Dynamically update line item in Commerce 2

Question

I'm currently trying to adjust the line items in a particular cart/order after an event is triggered.

I've got:

use craft\commerce\Plugin as CommercePlugin;

$this->requirePostRequest();
$request = Craft::$app->getRequest();

$cart = CommercePlugin::getInstance()->getCarts()->getCart(true);

$lineItem = CommercePlugin::getInstance()->getLineItems()->getLineItemById($cart->lineItems[0]->id);

$lineItem->price = 100.0000;
$lineItem->salePrice = 100.0000;
$lineItem->qty = 1;
$lineItem->note = '';

$cart->addLineItem($lineItem);

$cart->email = $request->getParam('orderEmail');

if (!Craft::$app->getElements()->saveElement($cart)) {
   return false;
}

But this seems to not do anything, except update $lineItem and not update the line item when the cart is then saved.

Answer 1

Turns out I just replace:

$cart->addLineItem($lineItem);

With:

CommercePlugin::getInstance()->getLineItems()->saveLineItem($lineItem, false);