Order by modified date working in POSTS but not PAGES

Question

I found the following code at bytefreaks.net. It adds a sort-able column to edit.php, but the column appears only on Posts and not on Pages (...?post_type=page)

bytefreaks suggested putting it in functions.php but I wanted to avoid update problems so I installed the "My Custom Functions" plugin and put the code there.

I don't know WordPress well enough to fully understand each function. Can anyone tell me what I need to do to make this code work for Pages as well as Posts?

// Register the column
function post_modified_column_register( $columns ) {
    $columns['post_modified'] = __( 'Modified', 'mytextdomain' );
    return $columns;
}
add_filter( 'manage_edit-post_columns', 'post_modified_column_register' );

// Display the column content
function post_modified_column_display( $column_name, $post_id ) {
    if ( 'post_modified' != $column_name ){
        return;
    }
    $post_modified = get_post_field('post_modified', $post_id);
    if ( !$post_modified ){
        $post_modified = '' . __( 'undefined', 'mytextdomain' ) . '';
    }
    echo $post_modified;
}
add_action( 'manage_posts_custom_column', 'post_modified_column_display', 10, 2 );

// Register the column as sortable
function post_modified_column_register_sortable( $columns ) {
    $columns['post_modified'] = 'post_modified';
    return $columns;
}
add_filter( 'manage_edit-post_sortable_columns', 'post_modified_column_register_sortable' );

Answer 1

Check the documentation for the Plugin API/Filter Reference

Looks like you need to duplicate your actions and filters for manage_pages_custom_columns/manage_edit-page_columns etc etc. Fair warning: I've not vetted this.

See below

https://codex.wordpress.org/Plugin_API/Filter_Reference/manage_edit-post_type_columns https://codex.wordpress.org/Plugin_API/Action_Reference/manage_pages_custom_column

Here's the resulting code that works:

// Custom Functions to add SORT BY MODIFIED to post and page editor.
// POSTS
// Register the column
function post_modified_column_register( $columns ) {
    $columns['post_modified'] = __( 'Modified', 'mytextdomain' );
    return $columns;
}
add_filter( 'manage_edit-post_columns', 'post_modified_column_register' );

// Display the column content
function post_modified_column_display( $column_name, $post_id ) {
    if ( 'post_modified' != $column_name ){
        return;
    }
    $post_modified = get_post_field('post_modified', $post_id);
    if ( !$post_modified ){
        $post_modified = '' . __( 'undefined', 'mytextdomain' ) . '';
    }
    echo $post_modified;
}
add_action( 'manage_posts_custom_column', 'post_modified_column_display', 10, 2 );

// Register the column as sortable
function post_modified_column_register_sortable( $columns ) {
    $columns['post_modified'] = 'post_modified';
    return $columns;
}
add_filter( 'manage_edit-post_sortable_columns', 'post_modified_column_register_sortable' );
//PAGES
// Register the column
function page_modified_column_register( $columns ) {
    $columns['page_modified'] = __( 'Modified', 'mytextdomain' );
    return $columns;
}
add_filter( 'manage_edit-page_columns', 'page_modified_column_register' );

// Display the column content
function page_modified_column_display( $column_name, $page_id ) {
    if ( 'page_modified' != $column_name ){
        return;
    }
    $page_modified = get_post_field('post_modified', $page_id);
    if ( !$page_modified ){
        $page_modified = '' . __( 'undefined', 'mytextdomain' ) . '';
    }
    echo $page_modified;
}
add_action( 'manage_pages_custom_column', 'page_modified_column_display', 10, 2 );

// Register the column as sortable
function page_modified_column_register_sortable( $columns ) {
    $columns['page_modified'] = 'page_modified';
    return $columns;
}
add_filter( 'manage_edit-page_sortable_columns', 'page_modified_column_register_sortable' );

// end SORT BY MODIFIED