@{
	ViewData["Title"] = "Create";
}
<div class="text-center">
	<h2 class="display-4">Создание заказа</h2>
</div>
<form method="post">
	<div class="row">
		<div class="col-4">Пицца:</div>
		<div class="col-8">
			<select id="pizza" name="pizza" class="form-control" asp-items="@(new SelectList(@ViewBag.Pizzas,"Id", "PizzaName"))"></select>
		</div>
	</div>
	<div class="row">
		<div class="col-4">Количество:</div>
		<div class="col-8"><input type="text" name="count" id="count" /></div>
	</div>
	<div class="row">
		<div class="col-4">Сумма:</div>
		<div class="col-8"><input type="text" id="sum" name="sum" readonly /></div>
	</div>
	<div class="row">
		<div class="col-8"></div>
		<div class="col-4"><input type="submit" value="Создать" class="btn btn-primary" /></div>
	</div>
</form>

<script>
	$('#pizza').on('change', function () {
		check();
	});
	$('#count').on('change', function () {
		check();
	});

	function check() {
		var count = $('#count').val();
		var pizza = $('#pizza').val();
		if (count && pizza) {
			$.ajax({
				method: "POST",
				url: "/Home/Calc",
				data: { count: count, pizza: pizza },
				success: function (result) {
					$("#sum").val(result);
				}
			});
		};
	}
</script>