[Interest] QGraphicsItem does not become a mouse grabber

[Dmitrii Volosnykh]

I'd like my custom item to become an explicit mouse grabber on mouse press
event. I call grabMouse() inside mousePressEvent() handler, but it does not
receive any consecutive mouse move and release events (imagine, I try to
drag this item).

As far as I can see from QGraphicsScene's sources
QGraphicsScenePrivate::mousePressEventHandler() forwards mouse press event
to the item under cursor, making it implicit mouse grabber a priori. After
this mouse event was handled by the target item, the former one releases
mouse grabber state. While in general this seems to be okay, I expect this
custom item to keep mouse grabber state when it was set explicitly. Indeed,
what actually grabMouse() does, being called from mousePressEvent(), is
updates lastMouseGrabberItemHasImplicitMouseGrab flag to false. So, I
guess, ungrabMouse() should be called only in case item is still an
implicit mouse grabber.

Does this suggestion make sense? Should the current behaviour be considered
as a false one?

Regards,
Dmitrii.
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