GNURadio: Translate variable change events to Qt Main Thread

qtvarupdate_update_int.block.yml

id: qt_variable_update
label: Qt Variable Update
flags: [ python ]

parameters:
-   id: value
    label: Input Variable
    dtype: int
-   id: target
    label: Output Variable
    dtype: string

templates:
  imports: from gnuradio import qtvarupdate
  make: qtvarupdate.update_int(${ 'self.set_' + context.get('target')() })
  callbacks:
    - set_value(${value})

file_format: 1

update_int.py

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

from gnuradio import gr
from PyQt5 import QtCore

class update_int(gr.sync_block):
    """
    docstring for block update_int
    """
    class QtToMainThread(QtCore.QObject):
        valueChanged = QtCore.pyqtSignal(int)

        def __init__(self, cb):
            QtCore.QObject.__init__(self)
            self.valueChanged.connect(self.onValueChanged)
            self.cb = cb
        
        def set_value(self, value):
            self.valueChanged.emit(value)

        @QtCore.pyqtSlot(int)
        def onValueChanged(self, value):
            self.cb(value)

    def __init__(self, callback):
        gr.basic_block.__init__(self,
            name="update_int",
            in_sig=[],
            out_sig=[])
        self.toMainThread = update_int.QtToMainThread(callback)

    def set_value(self, value):
        self.toMainThread.set_value(int(value))