QT QML Accessing Attached Property From Another QML Object - qt

Question

main.qml:
import QtQuick 2.11
import QtQuick.Controls 2.2
import QtQuick.Layouts 1.3
ApplicationWindow {
id: window
x: 200
y: 200
visible: true
Component {
id: firstViewComponent
FirstView {
id: firstView
}
}
StackView {
id: stackView
anchors.fill: parent
Component.onCompleted: push(firstViewComponent)
}
Timer {
interval: 1000
running: true
onTriggered: stackView.pop()
}
}
FirstView.qml:
Rectangle {
id: view
StackView.onDeactivating: console.log('view: view is deactivating')
ListModel {
id: aModel
ListElement {
name: 'Element 0'
}
ListElement {
name: 'Element 1'
}
}
ListView {
id: listView
model: aModel
delegate: Rectangle {
id: listViewDelegate
Connections {
target: view.StackView // <---- DOESN'T WORK
onDeactivating: console.log('delegate ' + index + ': needs to do some housekeeping now')
}
}
}
}
I have a view that is instantiated by a StackView in main.qml. The StackView attaches a signal StackView.onDeactivating to the view. Is there any way to attach to the signal from an object other than the one the signal is attached to? I need to do some cleanup in listViewDelegate when the view is popped.
I could have view emit its own signal, and have the delegate respond to that signal. But what I'm wondering is if there is a way to connect to the attached signal: StackView.onDeactivating from a different object (listViewDelegate).

Answer 1

Yes and no. The Qt documentation partially addresses this: A Note About Accessing Attached Properties and Signal Handlers
It is not possible to directly access the property from a child. Attached properties need to be explicitly read by the class providing them. For your example, the parent class (StackView) simply searches for all attached properties it does provide in the child item (FirstView) as soon as it gets added, and handles all found properties/signals etc. by connecting them internally to whatever logic provides them.
However, nothing prevents you from gettings the attached property from the parent item, as long as you refer to it by id:
sampleProp: view.StackView.someProperty
The thing is: This indirect access only works this way for properties and nor for signals, as you can't simply refer to the attached object via view.StackView - so sadly, you are stuck with forwarding the signal to the child elements indirectly by creating a second signal in the root item and emitting it when the attached signal gets emitted.