upload featured image from front end using wordpress add media button

Question

I want to submit custom post from frontend. i have made form to make this happened. But i want to upload featured image form add media button of wordpress.

Code is

<?php
/*
Template Name: post submition Template

Description: Use this page template to hide the sidebar. Alternatively
you can simply remove all widgets from your sidebar to hide it on
all pages.
*/
?>

<?php get_header(); ?>
<?php 

// Check if the form was submitted
if( 'POST' == $_SERVER['REQUEST_METHOD'] && !empty( $_POST['action'] )) {

// Do some minor form validation to make sure there is content
if (isset ($_POST['title'])) { 
    $title =  $_POST['title']; 
} else { 
    echo 'Please enter a title';
}
if (isset ($_POST['description'])) { 
    $description = $_POST['description']; 
} else { 
    echo 'Please enter the content'; 
}

// Add the content of the form to $post as an array
$post = array(
    'post_title'    => $title,
    'post_content'  => $description,
    'post_category' => $_POST['cat'],  // Usable for custom taxonomies too
    'post_status'   => 'draft',         // Choose: publish, preview, future, etc.
    'post_type'     => 'contast'  // Use a custom post type if you want to
);
echo $pid = wp_insert_post($post);  // Pass  the value of $post to WordPress the insert function

    if ($_FILES) {
array_reverse($_FILES);
$i = 0;//this will count the posts
foreach ($_FILES as $file => $array) {
    if ($i == 0) $set_feature = 1; //if $i ==0 then we are dealing with the first post
    else $set_feature = 0; //if $i!=0 we are not dealing with the first post
    $newupload = insert_attachment($file,$pid, $set_feature);
    echo $i++; //count posts
    }
    } 


//attachment helper function   

            // http://codex.wordpress.org/Function_Reference/wp_insert_post
    //wp_redirect( '/submit-2/' ); // redirect to home page after submit

} // end IF
// Do the wp_insert_post action to insert it
?>

<form action="" method="post" enctype="multipart/form-data">
<p><label for="title">Titolo</label><br />
        <input type="text" id="title" value="" tabindex="1" size="20" name="title" />
        </p>
        <p><label for="description">Testo</label><br />
        <textarea id="description" tabindex="3" name="description" cols="50" rows="6"></textarea>
        </p>

<label for="file">Filename:</label>
<input type="file" name="file" id="file"><br>
<p align="right"><input type="submit" value="Invia" tabindex="6" id="submit" name="submit" /></p>

        <input type="hidden" name="post_type" id="post_type" value="domande" />
    <input type="hidden" name="action" value="post" />
    <?php wp_nonce_field( 'new-post' ); ?>
</form>

<?php get_footer(); ?>

and function is

function insert_attachment($file_handler,$post_id,$setthumb='false') {
if ($_FILES[$file_handler]['error'] !== UPLOAD_ERR_OK){ return __return_false(); 
} 
require_once(ABSPATH . "wp-admin" . '/includes/image.php');
require_once(ABSPATH . "wp-admin" . '/includes/file.php');
require_once(ABSPATH . "wp-admin" . '/includes/media.php');

echo $attach_id = media_handle_upload( $file_handler, $post_id );
//set post thumbnail if setthumb is 1
if ($setthumb == 1) update_post_meta($post_id,'_thumbnail_id',$attach_id);
return $attach_id;
    }

Answer 1

add below code after echo $attach_id....

set_post_thumbnail( $post_id , $attach_id);