title: PropertyChanged event always null
body: <p>I have the following (abbreviated) xaml:</p>
  
  <pre><code>&lt;TextBlock Text="{Binding Path=statusMsg, UpdateSourceTrigger=PropertyChanged}"/&gt;
  </code></pre>
  
  <p>I have a singleton class:</p>
  
  <pre><code>public class StatusMessage : INotifyPropertyChanged
  {   
      private static StatusMessage instance = new StatusMessage();
  
      private StatusMessage() { }
  
      public static StatusMessage GetInstance()
      {
          return instance;
      }
  
      public event PropertyChangedEventHandler PropertyChanged;
      private void OnPropertyChanged(string status)
      {
          if (PropertyChanged != null)
          {
              PropertyChanged(this, new PropertyChangedEventArgs(status));
          }
      }
  
      private string statusMessage;
      public string statusMsg
      {
          get
          {
              return statusMessage;
          }
          set
          {
              statusMessage = value;
              OnPropertyChanged("statusMsg");
          }
      }
  }
  </code></pre>
  
  <p>And in my main window constructor:</p>
  
  <pre><code>StatusMessage testMessage = StatusMessage.GetInstance();
  testMessage.statusMsg = "This is a test msg";    
  </code></pre>
  
  <p>I cannot get the textblock to display the test message. When I monitor the code through debug, the PropertyChanged is always null.  Any ideas?</p>