mouse click in QGprahicsScene

[Bitto]

The correct way to do this is to first call the scene's event handler, and then check if the mouse event was accepted or ignored by the scene.

Reimplement mousePressEvent in QGraphicsScene like this:

void CustomScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    // First check if any items on the scene accept the event
    QGraphicsScene::mousePressEvent(event);
 
    if (!event->isAccepted()) {
        // Someone clicked outside an item, or on an item that doesn't
        // accept mouse events.
    }
}

void CustomScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    // First check if any items on the scene accept the event
    QGraphicsScene::mousePressEvent(event);

    if (!event->isAccepted()) {
        // Someone clicked outside an item, or on an item that doesn't
        // accept mouse events.
    }
}

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This is better than checking if there are items at the mouse position with QGraphicsScene::items(), because certain items are transparent for mouse events. Like landscape items, in a game scene.

[aamer4yu]

What about View ? if we handle the mouse press event in view rather than scene , which one is better ??

Hope i am making sense

[Bitto]

Sure, you can do the same thing in the view, but it's better to handle events for the scene. The view's responsibility is to visualize and navigate the scene. If you handle events in the scene, you can use standard views and still get the correct mouse behavior.

[aamer4yu]

Ok fine..
but how do I check if the Drag event originated from the scene ? I had implemented things in scene itself, but got stuck when I had to check if it originated from the scene.
Because in Scene event, the source() is widget which u have to set at the time of Drag.

[Bitto]

Well all Graphics Scene events come with a widget, and the widget is the originator of the event. So if you want to know what widget started the drag, just pull it out from, for example, the QGraphicsSceneMouseEvent that starts the drag.

void MyItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    // event->widget() is the originating widget, and also the viewport
    // of the originating QGraphicsView. So event->widget()-parentWidget()
    // gives you the view.
}

void MyItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    // event->widget() is the originating widget, and also the viewport
    // of the originating QGraphicsView. So event->widget()-parentWidget()
    // gives you the view.
}

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[aamer4yu]

Actually I wanted to check if the Drag started from this scene or not..

in

MyScene::mousePressEvent(..)
{
     // Start drag
}
 
 
MyScene::dropEvent(QGraphicsSceneDragDropEvent * event )
{
// How to check if this event started from this scene or some other scene..
// how can I compare if(this == event->widget()) ??
 
}

MyScene::mousePressEvent(..)
{
     // Start drag
}


MyScene::dropEvent(QGraphicsSceneDragDropEvent * event )
{
// How to check if this event started from this scene or some other scene..
// how can I compare if(this == event->widget()) ??

}

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Also i guess if i am starting the drag in scene, I have to handle all the move events and setting of position of item in the scene.. right ??

[Bitto]

You know the view, so you can easily ask for the scene:

QWidget *viewport = event->widget();
QGraphicsView *view = viewport ? qobject_cast<QGraphicsView *>(viewport->parentWidget()) : 0;
 
QGraphicsScene *scene = view->scene();

QWidget *viewport = event->widget();
QGraphicsView *view = viewport ? qobject_cast<QGraphicsView *>(viewport->parentWidget()) : 0;

QGraphicsScene *scene = view->scene();

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