[PyQt] adding signalling to QGraphicsItems

[Christopher M. Nahler]

On 01.07.2010 12:29, Phil Thompson wrote:
> On Thu, 01 Jul 2010 11:58:01 +0200, "Christopher M. Nahler"
> <christopher.nahler at papermodels.at>  wrote:
>    
>> I want to add signalling functionality to scene items. In my case they
>> are usually QGraphicsRectItems..
>>
>> I thought I could do this with deriving from QGraphicsObject but then I
>> loose all the funtionality for the rectangle, handling pens and brushes,
>> shapes etc.
>>
>> Isn't it easier to just derive from QGraphicsRectItem and QObject? Or
>> should I derive from QGraphicsRectItem and QGraphicsObject instead?
>>      
> Neither. You can't multiply inherit from more than one PyQt class.
>
>    
>> Or are there any other ways to do this?
>>      
> Create a QObject subclass that implements your signals as an attribute of
> your QGraphicsRectItem.
>
> Phil
>    

Thanks for the quick reply. I have tried to implement it that way but 
stumbled over another problem I have in this case. I want to announce 
that a MyRectangle was created (or has changed). When I want to add a 
signalling object to my rectangle class I have to def it before. But 
when I define the signal there I have to specify the data type which is 
not yet defined.


#!/usr/bin/env python
# -*- coding: utf-8 -*-

from PyQt4.QtCore import *
from PyQt4.QtGui import *

class Communicator(QObject):
     MyRectangleCreated = pyqtSignal(MyRectangle) <-- MyRectangle not 
defined yet!

     def __init(self):
         super(Communicator, self).__init__(parent)


class MyRectangle(QGraphicsRectItem):

     def __init__(self, rect=QRectF(0, 0, 0, 0), parent=None, scene=None):
         super(MyRectangle, self).__init__(parent, scene)
         self.myCommunicator = Communicator()
         self.myCommunicator.MyRectangleCreated.emit(self)

if __name__ == "__main__":
     r = MyRectangle()

In genereal what I want to do is synchronize the QGraphicsItems from the 
scene with a list of data objects. So when I create a graphics item a 
data object in the data manager should be created and when I change a 
graphics object the corresponding data block object should be updated.

BTW right now I have the handling of the events (which creates and 
changes graphics items) in a widget derived from a view.

Any hints on the best approach for that?

Thanks
Chris
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