QObject::findChild() returns None without obvious reason - qt

Question

I'm new to Qt Quck and Qt5/PyQt, and now I've faced a strange problem. I'm trying to find an object with objectName "test" in the below QML definition like this:
self.rootObject().findChild(QObject, "test")
But the call returns None. However, if I move the objectName: "test" property to the parent Tab element, then it's found successfully. It's only not found whem inside the child Item. Similarly, addChannel, modifyChannel and removeChannel objects are also not found by findChild().
import QtQuick 2.0
import QtQuick.Layouts 1.1
import QtQuick.Controls 1.1
import "TouchStyles"
Item {
ListModel { }
TouchButtonFlatStyle { id: touchButtonFlat }
TouchTabViewStyle { id: touchTabView }
Rectangle {
width: 480
height: 230
TabView {
currentIndex: 0
tabPosition: 1
anchors.fill: parent
style: touchTabView
Tab {
title: "Play"
Item {
anchors.fill: parent
PianoKeyboard { anchors.centerIn: parent }
}
}
Tab {
title: "Channels"
Item {
objectName: "test"
ListView {
anchors.fill: parent
model: listModel
delegate: Channel {}
}
BorderImage {
border.bottom: 8
anchors.bottom: parent.bottom
source: "images/toolbar.png"
width: parent.width
height: 50
RowLayout {
anchors.verticalCenter: parent.verticalCenter
anchors.horizontalCenter: parent.horizontalCenter
Button { text: "Add"; objectName: "addChannel" }
Button { text: "Modify"; objectName: "modifyChannel" }
Button { text: "Remove"; objectName: "removeChannel" }
}
}
}
}
}
}
}
What am I doing wrong? The Qt documentation says that the search is performed recursively. Why doesn't it traverse the entire object tree?

Answer 1

The problem is related to the fact that tabs are "instantiated" only on demand. The first tab is always instantiated, so if you put the objectName there it will be found.
It will be found in the second tab only if you instantiate the second tab (select it). Similarly, using findChild on the TabView probably instantiates each tab (since it looking for them), so after that a findChild works even if second tab was not selected.
Conclusion: instantiate all tabs first (doing a findChild on the TabView is one way but may be a hack), then do the findChild for the item.