Validation based on another field's value

[eluser]CroNiX[/eluser]
I haven't set up my rules using a multidimensional array like you are, but I usually do something like:

Code:

//the field with the checkbox
$check1 = $this->input->post('field_with_checkbox');
$rules = '';
if($check1 !== FALSE && $check1 == '1')
{
  //if the checkbox was checked, add a required field to the rules for the other field
  $rules .= 'required|';
}
//append regular rules for the field
$rules .= 'trim|xss_clean';
//apply rules to the textbox field, "Explain"
$this->form_validation->set_rules('field', 'label', $rules);

That might not be exactly right, I can't check right now.