Hide admin toolbar based on a query string

Question

As far as I know the showing and hiding of the admin toolbar on the front-end is a global setting, which applies to any page containing wp_footer().

I want to have more specific control over the visibility admin bar—specifically, to be able to hide it based on a URL query string, such as (e.g., ?hidetoolbar at the end of a URL).

I know that I can hide the toolbar from a specific template file by adding this to the top:

     add_filter('show_admin_bar', '__return_false');

What hook would I use to apply the filter conditionally in functions.php?

Answer 1

You should be able to just add the filter inside of a conditional:

<?php if ($_GET['hidetoolbar']) 
{
    add_filter('show_admin_bar', '__return_false');
}
?>

or, since conditionally adding action handlers and filters is sometimes frowned upon, you could add your own function as a filter and then put your conditional inside that:

<?php 
function my_manage_toolbar()
{
    if ($_GET['hidetoolbar']) 
    {
        return false;
    }
    return true;
}
add_filter('show_admin_bar', 'my_manage_toolbar');
?>

Answer 2

You can try this in your functions.php file :

if (isset($_GET['hidetoolbar'])) {
    add_filter('show_admin_bar', '__return_false');
}