magento 2 accessing foreach variable outside loop

Question

Hi I have got the product collection here but am trying to push $sku value in $item, but seems like its not working, anything wrong am doing, please help

$items = array(); // trying to push sku data in this array
foreach($productCollection as $productCust){
 $sku = $productCust->getSku();// this is working fine
 array_push($items, $productCust->getSku());
}

Update

$items = [];
$productCollection = $this->collectionFactory->create();
$Test = $productCollection->getItems();
foreach($Test as $productCust){
 $sku = $productCust->getSku();// this is working fine
 $items[] = $sku;
}

Answer 1

$items = [];
$products = $productCollection->getItems();
foreach($products as $product){
    $sku = $product->getSku();
    $items[] =  $sku;
}

Answer 2

$items = [];
$productCollection = $this->collectionFactory->create();
$products = $productCollection->getItems();
foreach($products as $product){
 $sku = $product->getSku();
 $items[] = $sku;
}