Question

我正在开发一个Qt项目。必须在Qpainter区域上单击鼠标绘制一个点。点位置应该位于鼠标点击的同一个精确位置，但由于某种原因，该点被绘制在与预期位置成对角线的另一个位置。

代码：

MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent), ui(new Ui::MainWindow)
{
QGraphicsView * view = new QGraphicsView(this) ;
ui->setupUi(this);
QGridLayout * gridLayout = new QGridLayout(ui->centralWidget);
gridLayout->addWidget(view);

scene = new QGraphicsScene();
scene->setSceneRect(50, 50, 350, 350);

view->setScene(scene);
} 

void MainWindow::mousePressEvent(QMouseEvent * e)
{
 QGraphicsView * view = new QGraphicsView(this) ;
 double rad = 1;
 QPointF pt = view->mapToScene(e->pos());
 scene->addEllipse(pt.x()-rad, pt.y()-rad, rad*2.0, rad*2.0,QPen(),  QBrush(Qt::SolidPattern));
}

Answer 1

您的代码不正确。每次点击都会创建沉重的视图，不应该这样做。如果您希望该用户能够与场景交互，则创建新的自定义场景并在场景中执行您需要的所有帽子。

#ifndef GRAPHICSSCENE_H
#define GRAPHICSSCENE_H

#include <QGraphicsScene>
#include <QPoint>
#include <QMouseEvent>
class GraphicsScene : public QGraphicsScene
{
    Q_OBJECT
public:
    explicit GraphicsScene(QObject *parent = 0);
    ~GraphicsScene();

signals:

protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event);
public slots:
    private:

};

#endif // GRAPHICSSCENE_H

CPP：

#include "graphicsscene.h"
#include <QDebug>

GraphicsScene::GraphicsScene(QObject *parent) :
    QGraphicsScene(parent)
{
}

GraphicsScene::~GraphicsScene()
{
    qDebug() << "deleted scene";
}


void GraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
{

      if (mouseEvent->button() == Qt::LeftButton)
      {
          double rad = 1;
          QPointF pt = mouseEvent->scenePos();
          this->addEllipse(pt.x()-rad, pt.y()-rad, rad*2.0, rad*2.0,QPen(),
          QBrush(Qt::SolidPattern));
      }

    QGraphicsScene::mousePressEvent(mouseEvent);
}

用法，例如：

#include "graphicsscene.h"
//...
GraphicsScene *scene = new GraphicsScene(this);
someview->setScene(scene);

使用Qt在鼠标点击的确切位置绘制一个点

1 个答案: