.property('objectName') always returns empty string

WoR473 · wrote on 17 Jul 2022, 11:41

I'm wanting to iterate over all objects within the rootObject (getting objectName of each child in the process). I have the following code which appears to read some properties back, but for some reason, property objectName always returns an empty string. Also, could someone explain the "hidden" QObjects that print out which are not in the QML.

import os
from pathlib import Path
import sys

from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine
from PySide6.QtCore import QObject


if __name__ == "__main__":
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    engine.load(os.fspath(Path(__file__).resolve().parent / "main.qml"))
    rootObject = engine.rootObjects()[0]

    objList = rootObject.findChildren(QObject, "")

    for object in objList:
        print(object)
        print("objectName: " + object.property('objectName'))
        print("width: " + str(object.property('width')))

    sys.exit(app.exec())

QML:

import QtQuick
import QtQuick.Window
import QtQuick.Controls

Window {
    objectName: "window"
    width: 540
    height: 700
    visible: true
    color: "#ffffff"
    title: qsTr("Calc")

        Button {
            objectName: "button1"
            id: b1
            width: 120
            height: 80
            text: qsTr("7")
            flat: false
            highlighted: false
            font.bold: true
            font.pointSize: 12
        }
}

Console Output:

<PySide6.QtCore.QObject(0x220a0511020) at 0x00000220A0780940>
objectName: 
width: 540.0
<PySide6.QtCore.QObject(0x220a16dcde0) at 0x00000220A0818D40>
objectName: 
width: None
<PySide6.QtCore.QObject(0x220a0519960) at 0x00000220A0818B80>
objectName: 
width: 120.0
<PySide6.QtCore.QObject(0x220a15ddf70) at 0x00000220A0818BC0>
objectName: 
width: None
<PySide6.QtCore.QObject(0x220a15eeb70) at 0x00000220A0818CC0>
objectName: 
width: 120.0
<PySide6.QtCore.QObject(0x2209e682ec0) at 0x00000220A0818C00>
objectName: 
width: 112.0

SGaist · 17 Jul 2022, 13:42

Hi,

Just I wild guess, but I think that you are requesting the objects too early in the process. The QML side is likely not yet fully loaded.

What about using the objectCreated signal ?

WoR473 · S SGaist 17 Jul 2022, 13:18

@SGaist Thank you for the response.

Unfortunately this doesn't appear to be the cause (assuming the changes that i made had the desired effect, which it appears they did to my noob eyes).

# This Python file uses the following encoding: utf-8
import os
from pathlib import Path
import sys
from time import sleep

from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine
from PySide6.QtCore import QObject, QTimer


if __name__ == "__main__":
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    engine.load(os.fspath(Path(__file__).resolve().parent / "main.qml"))
    rootObject = engine.rootObjects()[0]

    objList = rootObject.findChildren(QObject, '')

    def printObjNames():
        for object in objList:
            print(object)
            print("objectName: " + object.property('objectName'))
            print("width: " + str(object.property('width')))

    QTimer().singleShot(3000, printObjNames)
    sys.exit(app.exec())

Console output is identical to first post, with the exception of the 3 second delay before it appears.

WoR473 · wrote on 17 Jul 2022, 14:18

I tried utilizing the objectCreated signal, i'm not sure i've done this right, i can't find any examples of using this signal and i'm not "up" on slots/signals yet. newObj() never runs so if i've set this up right it appears that it never gets done loading?

import os
from pathlib import Path
import sys
from time import sleep

from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine
from PySide6.QtCore import QObject, QTimer


if __name__ == "__main__":
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    engine.load(os.fspath(Path(__file__).resolve().parent / "main.qml"))
    rootObject = engine.rootObjects()[0]

    objList = rootObject.findChildren(QObject, '')

    def printObjNames():
        for object in objList:
            print("objectName: " + object.property('objectName'))
            print("width: " + str(object.property('width')))

    def newObj():
        print("loaded new obj")

    engine.objectCreated.connect(newObj)
    QTimer().singleShot(3000, printObjNames)
    sys.exit(app.exec())

WoR473 · wrote on 17 Jul 2022, 14:37

Disregard my prev post, i must be doing something wrong there. I did find that if i specify the object name in .findChildren, then it returns the object with the objectName, but for some reason if i just try to grab all the children, then iterate through them, that does not work.

import os
from pathlib import Path
import sys
from time import sleep

from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine
from PySide6.QtCore import QObject, QTimer


if __name__ == "__main__":
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    engine.load(os.fspath(Path(__file__).resolve().parent / "main.qml"))
    rootObject = engine.rootObjects()[0]

    objList = rootObject.findChildren(QObject, '')

    for object in objList:
        print(object)
        print("objectName: " + object.property('objectName'))
        print("width: " + str(object.property('width')))

    objList = rootObject.findChildren(QObject, 'button1')

    for object in objList:
        print(object)
        print("objectName: " + object.property('objectName'))
        print("width: " + str(object.property('width')))

    sys.exit(app.exec())

Console Output:

<PySide6.QtCore.QObject(0x1d998384480) at 0x000001D997519180>
objectName: 
width: 540.0
<PySide6.QtCore.QObject(0x1d9983942d0) at 0x000001D997518F40>
objectName: 
width: None
<PySide6.QtCore.QObject(0x1d9982f4240) at 0x000001D997518FC0>
objectName: 
width: 120.0
<PySide6.QtCore.QObject(0x1d9982ec280) at 0x000001D997519000>
objectName: 
width: None
<PySide6.QtCore.QObject(0x1d9983123d0) at 0x000001D997519100>
objectName: 
width: 120.0
<PySide6.QtCore.QObject(0x1d9984ac540) at 0x000001D997519080>
objectName: 
width: 112.0
<PySide6.QtCore.QObject(0x1d9958b2240, name = "button1") at 0x000001D997518F00>
objectName: button1
width: 120.0

WoR473 · wrote on 17 Jul 2022, 15:05

I found that removing the string completely (instead of using an empty string) did the trick. I'm not sure why i thought that would work in the first place, i think it was one of those lets try it and see what happens and i had objects coming back so i assumed i was iterating over everything there.

Instead of:

objList = rootObject.findChildren(QObject, '')

This:

objList = rootObject.findChildren(QObject)

Console Output:

<PySide6.QtCore.QObject(0x1d9374b9e80) at 0x000001D9390F90C0>
objectName: 
width: 540.0
<PySide6.QtCore.QObject(0x1d939f97080) at 0x000001D9390F8EC0>
objectName: 
width: None
<PySide6.QtCore.QObject(0x1d9374eade0, name = "button1") at 0x000001D9390F8F40>
objectName: button1
width: 120.0
<PySide6.QtCore.QObject(0x1d939fda1d0) at 0x000001D9390F8F80>
objectName: 
width: 120.0
<PySide6.QtCore.QObject(0x1d939eee640) at 0x000001D9390F9040>
objectName: 
width: None
<PySide6.QtCore.QObject(0x1d939fda050) at 0x000001D9390F8FC0>
objectName: 
width: 120.0
<PySide6.QtCore.QObject(0x1d9374e9720) at 0x000001D9390F9000>
objectName: 
width: 112.0
<PySide6.QtCore.QObject(0x1d939fbfde0, name = "label") at 0x000001D9390F8F00>
objectName: label
width: 9.0

I assume that by specifying an empty string it is finding components with no objectName set, but what is curious to me still is what are these mystery components?

SGaist · wrote on 17 Jul 2022, 18:54

I knew that empty string was nagging me for a reason...

There are several QObjects that can be created as part of the object tree that supports your application.