title: question about KVO and the method "observeValueForKeyPath"
body: <p>can you help me understand the observeValueForKeyPath method : </p>
  
  <p>here it seems that observeValueForKeyPath is called because we changed the value "for the key : earthquakeList" , but let's say we have another key observed, like "earthquake_New_List", </p>
  
  <p>how can i know that the first, or the second key observed, has changed, if we only have one callback method, the observeValueForKeyPath ?</p>
  
  <pre><code>[self addObserver:self forKeyPath:@"earthquakeList" options:0 context:NULL];
  //...
  - (void)insertEarthquakes:(NSArray *)earthquakes
  {
      // this will allow us as an observer to notified (see observeValueForKeyPath)
      // so we can update our UITableView
      //
      [self willChangeValueForKey:@"earthquakeList"];
      [self.earthquakeList addObjectsFromArray:earthquakes];
      [self didChangeValueForKey:@"earthquakeList"];
  }
  
  // listen for changes to the earthquake list coming from our app delegate.
  - (void)observeValueForKeyPath:(NSString *)keyPath
                        ofObject:(id)object
                          change:(NSDictionary *)change
                         context:(void *)context
  {
      [self.tableView reloadData];
  }
  </code></pre>
  
  <p>Thanks</p>