I'm using apply_filters to bridge the gap between plugins but am struggling with the arguments. There is one argument, an array, there are several implementations of add_filter to match apply_filters and each of them pass down the original array and add to it.

Seems that you can pass several arguments from apply_filter but add_filter can only return one argument, is this correct or how do you handle multiple arguments between add_filter calls?

I need to pass a second argument of an account ID, but it seems that by priority only the first add_filter gets to work with that argument. I plan to wrap up both arguments into a single array and pass that, so an array with an array as its first value and a user ID as its second argument.

Edited to add example

$error = apply_filters('check_for_more_errors', $userid, $error);

add_filter('check_for_more_errors', 'error_check_1', 1, 2);

function error_check($userid, $error){
    $error[] = get_user_meta($userid, 'Plugin 1 user error', true);
    return $error;
}

add_filter('check_for_more_errors', 'error_check_2', 2, 2);

// $userid below is actually $error returned from error_check_1 
function error_check_2($userid, $error){
    $error[] = get_user_meta($userid, 'Plugin 2 user error', true);
    return $error;
}

The above does not work as I expect or need. The filters seem to daisy chain with one the returning argument of the first one being passed as the argument to the next one.

I want both to get the $id variable and for the $error variable to be augmented as in the example.

  • Could you post your code to clarify your question a bit? – Andy Macaulay-Brook Jul 24 '16 at 14:38
  • Edited to add an example. – Peter Bushnell Jul 24 '16 at 18:11
  • Filters do daisy chain as you put it. They are designed that way. – Andy Macaulay-Brook Jul 24 '16 at 18:18
  • 1st arg needs to be the value to be filtered: $error = apply_filters('check_for_more_errors', $error, $userid);, so also fix error_check_* params order. – Samuel Elh Jul 24 '16 at 20:33
  • 1
    @SamuelElh Could you convert your comment to an answer to tidy up? Ta. – Andy Macaulay-Brook Jul 25 '16 at 13:21
up vote 2 down vote accepted

apply_filters requires you to pass the value to be filtered in the 2nd parameter of this function (after the hook tag name)

$error = apply_filters('check_for_more_errors', $error, $userid);

add_filter('check_for_more_errors', 'error_check_1', 1, 2);

function error_check($error, $userid){
    $error[] = get_user_meta($userid, 'Plugin 1 user error', true);
    return $error;
}

add_filter('check_for_more_errors', 'error_check_2', 2, 2);

function error_check_2($error, $userid){
    $error[] = get_user_meta($userid, 'Plugin 2 user error', true);
    return $error;
}

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