Add field to user register form

I am adding a field in user register form.

add_action('register_form', array($this, 'add_field_to_register_form'));

This works fine. However I am doing this in 3 plugins, so when the 3 plugins are activated the same field appears 3 times on the register form. I need the field which is the same in three plugins to be displayed just once. If it is displayed by one of the 3 plugins the other 2 plugins must not display it. I tried using this

if   (false === has_action( 'register_form', 'add_field_to_register_form' )) {
add_action('register_form', array($this, 'add_field_to_register_form'));
}

and this

if   (false === has_action( 'register_form', array($this, 'add_field_to_register_form' ))) {
add_action('register_form', array($this, 'add_field_to_register_form'));
}

and this

if   (false === has_action( 'register_form', array(MyClassName::class, 'add_field_to_register_form' ))) {
add_action('register_form', array($this, 'add_field_to_register_form'));
}

but they don’t work. It works like this

if   (false === has_action( 'register_form')) {
add_action('register_form', array($this, 'add_field_to_register_form'));
}

but this does not check the function name so it will work for any other action added to the register form.

Can you please assist? Thanks.

• This topic was modified 5 years, 6 months ago by panicoschr10.