title: value changed eventhandler
body: <p>I want to react, whenever an integer value has changed. So, is there a possibility to write an own eventhandler? I need to get the old value and the new one, because I have to de-reference some events for an object in a list with the index of the old value and reference these events to the listitem with the index of the new value.</p>
  
  <p>Something like this (really abstract):</p>
  
  <pre><code>value.Changed += new Eventhandler(valuechanged);
  private void valuechanged(object sender, eventargs e)
  {
       list[e.Oldvalue] -= some eventhandler;
       list[e.newValue] += some eventhanlder;
  }
  </code></pre>
  
  <p>Thanks.</p>