Use add_filter on concatenated string variable

Question

I have a HTML table that I am concatenating like this:

$admin_table_output .= "Item Description: </td><td>";
$admin_table_output .= "<input type='text' name='name' value='$name'></td><td> (Optional)</td></tr><tr><td colspan='4'>";

$admin_table_output is echo'ed out at the end. That works just fine.

My problem is that I want to use apply_filters to modify the variable $admin_table_output like so:

$admin_table_output .= "Item Description: </td><td>";

apply_filters('tabs_page_static_value',$admin_table_output);

$admin_table_output .= "<input type='text' name='name' value='$name'></td><td> (Optional)</td></tr><tr><td colspan='4'>";

Using a hook like this:

function tabs_page_static_value_filter($admin_table_output) {

     $admin_table_output .= 'testing';

     return $admin_table_output;

}
add_filter('tabs_page_static_value','tabs_page_static_value_filter',10,1);

However this does not work. I've also tried using do_action instead, I've tried to echo the variable instead of return it and also not concatenating inside the hook.

I'm thinking I might need to do some kind of a variable variable thing to solve this problem. Any ideas?

Answer 1

As @Sally mention in the comment. if you want to let others to extend the HTML code. you should also append the new HTML they returning in the filter.

Try code below

$admin_table_output .= "Item Description: </td><td>";

$admin_table_output = apply_filters('tabs_page_static_value',$admin_table_output);

$admin_table_output .= "<input type='text' name='name' value='$name'></td><td> (Optional)</td></tr><tr><td colspan='4'>";