The infamous "deleted graphics item reappears" bug is present in my app, how do I fix it?

enjoysmath

That is the symptom pictured above. As you can see, those arrows will reappear, in particular when I'm dragging an object over them, and sometimes I believe when an arrow gets deleted but it's still attached to something.

Anyway, what is a design pattern that I can use for a DeleteUndoCmd? I.e. whatever the deletion does, it must be undoable which means re-attaching arrows to nodes if need be.

Anyway, I know about all that and coded my app robustly and even used a deleteLater() in there somewhere. However, as you can see items are not actually being removed from the scene (deleted).

The PyQt5 code can be found here: https://github.com/enjoysmath/abstract-spacecraft

Anyway, before I tackle this bug, I would like to know the proper / the only way to really delete something in a PyQt5 QGraphcisScene.

enjoysmath

Nevermind! Modifying DeleteItems with a _connectivity dictionary seems to have solved the problem.

class DeleteItems(UndoCmd):
    Parent, Source, Dest = range(3)
    
    def __init__(self, items:list, canvas:LanguageCanvas):
        super().__init__()
        self._items = items
        self._canvas = canvas
        self._connectivity = {}
        
    def redo(self):
        for item in self._items:
            if isinstance(item, Arrow):
                self._connectivity[id(item)] = (item.parentItem(), item.source, item.destination)                
                item.set_source(None)
                item.set_destination(None)
            elif isinstance(item, (Object, Text)):
                self._connectivity[id(item)] = item.parentItem()
            item.setParentItem(None)
            self._canvas.removeItem(item)
            
    def undo(self):
        for item in self._items:
            if isinstance(item, Arrow):
                parent, source, dest = self._connectivity[id(item)]
                item.set_source(source)
                item.set_destination(dest)
            elif isinstance(item, (Object, Text)):
                parent = self._connectivity[id(item)]
            item.setParentItem(parent)
            self._canvas.addItem(item)

I honestly thought this would be much tougher to fix.