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    <p>You're not telling us at all what is it that you're trying to do. The Qt's graphics scene / view system is powerful enough to support dragging of items without you having to write any code to handle low-level mouse events. If that's what you're after, that is.</p> <p>Your mouse move event is not called because your mouse press doesn't happen in your widget, but in the child <code>QGraphicsScene</code>. Mouse presses that happen in children will not trigger mouse tracking within your widget.</p> <p>Had you added a layout to manage the child widgets in your Painter class, you'd notice that your mouse move events are handled if you click in the margin outside of the <code>QGraphicsView</code>. The code below shows how to do set a layout on a widget containing a scene view.</p> <p>The code below is a complete and hopefully correct example of creating randomly sized, moveable and focuseable circles. It demonstrates as well:</p> <ul> <li>How to properly map coordinates from the parent widget to scene itself.</li> <li>That clearing the scene does not require manually keeping track of items.</li> <li>How to derive from a predefined item to add simple functionality.</li> <li>How to operate on an item that has focus.</li> <li>That the scene is notified when its children are removed, thus simply deleting a child item is perfectly safe thing to do.</li> <li>That <code>delete</code> safely ignores null pointers, such as potentially returned by <code>QGraphicsScene::focusItem()</code>.</li> <li>How to use object names to automatically attach slots named <code>on_name_signal</code>.</li> <li>How to have Q_OBJECT classes within .cpp files by including the .moc file at the end.</li> <li>How to keep members by value, relegating memory management to the compiler.</li> </ul> <p>The example is self contained and consists of just one .pro and .cpp file each. It works under both Qt 4 and Qt 5, and leverages C++11.</p> <p><img src="https://i.stack.imgur.com/TdkNV.png" alt="screnshot from running the example code"></p> <pre><code>// https://github.com/KubaO/stackoverflown/tree/master/questions/scene-movable-circles-11188261 // main.cpp #include &lt;QtGui&gt; #if QT_VERSION &gt;= QT_VERSION_CHECK(5,0,0) #include &lt;QtWidgets&gt; #endif #include &lt;cmath&gt; class Circle : public QGraphicsEllipseItem { QBrush m_inBrush{Qt::red}, m_outBrush{Qt::lightGray}; public: Circle(const QPointF &amp; c) { const qreal r = 10.0 + (50.0*qrand())/RAND_MAX; setRect({c.x()-r, c.y()-r, 2.0*r, 2.0*r}); setFlag(QGraphicsItem::ItemIsMovable); setFlag(QGraphicsItem::ItemIsFocusable); setPen({Qt::red}); setBrush(m_outBrush); } void focusInEvent(QFocusEvent *) override { setBrush(m_inBrush); } void focusOutEvent(QFocusEvent *) override { setBrush(m_outBrush); } }; class Painter : public QWidget { Q_OBJECT QGridLayout m_layout{this}; QGraphicsView m_view; QPushButton m_clear{"Clear"}; QPushButton m_remove{"Remove"}; QGraphicsScene m_scene; public: explicit Painter(QWidget *parent = nullptr); protected: Q_SLOT void on_remove_clicked(); void mousePressEvent(QMouseEvent *event) override; }; Painter::Painter(QWidget *parent) : QWidget(parent) { m_layout.addWidget(&amp;m_view, 0, 0, 1, 2); m_layout.addWidget(&amp;m_clear, 1, 0); m_layout.addWidget(&amp;m_remove, 1, 1); m_remove.setObjectName("remove"); QMetaObject::connectSlotsByName(this); connect(&amp;m_clear, SIGNAL(clicked()), &amp;m_scene, SLOT(clear())); m_view.setRenderHint(QPainter::Antialiasing); m_view.setScene(&amp;m_scene); m_view.setSceneRect(0,0,500,500); } void Painter::mousePressEvent(QMouseEvent *event) { auto center = m_view.mapToScene(m_view.mapFromParent(event-&gt;pos())); m_scene.addItem(new Circle(center)); } void Painter::on_remove_clicked() { delete m_scene.focusItem(); } int main(int argc, char ** argv) { QApplication app{argc, argv}; Painter p; p.show(); return app.exec(); } #include "main.moc" </code></pre> <pre><code># scene-movable-circles-11188261.pro greaterThan(QT_MAJOR_VERSION, 4) { QT = widgets CONFIG += c++11 } else { QT = gui unix:QMAKE_CXXFLAGS += -std=c++11 macx { QMAKE_CXXFLAGS += -stdlib=libc++ QMAKE_MACOSX_DEPLOYMENT_TARGET = 10.7 QMAKE_CXXFLAGS_WARN_ON += -Wno-inconsistent-missing-override } } DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x050800 TARGET = scene-movable-circles-11188261 TEMPLATE = app SOURCES += main.cpp </code></pre>
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