Qt Quick using delegate and call 'parent'

taedooly

ListView {
            id: cowListView
            width: parent.width
            Layout.alignment: Qt.AlignHCenter | Qt.AlignVCenter
            model: _ResourceVec.getSize()
            delegate: ItemDelegate {
                width: parent.width
                anchors.horizontalCenter: parent.horizontalCenter

When i use delegate in list view and then call parent in it, this error occur.

TypeError: Cannot read property 'width' of null
TypeError: Cannot read property 'horizontalCenter' of null

it seems like have problem getting 'parent '.
But somehow my code works perfectly as i intended
I'm ignoring that error but i know why it happens and what is the perfect solution.

i use QT 5.14.2 and used library is

import QtQuick 2.12
import QtQuick.Layouts 1.14
import QtQuick.Controls 2.12

jeremy_k

Instances of the delegate aren't direct children of the view. The implementation looks something like this:

ListView
 |-ListView contentItem
     |-delegate instance 0
     |-delegate instance 1
     | ...
     |-delegate count - 2
     |-delegate count - 1

To have a delegate instance refer to the properties of the ListView, either reference it by id:

delegate: ItemDelegate {
  width: cowListView.width
}

or use the attached properties:

delegate: ItemDelegate {
  width: ListView.view.width # ListView.view == cowListView
}

Using attached properties is advantageous for portability. Renaming cowListView won't break its delegate. On the other hand, the attached properties are only attached to the top level delegate. Descendents of the delegate generally need to explicitly reference the top of the delegate tree in some form.