[PyQt] QGraphicsPolygonItem / porting from QCanvas to QGraphicsScene

[Michael Krauss]

Hello list members,

i am porting a program from PyQt3 to PyQt4. It formerly used QCanvas
and QCanvasView. Now i am using QGraphicsScene and QGraphicsView.

I replaced QCanvasPolygonalItem with QGraphicsPolygonItem but its
constructor doesn't work as expected.

The old code:

class GuiVertex(QCanvasPolygonalItem):
    '''
    Graphical representation of a vertex
    '''
    def __init__(self, text, canvas):
        QCanvasPolygonalItem.__init__(self, canvas)
[...]
	
The new code:

class GuiVertex(QGraphicsPolygonItem):
    '''
    Graphical representation of a vertex
    '''
    def __init__(self, text, canvas):
        QGraphicsPolygonItem.__init__(self, canvas)
[...]

The error message:

[mickraus at gandalf src]\$ python gui.py   
Traceback (most recent call last):
  File "gui.py", line 420, in <module>
    main()
  File "gui.py", line 414, in main
    gui = Gui()
  File "gui.py", line 343, in __init__
    self.board.addVertex(str(v), x, y)
  File "gui.py", line 221, in addVertex
    vertex = GuiVertex(text, self)
  File "gui.py", line 157, in __init__
    QGraphicsPolygonItem.__init__(self, canvas)
TypeError: argument 1 of QGraphicsPolygonItem() has an invalid type

According to the manual
http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/qgraphicspolygonitem.html
the constructor expects a QGraphicsItem. As GuiVertex is a (sub)^4class
of QGraphicsItem I don't understand the TypeError. The second argument
passed to QGraphicsPolygonItem.__init__ in line 221 is of type 
"class Board(QGraphicsScene)".


Kind regards,
Michael Krauss