Using Signals in QGraphicsItem
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@adrien-lsh
I think it is to do with the initialisation, requiring both inherited classes to be initialised. You were only doing so for theQGraphicsLineItem, not initialising theQObject. I find the following does work without crashing:class CroppingLine(QObject, QGraphicsLineItem): moved = Signal(object, QPointF) def __init__(self, x1: float, y1: float, x2: float, y2: float): #super(QGraphicsLineItem, self).__init__(x1, y1, x2, y2) QObject.__init__(self) QGraphicsLineItem.__init__(self, x1, y1, x2, y2)There may be other ways of doing this with
super()and/or not swapping the inheritance order, I just know this works fine.wrote on 25 Feb 2025, 10:03 last edited by@JonB
Of course ! It never initialized theQObjectso signals would never work.
Thank you for your help ! -
Hi,
It's Python3, remove the class from your super calls. This should allow Python to do proper initialisation of the chain of classes (though sometimes it might fail for complex cases).
[Edit: we are in such a complex case]
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Hi,
It's Python3, remove the class from your super calls. This should allow Python to do proper initialisation of the chain of classes (though sometimes it might fail for complex cases).
[Edit: we are in such a complex case]
wrote on 25 Feb 2025, 10:27 last edited by JonB@SGaist
But the OP started with justsuper().__init__(x1, y1, x2, y2)and, for whatever reason, that segments (later, on signal emit) because the
QObjectpart has not been initialized, apparently. That is why I tried splitting it into two separate explicit initializations, which makes it work. So what exactly are you proposing? -
@SGaist
But the OP started with justsuper().__init__(x1, y1, x2, y2)and, for whatever reason, that segments (later, on signal emit) because the
QObjectpart has not been initialized, apparently. That is why I tried splitting it into two separate explicit initializations, which makes it work. So what exactly are you proposing?@JonB I misread the code !
We are in the territory where your solution (using
__init__) is the way to go. Multiple inheritance in Python is quite tricky...QObject expects an optional parent parameter which is not given here but it's not expecting the parameters for the QGraphicsLineItem constructor hence the failure. You can try to use the kwargs trick however it won't work either as it's not part of any of the method signature and thus can't work either.
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wrote on 25 Feb 2025, 20:02 last edited by NlightThis post is deleted!
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