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I have subclassed
QGraphicsRectItem
, and it's not receiving any mouse events. I've seen other questions similar to this say I need to enable mouse tracking, but
setMouseTracking
is in QWidget, and QGraphicsItem does not appear to be a QWidget.
I've implemented
paint
, and that's working. In my subclassed QGraphicsView I am getting mouse events.
The docs seem to think I should just override the mousePressEvent function (for example) and I should start getting the events. Whether I forward the mousePressEvent to the superclass of my QGraphicsView or not doesn't seem to make any difference.
In your subclassed QGraphicsView, you need to call the default implementations of overridden mouse event methods if you want them to propagate down to the items. For example:
CustomView::mousePressEvent(QMouseEvent *event)
// handle the event as you like
QGraphicsView::mousePressEvent(event); // then call default implementation
If you want to accept hover events, you need to call QGraphicsItem::setAcceptHoverEvents(true);. Otherwise you do not need to enable any particular mouse tracking.
EDIT: Here is a full working example:
#include <QtGui>
class CustomView : public QGraphicsView
protected:
void mousePressEvent(QMouseEvent *event)
qDebug() << "Custom view clicked.";
QGraphicsView::mousePressEvent(event);
class CustomItem : public QGraphicsRectItem
protected:
void mousePressEvent(QGraphicsSceneMouseEvent *event)
qDebug() << "Custom item clicked.";
int main(int argc, char *argv[])
QApplication a(argc, argv);
CustomItem item;
item.setRect(20, 20, 60, 60);
QGraphicsScene scene(0, 0, 100, 100);
scene.addItem(&item);
CustomView view;
view.setScene(&scene);
view.show();
return a.exec();
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I went through the same problems you have encountered and I wanted to add some insights on top of Anthony's really good answer. Here is an example I wrote showing some features that can be implemented using the mouse events and the keyboard events.
Note that the events do not propagate to QGraphicsItems in a QGraphicsItemGroup or in a QList<QGraphicsItem> (it took me a while to figure that out).
#include <QtGui>
#include <QGraphicsRectItem>
#include <QGraphicsView>
#include <QApplication>
#include <QGraphicsSceneMouseEvent>
class CustomItem : public QGraphicsEllipseItem
protected:
void mousePressEvent(QGraphicsSceneMouseEvent *event)
if(event->button() == Qt::LeftButton) {
if(event->modifiers() == Qt::ShiftModifier) {
qDebug() << "Custom item left clicked with shift key.";
// add the item to the selection
setSelected(true);
} else if(event->modifiers() == Qt::AltModifier){
qDebug() << "Custom item left clicked with alt key.";
// resize the item
double radius = boundingRect().width() / 2.0;
_center = QPointF(boundingRect().topLeft().x() + pos().x() + radius, boundingRect().topLeft().y() + pos().y() + radius);
QPointF pos = event->scenePos();
qDebug() << boundingRect() << radius << this->pos() << pos << event->pos();
double dist = sqrt(pow(_center.x()-pos.x(), 2) + pow(_center.y()-pos.y(), 2));
if(dist / radius > 0.8) {
qDebug() << dist << radius << dist / radius;
_isResizing = true;
} else {
_isResizing = false;
} else {
qDebug() << "Custom item left clicked.";
QGraphicsItem::mousePressEvent(event);
event->accept();
} else if(event->button() == Qt::RightButton) {
qDebug() << "Custom item right clicked.";
event->ignore();
void mouseMoveEvent(QGraphicsSceneMouseEvent *event)
if(event->modifiers() == Qt::AltModifier && _isResizing){
QPointF pos = event->scenePos();
double dist = sqrt(pow(_center.x()-pos.x(), 2) + pow(_center.y()-pos.y(), 2));
setRect(_center.x()-this->pos().x()-dist, _center.y()-this->pos().y()-dist, dist*2, dist*2);
} else if(event->modifiers() != Qt::AltModifier) {
qDebug() << "Custom item moved.";
QGraphicsItem::mouseMoveEvent(event);
qDebug()<<"moved"<<pos();
void mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
if(event->modifiers() == Qt::AltModifier && _isResizing) {
_isResizing = false;
} else if(event->modifiers() != Qt::ShiftModifier) {
QGraphicsItem::mouseReleaseEvent(event);
int type() const
// Enable the use of qgraphicsitem_cast with this item.
return UserType+1;
private:
QPointF _center;
bool _isResizing;
class CustomScene : public QGraphicsScene
protected:
void mousePressEvent(QGraphicsSceneMouseEvent *event)
qDebug() << "Custom scene clicked.";
QGraphicsScene::mousePressEvent(event);
if(!event->isAccepted()) {
if(event->button() == Qt::LeftButton) {
// add a custom item to the scene
QPointF pt = event->scenePos();
CustomItem * item = new CustomItem();
item->setRect(pt.x()-25, pt.y()-25, 50, 50);
item->setFlags(QGraphicsItem::ItemIsSelectable|
QGraphicsItem::ItemIsMovable);
addItem(item);
} else if(event->button() == Qt::RightButton) {
// check whether there is an item under the cursor
QGraphicsItem * itemToRemove = NULL;
foreach(auto item, items(event->scenePos())) {
if(item->type() == QGraphicsItem::UserType+1) {
itemToRemove = item;
break;
if(itemToRemove) {
// remove the item from the graphicsScene
removeItem(itemToRemove);
void mouseMoveEvent(QGraphicsSceneMouseEvent *event)
qDebug() << "Custom scene moved.";
QGraphicsScene::mouseMoveEvent(event);
void keyPressEvent(QKeyEvent * event) {
if(event->key() == Qt::Key_Backspace) {
// remove all selected items
qDebug() << "selected items" << selectedItems().size();
while(!selectedItems().isEmpty()) {
removeItem(selectedItems().front());
} else {
QGraphicsScene::keyPressEvent(event);
int main(int argc, char *argv[])
QApplication a(argc, argv);
CustomItem item;
item.setRect(20, 20, 60, 60);
item.setFlags(QGraphicsItem::ItemIsSelectable|
QGraphicsItem::ItemIsMovable);
CustomScene scene;
scene.setSceneRect(0, 0, 500, 500);
scene.addItem(&item);
QGraphicsView view;
view.setScene(&scene);
view.show();
return a.exec();
Hope it helps too!
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