Not able to change wp_title using add_filter

Question

I have a custom page where I try to change the page title.
The function executes, but the title is not changed. This is the code I'm using:

  add_filter('wp_title', set_page_title($brand));

  function set_page_title($brand) { 
    $title = 'Designer '.$brand['name'].' - '.get_bloginfo('name');
    //Here I can echo the result and see that it's actually triggered
    return $title;  
  } 

So why is this not working? Am I using add_filter wrong?

Answer 1

You cannot pass an array to set_page_title, the filters callback accept only the original title as input parameter.

If you want your function work this way, define the $brand array outside the function and make it global

  add_filter('wp_title', set_page_title);

  $brand = array('name'=>'Brand Name');

  function set_page_title($orig_title) { 
    global $brand;
    $title = 'Designer '.$brand['name'].' - '.get_bloginfo('name');
    //Here I can echo the result and see that it's actually triggered
    return $title;  
  }

Answer 2

What is happening in both examples of code is that add_filter is not calling a function to accept a return as the new title. The function add_filter expects at least two parameters, the first being a string that contains the 'tag' or name of the filter you would like to use, and the second is mixed. In the case of using a defined function you should use the function name as a string, it can also accept an array for a callback within a namespace, and an anonymous function.

In the case of:

add_filter('wp_title', set_page_title('test'));

The inner most function will be evaluated first, passing its return results to the next outer function.

So...

add_filter('wp_title', set_page_title(other_function(function() {return "real_filter";})));

Would pass the string 'real_filter' to add_filter assuming that all functions between the two pass their input parameters as their return value.

I believe what you would want would be something along the lines of:

function my_title_filter($old_title, $sep, $seplocation) {
    // Add some code to determine if/what you want to change your title to.

    global $brand;

    $title = "Designer " . $brand['name'] . " $sep " . get_bloginfo('name');

    return $title;
}

add_filter('wp_title', 'my_title_filter', 10, 3); // 10 is the priority,
    // and 3 is the number of arguments the function accepts.
    // wp_title can pass 3.

An additional caveat... The filter must be initialized before apply_filters is called. And best practice is to have your function defined prior to calling add_filter.

Answer 3

Steve hit it on the nose. This article has a complete example if you're trying to do this for a WP theme.