How to add a hover transition to QPushButton?

Question

I try to make a custom QPushButton with a stylesheet. I want to custom color of button when we mouse over it. It works, but I want to put a transition duration.

Answer 1

Cause

QSS is not CSS. There is no transition property. Here is a list of all available properties.

Solution

Instead of using stylesheets, I would suggest you to take another path, which is longer, but gives you more flexibility. Here is the solution:

1. Create a subclass of QPushButton, e.g. AnimatedHoverButton

2. Get notified about QEvent::HoverEnter and QEvent::HoverLeave events by reimplementing QPushButton::event

   bool AnimatedHoverButton::event(QEvent *event)
   {
       switch (event->type()) {
       case QEvent::HoverEnter:
           animateHover(true);
           break;
       case QEvent::HoverLeave:
           animateHover(false);
           break;
       }
   
       return QPushButton::event(event);
   }
   

3. Create the in and out transition by using QVariantAnimation

   void AnimatedHoverButton::animateHover(bool in)
   {
       const QColor &baseColor(palette().brush(QPalette::Button).color());
       const QColor &highlightColor(palette().brush(QPalette::Highlight).color());
       QColor startValue(in ? baseColor : highlightColor);
   
       if (m_transition) {
           startValue = m_transition->currentValue().value<QColor>();
           m_transition->stop();
       }
   
       m_transition = new QVariantAnimation(this);
   
       m_transition->setStartValue(startValue);
       m_transition->setEndValue(in ? highlightColor : baseColor);
       m_transition->setDuration(m_duration);
   
       connect(m_transition, &QVariantAnimation::valueChanged, [this](const QVariant &value){
           m_currentColor = value.value<QColor>();
           repaint();
       });
   
       connect(m_transition, &QVariantAnimation::destroyed, [this](){
           m_transition = nullptr;
       });
   
       m_transition->start(QAbstractAnimation::DeleteWhenStopped);
   }
   

4. Paint the button by reimplementing the QPushButton::paintEvent event handler and taking into account the current value of the animation

   void AnimatedHoverButton::paintEvent(QPaintEvent * /*event*/)
   {
       QStylePainter painter(this);
       QStyleOptionButton option;
       QPalette p(palette());
   
       initStyleOption(&option);
   
       p.setBrush(QPalette::Button, m_currentColor);
   
       option.palette = p;
       option.state |= QStyle::State_MouseOver;
   
       painter.drawControl(QStyle::CE_PushButton, option);
   }
   

Note: This solution uses the widget's palette to set the start and end values of the animation.

Example

The solution might seem complicated, but fortunatelly I have prepared a working example for you of how to implement and use the AnimatedHoverButton class.

The following code fragment uses the AnimatedHoverButton class to produce a result, similar to the CSS example you have provided:

auto *button = new AnimatedHoverButton(tr("Hover Over Me"), this);

QPalette p(button->palette());

p.setBrush(QPalette::Button, QColor("#F89778"));
p.setBrush(QPalette::ButtonText, QColor("#FFFFFF"));
p.setBrush(QPalette::Highlight, QColor("#F4511E"));

button->setPalette(p);
button->setTransitionDuration(300);

setCentralWidget(button);
setContentsMargins(10, 10, 10, 10);

The full code of the example is available on GitHub.

Result

The given example produces the following result:

Answer 2

You can use Animation.

MyButton.h

#include <QPushButton>
#include <QColor>
#include <QPropertyAnimation>

class MyButton : public QPushButton
{
    Q_OBJECT
    Q_PROPERTY(QColor color READ GetColor WRITE SetColor)

public:
    explicit MyButton(QWidget *parent = 0);

    void SetColor(const QColor& color);
    const QColor& GetColor() const;

protected:
    bool eventFilter(QObject *obj, QEvent *e);

private:
    QColor m_currentColor;

    QPropertyAnimation m_colorAnimation;

    void StartHoverEnterAnimation();
    void StartHoverLeaveAnimation();
};

MyButton.cpp

#include "MyButton.h"

#include <QEvent>
#include <QDebug>

MyButton::MyButton(QWidget *parent) :
    QPushButton(parent),
    m_colorAnimation(this, "color")
{
    this->installEventFilter(this);
}

void MyButton::SetColor(const QColor& color)
{
    m_currentColor = color;
    QString css = "QPushButton { border-radius: 5px; ";
    css.append("border: 1.5px solid rgb(91,231,255); ");
    QString strColor = QString("rgb(%1, %2, %3)").arg(color.red()).arg(color.green()).arg(color.blue());
    css.append("background-color: " + strColor + "; }");
    setStyleSheet(css);
}

const QColor& MyButton::GetColor() const
{
    return m_currentColor;
}

bool MyButton::eventFilter(QObject *obj, QEvent *e)
{
    if (e->type() == QEvent::HoverEnter) {
        StartHoverEnterAnimation();
    }

    if (e->type() == QEvent::HoverLeave) {
        StartHoverLeaveAnimation();
    }

    return false;
}

void MyButton::StartHoverEnterAnimation()
{
    m_colorAnimation.stop();

    m_colorAnimation.setDuration(900); //set your transition
    m_colorAnimation.setStartValue(GetColor()); //starts from current color
    m_colorAnimation.setEndValue(QColor(100, 100, 100));//set your hover color

    m_colorAnimation.setEasingCurve(QEasingCurve::Linear);//animation style

    m_colorAnimation.start();
}

void MyButton::StartHoverLeaveAnimation()
{
    m_colorAnimation.stop();

    m_colorAnimation.setDuration(900); //set your transition
    m_colorAnimation.setStartValue(GetColor()); //starts from current color
    m_colorAnimation.setEndValue(QColor(255, 0, 0));//set your regular color

    m_colorAnimation.setEasingCurve(QEasingCurve::Linear);//animation style

    m_colorAnimation.start();
}

It will conflict with external qss setting. So set all qss in SetColor.