title: register a class in objective c
body: <p>lets say i have <code>classA</code> which is a class  of audio,that sample the audio input many times.
  each time <code>class A</code> get a new data (can happen many times in second), he needs to inform another class, which is <code>classB</code>.</p>
  
  <p>Now, i could just make an instance of <code>class B</code>  in <code>classA</code> and call B when there is a new data arrived, but this is not a modular software.</p>
  
  <p>i want <code>classA</code> to be "blind" to the outside, and just to add him to every project, and to have another <code>classB</code> that will <code>register</code> him some how, so when A has something new, B will know about it,(without A calling B ! )</p>
  
  <p>how its done right in objective c ?</p>
  
  <p>thanks a lot .</p>