'Connections' object does not listen to changes in target?

patrickkidd

Am I correct in assuming that a Connections object does not re-connect to the new value of target when target changes? Surely this is a bug?

For example, the following code fails:

test_qml.qml

import QtQuick 2.15
import com.tester.stuff 1.0

Item {
    id: root

    property var mine: Mine {}
    property var theirs: null

    onMineChanged: print('onMineChanged:', mine)
    
    Connections {
        target: mine
        function onYoursChanged() {
            print('onYoursChanged', mine.yours)
        }
    }

    Connections {

        // this connects to the first value of &.yours,
        // but does not switch to new values of &.yours,
        // even when `mine.yoursChanged` is emitted.
        target: mine.yours 

        function onTheirsChanged() { // never called
            print('onTheirsChanged', theirs)
            root.theirs = mine.yours.theirs
        }
    }
}

test_qml.py

from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtQml import *
from PyQt5.QtQuick import *
from PyQt5.QtQuickWidgets import *


class Yours(QObject):
    
    theirsChanged = pyqtSignal(int)

    def __init__(self, parent, theirs):
        super().__init__(parent)
        self._theirs = theirs

    @pyqtProperty(int, notify=theirsChanged)
    def theirs(self):
        return self._theirs


class Mine(QObject):

    yoursChanged = pyqtSignal(QVariant)

    def __init__(self, parent=None):
        super().__init__(parent)
        self._yours = Yours(self, -1)

    @pyqtProperty(QVariant, notify=yoursChanged)
    def yours(self):
        return self._yours

    def setYours(self, x):
        self._yours = Yours(self, x)
        self.yoursChanged.emit(self._yours)


qmlRegisterType(Mine, "com.tester.stuff", 1, 0, "Mine")

app = QApplication([])
engine = QQmlEngine()
searchView = QQuickWidget()
searchView.setSource(QUrl.fromLocalFile("test_qml.qml"))
mine = searchView.rootObject().property('mine')

mine.setYours(1)
assert searchView.rootObject().property('theirs') == mine.yours.theirs

mine2 = Mine()
mine2.setYours(2)
searchView.rootObject().setProperty('mine', mine2) # `Connections` doesn't update to the new value of mine.yours
assert searchView.rootObject().property('theirs') == mine2.yours.theirs

patrickkidd

Just looping back here to see if anyone has any ideas. Maybe a pattern to avoid this behavior? It would be great to have some kind of global context property that can be used in Connection object and who's value can change.

dheerendra

This should work. It is ok to change the larget. It works in c++. I have not tried with Python.