title: Pattern for implementing INotifyPropertyChanged?
body: <p>I have seen the following pattern used for implementing INotifyPropertyChanged</p>
  
  <pre><code>private void NotifyPropertyChanged(string propertyName)
  {
      PropertyChangedEventHandler handler = PropertyChanged;
      if (handler != null)
      {
          handler(this, new PropertyChangedEventArgs(propertyName));
      }
  }
  
  public event PropertyChangedEventHandler PropertyChanged;
  </code></pre>
  
  <p>Can someone explain to me the necessity of the <strong>var handler = PropertyChanged</strong> assignment prior to checking it for null versus directly checking <strong>PropertyChanged == null</strong> directly?</p>
  
  <p>Thanks</p>