title: self IBAction and sender
body: <p>I am a newbie iOS programmer, here is my question:
  I have mapview and segmented control, also changeMapType function which get called when UIControlEventValueChanged occures, like this</p>
  
  <pre><code>// change map type with segmented control
  - (IBAction)changeMapType:(id)sender
  {
      NSInteger i = [mapTypeControl selectedSegmentIndex];
      if (i == 0){
          [worldView setMapType:MKMapTypeStandard];
      }
      if (i == 1) {
          [worldView setMapType:MKMapTypeSatellite];
      }
      if (i == 2) {
          [worldView setMapType:MKMapTypeHybrid];
      }
  }
  </code></pre>
  
  <p>and in viewDidLoad I want to call this method to set up which map type is first.</p>
  
  <pre><code>[mapTypeControl setSelectedSegmentIndex:2];
  [self changeMapType:nil];
  </code></pre>
  
  <p>above code works fine, but below code works fine either</p>
  
  <pre><code>[mapTypeControl setSelectedSegmentIndex:2];
  [self changeMapType:self];
  </code></pre>
  
  <p>so finally, what to pass as SENDER? which is correct?</p>