I need to add a theme-switching logic to a site. Unfortunately, what I've tried already doesn't seem to work as required.

The themes needs to switch based on whether the user is on the blog part of the site (e.g. is_single(), is_category(), get_post_type() == 'post'), versus any other section (e.g. is_shop(), is_page(), etc.)

Unfortunately, having created a plugin to do this, it appears that none of these conditionals are available at the only point I can feasibly hook in: setup_theme.

With the following:

function vnmFunctionality_getTheme() {

    $isBlog = (is_author() || is_category() || is_tag() || is_date() || is_home() || is_single()) && 'post' == get_post_type();

    if ($isBlog) {
        return 'blog-theme';
    } else {
        return 'site-theme';

function vnmFunctionality_conditionalThemeSwitch() {
    if (is_admin()) {

    add_filter('template', 'vnmFunctionality_getTheme');
    add_filter('stylesheet', 'vnmFunctionality_getTheme');

add_action('setup_theme', 'vnmFunctionality_conditionalThemeSwitch', 100);

This works (insofar as there are no errors), but $isBlog will always return false because none of those conditionals are available at setup_theme. If I don't use add_action('setup_theme') and instead move the add_filter lines to the root of the plugin, the conditionals are available, but it causes a host of other issues (for example, the blog-theme seems to try to act like a messed-up quasi-child of site-theme, and fails to load everything that's enqueued in site-theme's functions file).

I also tried looking at the global $wp_query object to see if I could figure out where you are on the site, but even that seems to be empty at setup_theme.

I can't seem to hook in any later than setup_theme for the theme-switching to work properly, but that seems too early to be able to figure out where the user actually is on the site. Is there a way of achieving this?

For reference: The need is based on requirements outside of my influence (read: client). This secondary 'blog-only' theme is fundamentally different from the rest of the site (and was produced by another developer), so unfortunately integrating it into the existing theme isn't feasible.


Assuming that the blog part of the site has a different url-structure (eg www.example.com/blog/this-is-my-blogpost) you can use the PHP $_SERVER variable to determine which page is being called and use that in an expression to make $isBlog true at the appropriate moment.

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