related, but I will answer anyway :)

> All over the place in oxygen QPropertyAnimations trigger updates of widgets
> with a slot/signal call a la:
> connect(
>   animation, SIGNAL( valueChanged( const QVariant& ) ),
>   widget, SLOT( update( void ) ) );

This is not how QPropertyAnimation is supposed to work. When you animate a 
property, lets say "opacity", then QPropertyAnimation internally calls 
"setOpacity" on the widget during the animation. Inside the "setOpacity" 
function, you compare the old and the new opacity, and when it changed, you 
call update() in that function.

There is no need to connect anything when using the QPropertyAnimation.

> Now, I also added:
> connect(
> 	animation, SIGNAL( finished( void ) ),
> 	widget, SLOT( update( void ) ) );
> The question is: does anyone know whether the second call necessary or
> superfluous, or in otherr words, when an animation runs, is it certified
> that it will always call a valueChanged signal with its endValue() before
> finishing.

If Qt does not do this, file a bug. It should even emit a single 
valueChanged() with the endValue at an animation of duration 0.

> I guess I can test it, but in case anyone knows that on top of his/her
> mind, that would spare me some nasty QDebug
> Thanks in advance,
> Hugo

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