Binding with Listview height are not correctly calculated

 ListView {
        id: listview
        //It works with those 2 lines instead of anchors.fill: parent
        //        width: 640
        //        height: 351
        anchors.fill: parent
        property real heightRatio: 0.20
        property int delegateHeight: heightRatio * height
....
        preferredHighlightBegin: (height-delegateHeight)/2
        preferredHighlightEnd: (height+delegateHeight)/2
         // It works if delegateHeight is not used
        //preferredHighlightBegin: (height-(height*heightRatio))/2
        //preferredHighlightEnd: (height+(height*heightRatio))/2
..
}