[PyQt] Signals/Slots old/new

Vayu vayu at sklinks.com
Sun Jun 24 19:16:03 BST 2012

In trying to send values back and forth from a main window to a docked widget I have questions about what ended up working, especially regarding examples from web searches showing old vs new way.  

Did I do it the best way when using the new way?  And why do I want to use the new way?

I had to create a separate class subclassed from QObject in order to create a signal and specify that it had arguments like this:

class Messenger(QtCore.QObject):    
    fromWidgetSignal = QtCore.pyqtSignal(['QString'])
    fromMainWindowSignal = QtCore.pyqtSignal(['QString'])

Connect and emit like this in the main window:

    self.messageSender = Messenger()

    self.messageSender.fromMainWindowSignal.emit("Main Window sends a value.")  

and the widget needed to receive the new message class as a parameter to send:
    def __init__(self, messageSender):      
    self.messageSender = messageSender
    self.messageSender.fromWidgetSignal.emit("Widget sends a value.")

The old way seemed simpler to me:

connect and emit in the main window like this:

	self.emit(QtCore.SIGNAL("fromMainWindowSignal"), "Main Window sends a value.")

and in the widget like this:
        self.emit(QtCore.SIGNAL("fromWidgetSignal"), "Widget sends a value.")

No extra class and no sending parameters.  Did I do the new way right and if so, why do I want to? 

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