QT QGraphicsView实现预览图片显示缩略图功能QT creator Qt5.15.2

头文件：

#ifndef TGRAPHICSVIEW_H
#define TGRAPHICSVIEW_H#include <QGraphicsView>
#include <QMainWindow>
#include <QObject>
#include <QWidget>class TGraphicsView : public QGraphicsView
{Q_OBJECT
public:TGraphicsView(QWidget *parent = 0);
private slots:void scrollBarValueChanged();private:void resizeEvent(QResizeEvent *event) override;void updateThumbRoi();struct PosInfo{int min;int max;int value;int page;};private:class Thumb;Thumb *thumb;
};
class TGraphicsView::Thumb : public QWidget
{Q_OBJECTpublic:using PosInfo = TGraphicsView::PosInfo;Thumb(QWidget* parent = 0);void updateImage();void updateRoi(const PosInfo& xinfo, const PosInfo& yinfo);private:void paintEvent(QPaintEvent *event) override;private:QPixmap background;QRect roi;
};#endif // TGRAPHICSVIEW_H

 cpp文件：

TGraphicsView::TGraphicsView(QWidget *parent) :QGraphicsView(parent)
{thumb = new Thumb(this);QScrollBar* hsb = horizontalScrollBar();connect(hsb, &QScrollBar::valueChanged, this, &TGraphicsView::scrollBarValueChanged);QScrollBar* vsb = verticalScrollBar();connect(vsb, &QScrollBar::valueChanged, this, &TGraphicsView::scrollBarValueChanged);}void TGraphicsView::resizeEvent(QResizeEvent *event)
{QGraphicsView::resizeEvent(event);thumb->updateImage();updateThumbRoi();
}void TGraphicsView::scrollBarValueChanged()
{updateThumbRoi();
}void TGraphicsView::updateThumbRoi()
{QScrollBar* hsb = horizontalScrollBar();PosInfo xinfo;xinfo.min = hsb->minimum();xinfo.max = hsb->maximum();xinfo.value = hsb->value();xinfo.page = hsb->pageStep();QScrollBar* vsb = verticalScrollBar();PosInfo yinfo;yinfo.min = vsb->minimum();yinfo.max = vsb->maximum();yinfo.value = vsb->value();yinfo.page = vsb->pageStep();thumb->updateRoi(xinfo, yinfo);
}/TGraphicsView::Thumb::Thumb(QWidget* parent) :QWidget(parent)
{setFixedSize(150, 150);
}void TGraphicsView::Thumb::paintEvent(QPaintEvent *)
{QPainter painter(this);painter.setOpacity(0.8);painter.fillRect(QRect(0, 0, width(), height()), QColor(255, 192, 32));int xoff = (width() - background.width()) / 2;int yoff = (height() - background.height()) / 2;painter.drawPixmap(xoff, yoff, background);/* 绘制ROI *///painter.setPen(QColor(32, 32, 32));painter.setPen(QColor(255, 0, 0));painter.setBrush(Qt::NoBrush);painter.drawRect(roi.adjusted(xoff, yoff, xoff, yoff));
}void TGraphicsView::Thumb::updateImage()
{QGraphicsView* view = dynamic_cast<QGraphicsView*>(parent());QRectF rect = view->sceneRect();qreal ratio = qMin(width() / rect.width(), height() / rect.height());background = QPixmap(rect.width() * ratio, rect.height() * ratio);QPainter painter(&background);QGraphicsScene* sc = view->scene();sc->render(&painter);update();
}void TGraphicsView::Thumb::updateRoi(const PosInfo& xinfo, const PosInfo& yinfo)
{int w = background.width();int xwhole = ((xinfo.max - xinfo.min) + xinfo.page);int roiLeft = w * xinfo.value / xwhole;int roiWidth = w * xinfo.page / xwhole;int h = background.height();int ywhole = ((yinfo.max - yinfo.min) + yinfo.page);int roiTop = h * yinfo.value / ywhole;int roiHeight = h * yinfo.page / ywhole;roi = QRect(roiLeft, roiTop, roiWidth, roiHeight);update();
}

工程代码：

https://download.csdn.net/download/txwtech/89700311