在Qt中,要创建一个左侧边线可以向左侧拖拽的矩形,你需要自定义一个QGraphicsRectItem
的子类,并处理鼠标事件来实现拖拽功能。以下是一个简单的实现:
#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsRectItem>
#include <QMouseEvent>
class ResizableRectItem : public QGraphicsRectItem {
public:
ResizableRectItem(const QRectF &rect, QGraphicsItem *parent = nullptr)
: QGraphicsRectItem(rect, parent),
dragging(false),
edgeSensitivity(5) {}
protected:
void mousePressEvent(QGraphicsSceneMouseEvent *event) override {
if (event->button() == Qt::LeftButton) {
QRectF rect = this->rect();
QPointF pos = event->pos();
if (pos.x() <= rect.x() + edgeSensitivity) {
// Left edge
dragging = true;
dragStartPos = pos;
}
}
}
void mouseMoveEvent(QGraphicsSceneMouseEvent *event) override {
if (dragging) {
QPointF pos = event->pos();
qreal newX = pos.x();
if (newX < this->rect().x() + this->rect().width()) {
// Prevent the rectangle from becoming too small or negative width
this->setRect(QRectF(newX, this->rect().y(), this->rect().x() + this->rect().width() - newX, this->rect().height()));
}
}
}
void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) override {
dragging = false;
}
private:
bool dragging;
QPointF dragStartPos;
int edgeSensitivity;
};
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QGraphicsScene scene;
QGraphicsView view(&scene);
ResizableRectItem *rect = new ResizableRectItem(QRectF(50, 50, 200, 100));
scene.addItem(rect);
view.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,并记录拖拽开始的位置。当用户移动鼠标时,mouseMoveEvent
会根据鼠标的新位置更新矩形的位置,实际上是改变矩形的x
坐标,同时保持宽度不变(或者你可以根据需要调整宽度)。最后,当用户释放鼠标按钮时,mouseReleaseEvent
会结束拖拽状态。
注意,在mouseMoveEvent
中,我们检查新的x
坐标是否小于矩形的当前x
坐标加上宽度,这是为了防止矩形变得太小或宽度变为负数。如果新的x
坐标满足这个条件,我们就更新矩形的位置。