Whose attribute is the 'index' attribute in the QML example?

[mirro]

ListView {
    id: listView
    model: 10
    delegate: ItemDelegate {
        text: modelData
        highlighted: ListView.isCurrentItem
        onClicked: listView.currentIndex = index
    }
}

[J.Hilk]

@mirro it is automatically added to the delegate of all Components that can have a delegate

ListView, Repeater ....etc

[GrecKo]

That's a context property given by the view when it instantiates the delegate.

Note that this feature is meant to be replaced by required properties in newer code : https://www.qt.io/blog/new-qml-language-features-in-qt-5.15

[mirro]

@J-Hilk Why is the display of ItemDelegate and ListModel used together problematic?
The following two examples show different effects

import QtQuick.Window 2.2
import QtQuick.Controls 2.2

ListModel {
    id:contactModel
    ListElement {
        name: "Bill Smith"
        number: "555 3264"
    }
    ListElement {
        name: "John Brown"
        number: "555 8426"
    }
    ListElement {
        name: "Sam Wise"
        number: "555 0473"
    }
}

Window {
    visible: true
    width: 300
    height: 450
    title: qsTr("Hello World")

    ListView{
        id:listView
        anchors.fill: parent
        model:contactModel
        snapMode: ListView.SnapOneItem
        orientation:ListView.Horizontal
        delegate: ItemDelegate {
                  Rectangle{
                  
                                width: listView.width
                  
                                height: listView.height
                  
                                color: index%2 ? "red":"yellow"
                  
                                Label{
                  
                                    anchors.centerIn: parent
                  
                                    font.pointSize: 100
                  
                                    text: index
                  
                                }
                  
                          }
               }
    }
}

import QtQuick.Window 2.2
import QtQuick.Controls 2.2

Window {
    visible: true
    width: 300
    height: 450
    title: qsTr("Hello World")

    ListView{
        id:listView
        anchors.fill: parent
        model:10
        snapMode: ListView.SnapOneItem
        orientation:ListView.Horizontal
        delegate: Rectangle{
              width: listView.width
              height: listView.height
              color: index%2 ? "red":"yellow"
              Label{
                  anchors.centerIn: parent
                  font.pointSize: 100
                  text: index
              }
        }
    }
}