Add custom columns to admin property list

gistfile1.txt

add_filter( 'manage_edit-property_columns', 'lee_edit_columns' );
function lee_edit_columns( $existing_columns ) {

    if ( empty( $existing_columns ) && ! is_array( $existing_columns ) ) {
        $existing_columns = array();
    }

    $columns['reference_number'] = __( 'Reference', 'propertyhive' );

    return array_merge( $columns, $existing_columns );
}

add_action( 'manage_property_posts_custom_column', 'lee_custom_columns', 2 );
function lee_custom_columns( $column ) {
    global $post, $propertyhive, $the_property;

    if ( empty( $the_property ) || $the_property->ID != $post->ID ) 
    {
        $the_property = new PH_Property( $post->ID );
    }

    switch ( $column ) {
        case 'reference_number' :
        {
            echo $the_property->reference_number;
            break;
        }
    }
}