How to add 'not equal' condition in form #states

Question

In my form, there are 3 selection list A, B and C.

I wanna show or hide C based on values of A and B selected. C should be shown if A's value = 'all and B's value != 'all'

How to set the #state condition in this case?

 $form['C'] = array(
        '#type' => 'select',
        '#title' => t('C'),
        '#states' => array(
            'visible' => array(
                ':input[name="A"]' => array('value' => 'all'),
                ':input[name="B"]' => array('value' => 'all') //???how to set !='all' here?
            )
        )
)

Answer 1

This code should work:

':input[name="B"]' => array('!value' => 'all')

Answer 2

Although I don't think you can make negative condition with states in D7, you can make C invisible when B value equal all.

$form['C'] = array(
    ...
    '#states' => array(
       'visible' => array(
          ':input[name="A"]' => array('value' => 'all'),
       ),
       'invisible' => array(  // you choose 'invisible' parameter
          ':input[name="B"]' => array('value' => 'all')
       )    
    )
)