// SubItem.qml
import QtQuick 2.15

Item {
    Text {
        anchors.top: parent.top
        text: "SubItem"

        onParentChanged: console.log(this, "has a new parent:", parent)
        Component.onCompleted:   console.log("Hello Text!\t", this)
        Component.onDestruction: console.log("G'bye Text!\t", this)
    }

    Component.onCompleted:   console.log("Hello Item!\t", this)
    Component.onDestruction: console.log("G'bye Item!\t", this)
}

// main.qml
import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15

Window {
    id: root
    width: 640
    height: 480
    visible: true

    property Component comp: SubItem{}

    Column{
        Button {
            text: "Reload"
            onClicked: {
                loader.active = false
                loader.active = true
            }
        }

        Loader {
            id: loader
            sourceComponent: Item {
                id: loadedItem
                width: 50
                height: 50
                Component.onCompleted: root.comp.createObject(loadedItem)
            }
        }
    }
}