1.概要
2.代码
在Qt中,如果你想要创建一个矩形,并且仅允许通过拖拽其左侧边线来改变宽度,你可以通过重写QGraphicsRectItem
类来实现。以下是一个简单的例子,展示了如何创建一个自定义的ResizableRectItem
类,该类允许用户通过拖拽矩形的左侧边线来改变其宽度:
#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsRectItem>
#include <QMouseEvent>
#include <QPointF>
#include <QSizeF>
#include <QRectF>
#include <QGraphicsSceneMouseEvent>class ResizableRectItem : public QGraphicsRectItem {
public: ResizableRectItem(const QRectF &rect, QGraphicsItem *parent = nullptr) : QGraphicsRectItem(rect, parent), dragging(false), dragStartWidth(0.0), dragStartPos(QPointF()) {} protected: void mousePressEvent(QGraphicsSceneMouseEvent *event) override { if (event->button() == Qt::LeftButton) { QRectF rect = this->rect(); QPointF pos = event->pos(); const int edgeSensitivity = 5; // Pixels if (qAbs(pos.x() - rect.x()) < edgeSensitivity) { // Left edge dragging = true; dragStartWidth = rect.width(); dragStartPos = pos; } } //QGraphicsRectItem::mousePressEvent(event); } void mouseMoveEvent(QGraphicsSceneMouseEvent *event) override { if (dragging) { QPointF pos = event->pos(); qreal newWidth = dragStartWidth - (dragStartPos.x() - pos.x()); this->setRect(QRectF(pos.x(), this->rect().y(), newWidth, this->rect().height())); } //QGraphicsRectItem::mouseMoveEvent(event); } void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) override { dragging = false; QGraphicsRectItem::mouseReleaseEvent(event); } private: bool dragging; qreal dragStartWidth; QPointF dragStartPos;
}; class MainWindow : public QGraphicsView {
public: MainWindow(QWidget *parent = nullptr) : QGraphicsView(parent) { QGraphicsScene *scene = new QGraphicsScene(this); this->setScene(scene); ResizableRectItem *rect = new ResizableRectItem(QRectF(10, 10, 200, 100)); scene->addItem(rect); }
}; int main(int argc, char *argv[]) { QApplication app(argc, argv); MainWindow window; window.resize(400, 300); window.show(); return app.exec();
}
在这个例子中,ResizableRectItem
类重写了mousePressEvent
、mouseMoveEvent
和mouseReleaseEvent
方法。当用户点击矩形的左侧边线时,mousePressEvent
会设置拖拽状态,并记录拖拽开始时的宽度和位置。当用户移动鼠标时,mouseMoveEvent
会根据鼠标的新位置更新矩形的宽度。最后,当用户释放鼠标按钮时,mouseReleaseEvent
会结束拖拽状态。
代码2
#include <QApplication>
#include <QMainWindow>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsRectItem>
#include <QMouseEvent>
#include <QGraphicsSceneMouseEvent>//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
class DraggableRectItem : public QGraphicsRectItem {
public:DraggableRectItem(const QRectF &rect, QGraphicsItem *parent = nullptr): QGraphicsRectItem(rect, parent),dragging(false) {}protected:void mousePressEvent(QGraphicsSceneMouseEvent *event) override {if (event->button() == Qt::LeftButton) {dragging = true;lastPos = event->pos();}//QGraphicsRectItem::mousePressEvent(event);}void mouseMoveEvent(QGraphicsSceneMouseEvent *event) override {if (dragging) {QRectF rect = this->rect();QPointF diff = event->pos() - lastPos;rect.translate(diff);this->setRect(rect);lastPos = event->pos();}//QGraphicsRectItem::mouseMoveEvent(event);}void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) override {dragging = false;//QGraphicsRectItem::mouseReleaseEvent(event);}private:bool dragging;QPointF lastPos;
};class MainWindow : public QMainWindow {
public:MainWindow(QWidget *parent = nullptr) : QMainWindow(parent) {auto *scene = new QGraphicsScene(this);auto *view = new QGraphicsView(scene, this);setCentralWidget(view);auto *rect = new DraggableRectItem(QRectF(10, 10, 200, 100));scene->addItem(rect);}
};int main(int argc, char *argv[]) {QApplication app(argc, argv);MainWindow window;window.resize(400, 300);window.show();return app.exec();
}