How can I get a value of html custom view in a controller?

[jamstv]

Hi, I'm using SugarCRM 5.2.0k.

I made a custom html view page.
The problem is I don't know how to get the value in a controller.

here is basically what I did.
<custom/modules/mymodule/views/view.listdetail.php>

 class mymoduleViewListDetail extends ViewListDetail{
    function display(){
        $html = '';
        $html .= '<table>';
        ......
        $html .= '<input type=\'text\' name=\'due_date\' id=\'due_date\'>';
        ......
        $html .= '<button type=\'button\' class=\'button\' title=\'update\' onClick=\'document.location.href="index.php?action=update&module=mymodule";\'>Update</button>';
        ......
        $html .= '</table>';
        echo $html;
    }
} 
  

And in the controller below, how can I get the value of the due_date?
<custom/modules/mymodule/controller.php>

 class mymoduleController extends SugarController{
    function action_update(){
        how can I get the due_date value here?
    } 
  

I'd appreciate any help.
Thank you very much in advance.