How to make Qt widgets fade in or fade out?

Question

I am trying to fade in and fade out a QLabel or for that matter any QWidget subclass. I have tried with QGraphicsEffect, but unfortuna

Answer 1

Try expose some part of palette as property of label then animate it:

Q_PROPERTY(QColor color READ color WRITE setColor)

void MyLabel::setColor(const QColor &value) {
    QPalette palette;
    palette.setBrush(QPalette::WindowText, value);
    setPalette(palette);
}

QColor MyLabel::color() {
    return palette(QPalette::Normal, QPalette::Window).
}

void MyLabel::startFadeOutAnimation() {
    QPropertyAnimation *animation = new QPropertyAnimation(label, "color", this);
    QColor c = label->color();
    animation->setKeyValueAt(0, c);
    c.setAlpha(0);
    animation->setKeyValueAt(1, c);
    animation->setEasingCurve(QEasingCurve::OutQuad);
    animation->setDuration(1000);
    animation->start(QAbstractAnimation::DeleteWhenStopped);
}

You can try avoid subclassing by defining and registering new interpolator which will handle QPalette qRegisterAnimationInterpolator, but this is a bit complicated.