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copied!<p>UPDATE: There is a new class called <code>QGraphicsSceneMouseEvent</code> that makes this a little easier. I just finished an example using it here:</p> <p><a href="https://stackoverflow.com/a/26903599/999943">https://stackoverflow.com/a/26903599/999943</a></p> <p>It differs with the answer below in that it subclasses <code>QGraphicsScene</code>, not <code>QGraphicsView</code>, and it uses <code>mouseEvent->scenePos()</code> so there isn't a need to manually map coordinates.</p> <hr> <p>You are on the right track, but you still have a little more to go.</p> <p>You need to subclass <code>QGraphicsView</code> to be able to do something with mouse presses or with mouse releases using <code>QMouseEvent</code>.</p> <pre><code> #include <QGraphicsView> #include <QGraphicsScene> #include <QGraphicsEllipseItem> #include <QMouseEvent> class MyQGraphicsView : public QGraphicsView { Q_OBJECT public: explicit MyQGraphicsView(QWidget *parent = 0); signals: public slots: void mousePressEvent(QMouseEvent * e); // void mouseReleaseEvent(QMouseEvent * e); // void mouseDoubleClickEvent(QMouseEvent * e); // void mouseMoveEvent(QMouseEvent * e); private: QGraphicsScene * scene; }; </code></pre> <p><code>QGraphicsView</code> doesn't natively have dimension-less points. You will probably want to use <code>QGraphicsEllipse</code> item or simply, <code>scene->addEllipseItem()</code> with a very small radius.</p> <pre><code> #include "myqgraphicsview.h" #include <QPointF> MyQGraphicsView::MyQGraphicsView(QWidget *parent) : QGraphicsView(parent) { scene = new QGraphicsScene(); this->setSceneRect(50, 50, 350, 350); this->setScene(scene); } void MyQGraphicsView::mousePressEvent(QMouseEvent * e) { double rad = 1; QPointF pt = mapToScene(e->pos()); scene->addEllipse(pt.x()-rad, pt.y()-rad, rad*2.0, rad*2.0, QPen(), QBrush(Qt::SolidPattern)); } </code></pre> <p>Note the usage of <code>mapToScene()</code> to make the <code>pos()</code> of the event map correctly to where the mouse is clicked on the scene.</p> <p>You need to add an instance of your subclassed <code>QGraphicsView</code> to the centralWidget's layout of your ui if you are going to use a form. </p> <pre><code> QGridLayout * gridLayout = new QGridLayout(ui->centralWidget); gridLayout->addWidget( new MyQGraphicsView() ); </code></pre> <p>or if your ui has a layout already it will look like this:</p> <pre><code> ui->centralWidget->layout()->addWidget( new MyGraphicsView() ); </code></pre> <p>If you don't use a <code>QMainWindow</code> and a form, you can add it to a <code>QWidget</code> if you set a layout for it and then add your <code>QGraphicsView</code> to that layout in a similar manner. If you don't want a margin around your <code>QGraphicsView</code>, just call show on it and don't put it inside a different layout.</p> <pre><code> #include <QtGui/QApplication> #include "myqgraphicsview.h" int main(int argc, char *argv[]) { QApplication a(argc, argv); MyQGraphicsView view; view.show(); return a.exec(); } </code></pre> <p>And that's it. Now you are dangerous with <code>QGraphicsView</code>'s and their interaction with the mouse.</p> <p>Be sure to read and study about Qt's <a href="https://doc.qt.io/qt-5/graphicsview.html" rel="nofollow noreferrer">Graphics View Framework</a> and the related <a href="https://doc.qt.io/qt-5/examples-graphicsview.html" rel="nofollow noreferrer">examples</a> to be effective when using <code>QGraphicsView</code> and <code>QGraphicsScene</code>. They are very powerful tools for 2D graphics and can have a bit of a learning curve but they are worth it.</p>

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