void Widget::mousePressEvent(QMouseEvent *event)
{
    origin = event->pos();
    if (!rubberBand)
        rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
    rubberBand->setGeometry(QRect(origin, QSize()));
    rubberBand->show();
}

void Widget::mouseMoveEvent(QMouseEvent *event)
{
    rubberBand->setGeometry(QRect(origin, event->pos()).normalized());
}

void Widget::mouseReleaseEvent(QMouseEvent *event)
{
    rubberBand->hide();
    // determine selection, for example using QRect::intersects()
    // and QRect::contains().
}

Member Function Documentation

QRubberBand::QRubberBand(QRubberBand::Shape s, QWidget *p = nullptr)

Constructs a rubber band of shape s, with parent p.

By default a rectangular rubber band (s is Rectangle) will use a mask, so that a small border of the rectangle is all that is visible. Some styles (e.g., native macOS) will change this and call QWidget::setWindowOpacity() to make a semi-transparent filled selection rectangle.

[virtual] QRubberBand::~QRubberBand()

Destructor.

[override virtual protected] void QRubberBand::changeEvent(QEvent *e)

Reimplemented from QWidget::changeEvent().

[override virtual protected] bool QRubberBand::event(QEvent *e)

Reimplemented from QWidget::event().

[protected] void QRubberBand::initStyleOption(QStyleOptionRubberBand *option) const

Initialize option with the values from this QRubberBand. This method is useful for subclasses when they need a QStyleOptionRubberBand, but don't want to fill in all the information themselves.

See also QStyleOption::initFrom().

void QRubberBand::move(int x, int y)

Moves the rubberband to point (x, y).

See also resize().

void QRubberBand::move(const QPoint &p)

This is an overloaded function.

Moves the rubberband to point p.

See also resize().

[override virtual protected] void QRubberBand::moveEvent(QMoveEvent *)

Reimplemented from QWidget::moveEvent().

[override virtual protected] void QRubberBand::paintEvent(QPaintEvent *)

Reimplemented from QWidget::paintEvent().

void QRubberBand::resize(int width, int height)

Resizes the rubberband so that its width is width, and its height is height.

See also move().

void QRubberBand::resize(const QSize &size)

This is an overloaded function.

Resizes the rubberband so that its new size is size.

See also move().

[override virtual protected] void QRubberBand::resizeEvent(QResizeEvent *)

Reimplemented from QWidget::resizeEvent().

void QRubberBand::setGeometry(const QRect &rect)

Sets the geometry of the rubber band to rect, specified in the coordinate system of its parent widget.

See also QWidget::geometry.

void QRubberBand::setGeometry(int x, int y, int width, int height)

This is an overloaded function.

Sets the geometry of the rubberband to the rectangle whose top-left corner lies at the point (x, y), and with dimensions specified by width and height. The geometry is specified in the parent widget's coordinate system.

QRubberBand::Shape QRubberBand::shape() const

Returns the shape of this rubber band. The shape can only be set upon construction.

[override virtual protected] void QRubberBand::showEvent(QShowEvent *e)

Reimplemented from QWidget::showEvent().