How come Featured Image isn't showing up in my Custom Post Type?

Question

I have thumbnail support added with the following in my functions.php

// Add Thumbnail Support
add_theme_support('post-thumbnails');
set_post_thumbnail_size( 140, 140, true );

And I create the custom post type with

// Create Custom Post Type for Work
add_action( 'init', 'create_post_type' );
function create_post_type() {
register_post_type( 'custom_post',
    array(
        'thumbnail',
        'labels' => array(
            'name' => __( 'Custom' ),
            'singular_name' => __( 'Custom' )
        ),
        'public' => true,
        'has_archive' => true,
        'rewrite' => array('slug' => 'custom'),
        'taxonomies' => array('category', 'post_tag')
    )
  );
}

However, when I create a new post in the Custom Post Type, the Featured Image meta box does not show. I have also tried using an array when declaring the custom post type, as follows but that didn't work either

// Add Thumbnail Support
add_theme_support('post-thumbnails', array ('post','work','custom_post'));
set_post_thumbnail_size( 140, 140, true );

What am I missing?

Answer 1

try the register_post_type supports parameter:

'supports' => array( 'thumbnail' )

Answer 2

Add this parameter into your array:

'supports' => array('thumbnail'),

Edit: Milo was faster.

Answer 3

Try this it works for me.....

add_theme_support('post-thumbnails');
add_post_type_support( 'my_product', 'thumbnail' );    
function create_post_type() {
        register_post_type( 'my_product',
            array(
                'labels' => array(
                    'name' => __( 'Products' ),
                    'singular_name' => __( 'Product' )
                ),
                'public' => true,
                'has_archive' => true
            )
        );
    }
    add_action( 'init', 'create_post_type' );