Get item count in listview itemView yii2

Stackoverflow

How do I get the itemView count. I want to do something on every third item in the ListView.

echo ListView::widget([
    'dataProvider' => $modelDataProvider,
    'itemView'     => '_item_view',
    'viewParams'   => [
        'count' => $itemcount // How to get this variable?
    ],
])

// _item_view.php

if($count % 3 == 0) {
    // this item is the third in a row, do something special
}

Any help is appreciated!