#ifndef RUBBERBANDSTYLE_H
#define RUBBERBANDSTYLE_H

#include <QBrush>
#include <QPainter>
#include <QPen>
#include <QProxyStyle>
#include <QRect>
#include <QStyleOptionRubberBand>

class RubberbandStyle : public QProxyStyle
{
    typedef QProxyStyle base_type;

public:
    RubberbandStyle(const QPen& pen, const QBrush& brush, QStyle* style = nullptr)
        : QProxyStyle(style)
        , pen_(pen)
        , brush_(brush)
    {
    }

    ~RubberbandStyle() override
    {
    }

    void drawControl(ControlElement element, const QStyleOption* option, QPainter* painter, const QWidget* widget = nullptr) const override
    {
        if (CE_RubberBand == element)
        {
            painter->save();
            painter->setPen(pen_);
            painter->setBrush(brush_);
            painter->drawRect(option->rect.adjusted(0, 0, -1, -1));
            painter->restore();
            return;
        }

        base_type::drawControl(element, option, painter, widget);
    }

private:
    QPen pen_;
    QBrush brush_;
};

使用方式

    //橡皮筋的风格设置 ********************************
    QPen pen(QBrush(Qt::red), 0, Qt::DotLine);
    QBrush brush(Qt::transparent);
    auto rubberbandStyle = new RubberbandStyle(pen, brush, nullptr);
    rubberbandStyle->setParent(this);
    viewport()->setStyle(rubberbandStyle);
    //橡皮筋的风格设置 ********************************

源码分析:QGraphicsView的paintEvent中:

#if QT_CONFIG(rubberband)
    // Rubberband
    if (d->rubberBanding && !d->rubberBandRect.isEmpty()) {
        painter.restore();
        QStyleOptionRubberBand option;
        option.initFrom(viewport());
        option.rect = d->rubberBandRect;
        option.shape = QRubberBand::Rectangle;

        QStyleHintReturnMask mask;
        if (viewport()->style()->styleHint(QStyle::SH_RubberBand_Mask, &option, viewport(), &mask)) {
            // painter clipping for masked rubberbands
            painter.setClipRegion(mask.region, Qt::IntersectClip);
        }

        viewport()->style()->drawControl(QStyle::CE_RubberBand, &option, &painter, viewport());
    }
#endif

QWindowsXPStyle::drawControl中的源码：

#if QT_CONFIG(rubberband)
    case CE_RubberBand:
        if (qstyleoption_cast<const QStyleOptionRubberBand *>(option)) {
            QColor highlight = option->palette.color(QPalette::Active, QPalette::Highlight);
            p->save();
            p->setPen(highlight.darker(120));
            QColor dimHighlight(qMin(highlight.red()/2 + 110, 255),
                                qMin(highlight.green()/2 + 110, 255),
                                qMin(highlight.blue()/2 + 110, 255),
                                (widget && widget->isTopLevel())? 255 : 127);
            p->setBrush(dimHighlight);
            p->drawRect(option->rect.adjusted(0, 0, -1, -1));
            p->restore();
            return;
        }
        break;
#endif // QT_CONFIG(rubberband)