framework/widgets/ListView.php
protected function renderBeforeItem($model, $key, $index)
    {
        if ($this->beforeItem instanceof Closure) {
            return call_user_func($this->beforeItem, $model, $key, $index, $this);
        }

        return null;
    }
protected function renderBeforeItem($model, $key, $index)
    {
        if ($this->beforeItem instanceof Closure) {
            return call_user_func($this->beforeItem, $model, $key, $index, $this);
        }

        return null;
    }
Calls [[beforeItem]] closure, returns execution result.
If [[beforeItem]] is not a closure, `null` will be returned.

@param mixed $model the data model to be rendered
@param mixed $key the key value associated with the data model
@param int $index the zero-based index of the data model in the model array returned by [[dataProvider]].
@return string|null [[beforeItem]] call result or `null` when [[beforeItem]] is not a closure
@see beforeItem
@since 2.0.11