如何从onStart（）方法访问请求数据？

Question

I have created page with form in OctoberCMS with two functions onStart() and onSave():

title = "my page"
url = "/blog/new-post"
layout = "octaskin"
is_hidden = 0

[survey]
==
<?php
function onStart()
{
    $this['title'] = post('title');
    var_dump(post());exit; // Always empty!!!
}

function onSave()
{
    var_dump(post());exit; // With data
}

?>
==
{{
    form_open({
        files: true,
        validate: true,
        flash: true,
        request: "onSave"
    })
}}

    <input name="title" type="text" value="{{ title }}">

{{ form_close() }}

I want reinit data in field "title" in case of validation fails. But in onStart() request's data is always empty. How to access request's data from onStart()?