Codeigniter表单验证，哪个规则触发？

Question

When form_validation->run() returns FALSE, I need to know which rule didn't pass the validation test.
I know I can echo form_error() or validation_errors(), but this needs to be done before a view is loaded. The controller needs to act differently according to which input didn't pass the validation.

Example:

public function index()
{
    $this->load->library('form_validation');

    $this->form_validation->set_rules('username', 'Username', 'required');
    $this->form_validation->set_rules('password', 'Password', 'required');

    if ($this->form_validation->run())
    {
        $this->load->view('something');
    }
    else
    {
        //check which rule didn't pass and act accordingly
    }
}

I tried using empty on form_error('something') from within the if statement but this returns an error as empty doesn't take functions.
Also note, I can't change the error delimiters because they are used elsewhere in the script.

How would I check which rule was triggered without echoing validation_errors()?

Answer 1

To display an error message using a specific field form_error('username')