How to use signals and slots in Slicer 3d?

Support
1

I am familiar with pyqt. I want to use signals and slots mechanism in my slicer python script. For some reason when I am connecting the signal to the slot, slicer is exiting abnormally.
Screenshot from 2020-10-13 19-57-03
How to use signals and slots in slicer pythonqt?

2

A previous post of mine mentioned some about basics of using Qt signals and slots with python.

Essentially the syntax is something like {object}.{signal_name}.connect({slot_name}).

So something that is based on QProgressBar will have these signals such as valueChanged. Therefore

def printMyNewValue(value):
  print("The progress bar value is now: {}".format(value))

import qt
progress_bar = qt.QProgressBar()
progress_bar.setMaximum(10)
progress_bar.valueChanged.connect(printMyNewValue)
progress_bar.setValue(4)  # will then print "The progress bar value is now: 4"
3

I want to create a new signal and then connect it to a slot. I don’t want to use the pre-defined signals of widgets.

4

Screenshot from 2020-10-13 19-57-03

When I am executing the above code slicer is exiting abnormally. How can I create a new signal in slicer that works fine?

5

This example works for me:

class C(qt.QObject):
    received = qt.Signal(object)
    def __init__(self):
        super(C, self).__init__(None)
    def process(self, msg):
        self.received.emit(msg)

class D(qt.QObject):
    def __init__(self, sender):
        super(D, self).__init__(None)
        sender.received.connect(self.process)
    def process(self, msg):
        print("Processed this: "+repr(msg))

c = C()
d = D(c)
m = {'h': {'t': 's'}, 'c': {'e': 'i'}}

c.process(m)

(taken from these discussions: Custom Signal/Slots with PythonQt - #6 by ihnorton and PythonQt / Discussion / Help: Segmentation fault after emiting a signal)

However, normally there is no need to create Qt-based Python classes and define new signals and slots, as you can communicate via MRML nodes and VTK event observations:

What is your use case? What would you like to achieve with the custom signals/slots?

6

I want to change the progress of a progressbar from another thread.
i want to create a signal(int) and connect it to progressBar.setValue(int).
But when I am connecting it is exiting…