1.概要

需求，一个可以拖拽的矩形，鼠标接近边线点击变成可拖拽形状。

2.代码

#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsRectItem>
#include <QMouseEvent>
#include <QGraphicsSceneMouseEvent>
#include <QLabel>
//https://blog.csdn.net/xie__jin__cheng/article/details/140438674?spm=1001.2014.3001.5501
//qt 创建一个矩形，矩形的边线可以拖拽，拖拽时这个矩形随着这个边线缩放
class ResizableRectItem : public QGraphicsRectItem {
public:
    ResizableRectItem(const QRectF &rect, QGraphicsItem *parent = nullptr)
        : QGraphicsRectItem(rect, parent),
        dragging(false),
        dragStartSize(QSizeF()),
        dragStartPos(QPointF()) {}

protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event) override {
        if (event->button() == Qt::LeftButton) {
            // Check if the mouse click is close to any of the rectangle's edges
            QRectF rect = this->rect();
            QPointF pos = event->pos();
            QSizeF size = rect.size();
            const int edgeSensitivity = 5; // Pixels

            if (qAbs(pos.x() - rect.x()) < edgeSensitivity) {
                setCursor(Qt::SizeHorCursor);
                // Left edge
                dragging = true;
                dragStartSize = size;
                dragStartPos = pos;
                currentEdge = LeftEdge;
            } else if (qAbs(pos.x() - (rect.x() + rect.width())) < edgeSensitivity) {
                setCursor(Qt::SizeHorCursor);
                // Right edge
                dragging = true;
                dragStartSize = size;
                dragStartPos = pos;
                currentEdge = RightEdge;
            } else if (qAbs(pos.y() - rect.y()) < edgeSensitivity) {
                setCursor(Qt::SizeVerCursor);
                // Top edge
                dragging = true;
                dragStartSize = size;
                dragStartPos = pos;
                currentEdge = TopEdge;
            } else if (qAbs(pos.y() - (rect.y() + rect.height())) < edgeSensitivity) {
                setCursor(Qt::SizeVerCursor);
                // Bottom edge
                dragging = true;
                dragStartSize = size;
                dragStartPos = pos;
                currentEdge = BottomEdge;
            }
        }
        //QGraphicsRectItem::mousePressEvent(event);
    }

    void mouseMoveEvent(QGraphicsSceneMouseEvent *event) override {
        if (dragging) {
            QPointF pos = event->pos();
            QSizeF newSize = dragStartSize;

            switch (currentEdge) {
            case LeftEdge:
                newSize.setWidth(dragStartSize.width() - ( pos.x()-dragStartPos.x()));
                this->setRect(QRectF(pos.x(), this->rect().y(), newSize.width(), this->rect().height()));
                break;
            case RightEdge:
                newSize.setWidth(dragStartSize.width() + (pos.x() - dragStartPos.x()));
                this->setRect(QRectF(this->rect().x(), this->rect().y(), newSize.width(), this->rect().height()));
                break;
            case TopEdge:
                newSize.setHeight(dragStartSize.height() - (pos.y() - dragStartPos.y()));
                this->setRect(QRectF(this->rect().x(), pos.y(), this->rect().width(), newSize.height()));
                break;
            case BottomEdge:
                newSize.setHeight(dragStartSize.height() + (pos.y() - dragStartPos.y()));
                this->setRect(QRectF(this->rect().x(), this->rect().y(), this->rect().width(), newSize.height()));
                break;
            }
        }
        //QGraphicsRectItem::mouseMoveEvent(event);
    }

    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) override {
        dragging = false;
        // 鼠标不在线条上，恢复默认光标形状
        setCursor(Qt::ArrowCursor);
        QGraphicsRectItem::mouseReleaseEvent(event);
    }

private:
    bool dragging;
    QSizeF dragStartSize;
    QPointF dragStartPos;
    enum Edge { LeftEdge, RightEdge, TopEdge, BottomEdge };
    Edge currentEdge;
};

class MainWindow : public QGraphicsView {
public:
    MainWindow(QWidget *parent = nullptr) : QGraphicsView(parent) {

        auto *scene = new QGraphicsScene(this);
        this->setScene(scene);

        // 设定原始矩形的参数
        int originalX = 10;
        int originalY = 10;
        int originalWidth = 200;
        int originalHeight = 100;

        auto *rect = new ResizableRectItem(QRectF(originalX, originalY, originalWidth, originalHeight));

        // 计算拆分后的两个矩形的参数
        int spacing = 10;
        int rect1Width = (originalWidth - spacing) / 2;
        int rect2Width = originalWidth - rect1Width - spacing;

        // 创建两个QGraphicsRectItem对象，分别代表拆分后的矩形
        auto* rectItem1 = new ResizableRectItem(QRectF(originalX, originalY, rect1Width, originalHeight));
        auto* rectItem2 = new ResizableRectItem(QRectF(originalX + rect1Width + spacing, originalY, rect2Width, originalHeight));

        // 将拆分后的矩形添加到场景中
        scene->addItem(rectItem1);
        scene->addItem(rectItem2);

        //scene->addItem(rect);

    }
};




int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    MainWindow window;
    window.resize(400, 300);

    window.show();

    return app.exec();
}

3.运行结果