How to add CSS style sheet dynamically in wordpress

Question

When certain conditions are met (e.g. post vs. page or a category is tagged, etc) I would like to load an additional CSS file. This file would, in theory, change link colors. Or perhaps change the background color. Cosmetic changes. My thinking was to add code to functions.php, however, I don't think this is actually adding the CSS page. Even (even though right now there is no conditional, it should always just add this new page).

Help?

 /*
  * register with hook 'wp_print_styles'
  */
  add_action('wp_print_styles', 'add_my_stylesheet');

/*
 * Enqueue style-file, if it exists.
 */

function add_my_stylesheet() {
    $myStyleUrl = WP_THEME_URL . '/newStyle.css';
    $myStyleFile = WP_THEME_URL . '/newStyle.css';
    if ( file_exists($myStyleFile) ) {
        wp_register_style('myStyleSheets', $myStyleUrl);
        wp_enqueue_style( 'myStyleSheets');
    }

}

Thank you

Answer 1

It seems like copy/paste gone wrong - both your variables point to same URL link and so file_exists() fails because it expects local path.

Change $myStyleFile to local path and it should work.

Answer 2

Use WordPress Conditional tags in your functions.php file to register and enqueue on specific pages in your theme: http://codex.wordpress.org/Conditional_Tags

    // script manager template for registering and enqueuing files
    function childtheme_script_manager() {
        // register custom style on your specific page
        // use WordPress conditionals: 
        if (is_page('your-page-slug')) {
            wp_register_style('custom-css', get_stylesheet_directory_uri() . '/custom-style.css');
            wp_enqueue_style ('custom-css-css');
        }
    }
    add_action('wp_enqueue_scripts', 'childtheme_script_manager');