How to animate the transparency of a child QPushButton using QPropertyAnimation ?

[daudiam]

I want to progressively decrease the opacity of a QPushButton over a time of 2 seconds to complete transparency. For that I used the QPropertyAnimation class and used the property "windowOpacity" of the button to achieve the effect. But that worked only for a standalone QPushButton. When I assigned a parent to the button, the effect disappeared. Is there any way of achieving the same effect for child buttons ?

[tbscope]

This is the side effect of child widgets not being windows in Qt.
You can only do the opacity on the parent.

edit: however, this doesn't mean it is impossible.
Use a style specific for your button.

[daudiam]

Thanks. But how do we specify transparency levels in buttons ? I mean, any functions, any property which I can set.

[tbscope]

Read about QPalette.

[wysota]

Let's try to go for a quick solution. Subclass QPushButton, add a qreal "opacity" property to the button subclass (so that you can animate its value) and reimplement the paint event. In the event implementation there are two things that might work. First you might try setting up a painter and calling QPainter::setOpacity() before calling the base class implementation or if this doesn't work, call the base class implementation first and then use QPainter::setCompositionMode() to setup a composition mode that will allow you to paint the alpha channel to what is already painted using an opacity of your choice. Which composition mode to choose is left as an exercise to the reader.