title: INotifyPropertyChanged - Event stays null
body: <p>I am trying to implement the following INotifyPropertyChanged Extension:</p>
  
  <p><a href="https://stackoverflow.com/questions/527602/automatically-inotifypropertychanged">Automatically INotifyPropertyChanged</a> (accepted answer)
  <a href="http://ingebrigtsen.info/2008/12/11/inotifypropertychanged-revisited/" rel="nofollow noreferrer">http://ingebrigtsen.info/2008/12/11/inotifypropertychanged-revisited/</a></p>
  
  <p>But I cant figure out why my PropertyChanged EventHandler stays null. :(</p>
  
  <p>I did a very simple WPF Application to test it out, here is my XAML Code:</p>
  
  <pre><code>&lt;StackPanel Orientation="Vertical"&gt;
      &lt;TextBox Text="{Binding Path=SelTabAccount.Test, UpdateSourceTrigger=PropertyChanged}"&gt;&lt;/TextBox&gt;
      &lt;TextBox Text="{Binding Path=SelTabAccount.TestRelated, UpdateSourceTrigger=PropertyChanged}"&gt;&lt;/TextBox&gt;
  &lt;/StackPanel&gt;
  </code></pre>
  
  <p>And my code behind:</p>
  
  <pre><code>public partial class MainWindow : Window, INotifyPropertyChanged
  {
      public event PropertyChangedEventHandler PropertyChanged;
  
      private TabAccount _selTabAccount;
  
      public TabAccount SelTabAccount
      {
          get { return _selTabAccount; }
          set
          {
              _selTabAccount = value;
              PropertyChanged.Notify(() =&gt; this.SelTabAccount);
          }
      }
  
      public MainWindow()
      {
          InitializeComponent();
  
          SelTabAccount = new TabAccount()
          {
              Test = "qwer",
              TestRelated = ""
          };
      }
  }
  
  public partial class TabAccount : INotifyPropertyChanged
  {
      private string _test;
  
      public string Test
      {
          get { return _test; }
          set
          {
              _test = value;
              PropertyChanged.Notify(() =&gt; this.Test);
              PropertyChanged.Notify(() =&gt; this.TestRelated);
          }
      }
  
      public event PropertyChangedEventHandler PropertyChanged;
  }
  
  public partial class TabAccount
  {
      private string _testRelated;
  
      public string TestRelated
      {
          get
          {
              _testRelated = Test + "_Related";
              return _testRelated;
          }
          set
          {
              _testRelated = value;
              PropertyChanged.Notify(() =&gt; this.TestRelated);
          }
      }
  }
  </code></pre>
  
  <p>In the code behind you will see one class (its partial for just random testing) with 2 properties that should notify a property change but nothing happens.</p>
  
  <p>The NotificationExtension is a copy and paste from the links provided at top and is in a external cs file.</p>
  
  <p>I have also tried to do the sample with the "normal" INotifyPropertyChanged implementation and this works as expected but I cant make it happen with this extension class.</p>
  
  <p>Hope you can help me figure it out.
  Thanks in advance.</p>