c++ - Toggle Switch in Qt

Question

I am trying to use an element which is the equivalent of Android Switches in Qt. I have found a ToggleSwitch in QML, but nothing in the actual C++ Qt libs. Am I just missing something or will I have to reimplement this widget myself?

Answer 1

Here is an example:

switch.h:

#pragma once
#include <QtWidgets>

class Switch : public QAbstractButton {
    Q_OBJECT
    Q_PROPERTY(int offset READ offset WRITE setOffset)
    Q_PROPERTY(QBrush brush READ brush WRITE setBrush)

public:
    Switch(QWidget* parent = nullptr);
    Switch(const QBrush& brush, QWidget* parent = nullptr);

    QSize sizeHint() const override;

    QBrush brush() const {
        return _brush;
    }
    void setBrush(const QBrush &brsh) {
        _brush = brsh;
    }

    int offset() const {
        return _x;
    }
    void setOffset(int o) {
        _x = o;
        update();
    }

protected:
    void paintEvent(QPaintEvent*) override;
    void mouseReleaseEvent(QMouseEvent*) override;
    void enterEvent(QEvent*) override;

private:
    bool _switch;
    qreal _opacity;
    int _x, _y, _height, _margin;
    QBrush _thumb, _track, _brush;
    QPropertyAnimation *_anim = nullptr;
};

switch.cpp:

Switch::Switch(QWidget *parent) : QAbstractButton(parent),
_height(16),
_opacity(0.000),
_switch(false),
_margin(3),
_thumb("#d5d5d5"),
_anim(new QPropertyAnimation(this, "offset", this))
{
    setOffset(_height / 2);
    _y = _height / 2;
    setBrush(QColor("#009688"));
}

Switch::Switch(const QBrush &brush, QWidget *parent) : QAbstractButton(parent),
_height(16),
_switch(false),
_opacity(0.000),
_margin(3),
_thumb("#d5d5d5"),
_anim(new QPropertyAnimation(this, "offset", this))
{
    setOffset(_height / 2);
    _y = _height / 2;
    setBrush(brush);
}

void Switch::paintEvent(QPaintEvent *e) {
    QPainter p(this);
    p.setPen(Qt::NoPen);
    if (isEnabled()) {
        p.setBrush(_switch ? brush() : Qt::black);
        p.setOpacity(_switch ? 0.5 : 0.38);
        p.setRenderHint(QPainter::Antialiasing, true);
        p.drawRoundedRect(QRect(_margin, _margin, width() - 2 * _margin, height() - 2 * _margin), 8.0, 8.0);
        p.setBrush(_thumb);
        p.setOpacity(1.0);
        p.drawEllipse(QRectF(offset() - (_height / 2), _y - (_height / 2), height(), height()));
    } else {
        p.setBrush(Qt::black);
        p.setOpacity(0.12);
        p.drawRoundedRect(QRect(_margin, _margin, width() - 2 * _margin, height() - 2 * _margin), 8.0, 8.0);
        p.setOpacity(1.0);
        p.setBrush(QColor("#BDBDBD"));
        p.drawEllipse(QRectF(offset() - (_height / 2), _y - (_height / 2), height(), height()));
    }
}

void Switch::mouseReleaseEvent(QMouseEvent *e) {
    if (e->button() & Qt::LeftButton) {
        _switch = _switch ? false : true;
        _thumb = _switch ? _brush : QBrush("#d5d5d5");
        if (_switch) {
            _anim->setStartValue(_height / 2);
            _anim->setEndValue(width() - _height);
            _anim->setDuration(120);
            _anim->start();
        } else {
            _anim->setStartValue(offset());
            _anim->setEndValue(_height / 2);
            _anim->setDuration(120);
            _anim->start();
        }
    }
    QAbstractButton::mouseReleaseEvent(e);
}

void Switch::enterEvent(QEvent *e) {
    setCursor(Qt::PointingHandCursor);
    QAbstractButton::enterEvent(e);
}

QSize Switch::sizeHint() const {
    return QSize(2 * (_height + _margin), _height + 2 * _margin);
}

main.cpp:

#include "switch.h"

    int main(int argc, char *argv[]) {
        QApplication a(argc, argv);
        QWidget *widget = new QWidget;
        widget->setWindowFlags(Qt::FramelessWindowHint);
        QHBoxLayout layout;
        widget->setLayout(&layout);
        Switch *_switch = new Switch;
        Switch *_switch2 = new Switch;
        _switch2->setDisabled(true);
        layout.addWidget(_switch);
        layout.addWidget(_switch2);
        widget->show();
        return a.exec();
    }

Update Aug 20'18

New Material Switch Widget!

style.h

/*
 * This is nearly complete Material design Switch widget implementation in qtwidgets module.
 * More info: https://material.io/design/components/selection-controls.html#switches
 * Copyright (C) 2018 Iman Ahmadvand
 *
 * This is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * It is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
*/

#ifndef STYLE_H
#define STYLE_H

#include <QtCore/qeasingcurve.h>

#define cyan500 QColor("#00bcd4")
#define gray50 QColor("#fafafa")
#define black QColor("#000000")
#define gray400 QColor("#bdbdbd")

Q_DECL_IMPORT void qt_blurImage(QPainter *p, QImage &blurImage, qreal radius, bool quality, bool alphaOnly, int transposed = 0); // src/widgets/effects/qpixmapfilter.cpp

namespace Style {

    using Type = QEasingCurve::Type;

    struct Animation {
        Animation() = default;
        Animation(Type _easing, int _duration) :easing{ _easing }, duration{ _duration } {

