无法从PHP中获取所选选项

I want to get a selected option from php code below. I keep facing with an error I don't know why I can't get the value.

<html>
    <head>
    </head>
    <body>
        <label>Please select a make below</label> <p></p>
    </body>
</html>

<?php
    include("cars.php");

    if (!class_exists("Cars"))
        echo"<p>The Cars class is not available!</p>";
    else
    {
        $cars = new Cars();

        getList($cars);

            echo $_POST["makesList"]; // I thought I could get the selected with this code but it displays the following error "Undefined index: makesList" 

    }

    function getList($cars)
    {
        $makes = $cars->getMakes();

        $makes=array_unique($makes);

        echo '<form name="makesForm" id="makesForm" method="POST" action="showInventory.php">';
        echo '<select name="makesList" id="makesList">';

        foreach($makes as $make)
            echo '<option value='.$make.'>'.$make.'</option>';
        echo '</select>';
        echo '</form>';



    }
?>

Is there other ways to get the selected value?? FYI, I have a class in Cars.php. I don't think you need to care about that. It displays the list by getList() function well.

PLease try this code instead and do advise if it works.

<?php
    include("cars.php");
    if (!class_exists("Cars"))
        echo"<p>The Cars class is not available!</p>";
    else{
            $cars = new Cars();
            getList($cars);
                echo $_POST["makesList"]; // I thought I could get the selected with this code but it displays the following error "Undefined index: makesList"
            }

    function getList($cars){
        $makes = $cars->getMakes();
        $makes=array_unique($makes);
        echo '<form name="makesForm" id="makesForm" method="POST" action="showInventory.php">';
        echo '<select name="makesList" id="makesList">';
        foreach($makes as $make)
            echo '<option value='.$make.'>'.$make.'</option>';
            echo '</select>';
            echo '</form>';
    }
?>