title: How to stop the Observer in NSNotification to called twice?
body: <p>I have an observer of <code>NSNotification</code> which is called twice. I do not know what to do with it.</p>
  
  <p>I googled it but no solution found.</p>
  
  <pre><code>[[NSNotificationCenter defaultCenter] addObserver:self
       selector:@selector(connectedToServer:) name:@"ConnectedToServer" object:nil];
  
  - (void)connectedToServer:(NSNotification*)notification {
  
      [[NSNotificationCenter defaultCenter] postNotificationName:@"SendMessageToServer" object:message];
  }
  </code></pre>