        }

        Type easing;
        int duration;
    };

    struct Switch {
        Switch() :
            height{ 36 },
            font{ QFont("Roboto medium", 13) },
            indicatorMargin{ QMargins(8, 8, 8, 8) },
            thumbOnBrush{ cyan500 },
            thumbOnOpacity{ 1 },
            trackOnBrush{ cyan500 },
            trackOnOpacity{ 0.5 },
            thumbOffBrush{ gray50 },
            thumbOffOpacity{ 1 },
            trackOffBrush{ black },
            trackOffOpacity{ 0.38 },
            thumbDisabled{ gray400 },
            thumbDisabledOpacity{ 1 },
            trackDisabled{ black },
            trackDisabledOpacity{ 0.12 },
            textColor{ black },
            disabledTextOpacity{ 0.26 },
            thumbBrushAnimation{ Animation(Type::Linear, 150) },
            trackBrushAnimation{ Animation(Type::Linear, 150) },
            thumbPosAniamtion{ Animation(Type::InOutQuad, 150) } {

        }

        int height;
        QFont font;
        QMargins indicatorMargin;
        QColor thumbOnBrush;
        double thumbOnOpacity;
        QColor trackOnBrush;
        double trackOnOpacity;
        QColor thumbOffBrush;
        double thumbOffOpacity;
        QColor trackOffBrush;
        double trackOffOpacity;
        QColor thumbDisabled;
        double thumbDisabledOpacity;
        QColor trackDisabled;
        double trackDisabledOpacity;
        QColor textColor;
        double disabledTextOpacity;
        Animation thumbBrushAnimation;
        Animation trackBrushAnimation;
        Animation thumbPosAniamtion;
    };

    inline QPixmap drawShadowEllipse(qreal radius, qreal elevation, const QColor& color) {
        auto px = QPixmap(radius * 2, radius * 2);
        px.fill(Qt::transparent);

        { // draw ellipes
            QPainter p(&px);
            p.setBrush(color);
            p.setPen(Qt::NoPen);
            p.setRenderHint(QPainter::Antialiasing, true);
            p.drawEllipse(QRectF(0, 0, px.size().width(), px.size().height()).center(), radius - elevation, radius - elevation);
        }

        QImage tmp(px.size(), QImage::Format_ARGB32_Premultiplied);
        tmp.setDevicePixelRatio(px.devicePixelRatioF());
        tmp.fill(0);
        QPainter tmpPainter(&tmp);
        tmpPainter.setCompositionMode(QPainter::CompositionMode_Source);
        tmpPainter.drawPixmap(QPointF(), px);
        tmpPainter.end();

        // blur the alpha channel
        QImage blurred(tmp.size(), QImage::Format_ARGB32_Premultiplied);
        blurred.setDevicePixelRatio(px.devicePixelRatioF());
        blurred.fill(0);
        {
            QPainter blurPainter(&blurred);
            qt_blurImage(&blurPainter, tmp, elevation * 4., true, false);
        }

        tmp = blurred;

        return QPixmap::fromImage(tmp);
    }

} // namespace Style

#endif // STYLE_H

switch.h

/*
 * This is nearly complete Material design Switch widget implementation in qtwidgets module.
 * More info: https://material.io/design/components/selection-controls.html#switches
 * Copyright (C) 2018-2020 Iman Ahmadvand
 *
 * This is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * It is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
*/

#ifndef SWITCH_H
#define SWITCH_H

#include <QtWidgets>
#include "style.h"

class Animator final : public QVariantAnimation {
    Q_OBJECT
    Q_PROPERTY(QObject* targetObject READ targetObject WRITE setTargetObject)

  public:
    Animator(QObject* target, QObject* parent = nullptr);
    ~Animator() override;

    QObject* targetObject() const;
    void setTargetObject(QObject* target);

    inline bool isRunning() const {
        return state() == Running;
    }

  public slots:
    void setup(int duration, QEasingCurve easing = QEasingCurve::Linear);
    void interpolate(const QVariant& start, const QVariant& end);
    void setCurrentValue(const QVariant&);

  protected:
    void updateCurrentValue(const QVariant& value) override final;
    void updateState(QAbstractAnimation::State newState, QAbstractAnimation::State oldState) override final;

  private:
    QPointer<QObject> target;
};

class SelectionControl : public QAbstractButton {
    Q_OBJECT

  public:
    explicit SelectionControl(QWidget* parent = nullptr);
    ~SelectionControl() override;

    Qt::CheckState checkState() const;

  Q_SIGNALS:
    void stateChanged(int);

  protected:
    void enterEvent(QEvent*) override;
    void checkStateSet() override;
    void nextCheckState() override;
    virtual void toggle(Qt::CheckState state) = 0;
};

class Switch final : public SelectionControl {
    Q_OBJECT

    static constexpr auto CORNER_RADIUS = 8.0;
    static constexpr auto THUMB_RADIUS = 14.5;
    static constexpr auto SHADOW_ELEVATION = 2.0;

  public:
    explicit Switch(QWidget* parent = nullptr);
    Switch(const QString& text, QWidget* parent = nullptr);
    Switch(const QString& text, const QBrush&, QWidget* parent = nullptr);
    ~Switch() override;

    QSize sizeHint() const override final;

  protected:
    void paintEvent(QPaintEvent*) override final;
    void resizeEvent(QResizeEvent*) override final;
    void toggle(Qt::CheckState) override final;

    void init();
    QRect indicatorRect();
    QRect textRect();

    static inline QColor colorFromOpacity(const QColor& c, qreal opacity) {
        return QColor(c.red(), c.green(), c.blue(), qRound(opacity * 255.0));
    }
    static inline bool ltr(QWidget* w) {
        if (nullptr != w)
            return w->layoutDirection() == Qt::LeftToRight;