title: INotifyPropertyChanged in UserControl
body: <p>I have a custom control which is inherited from TextBox control.
  I would like to implement the <code>INotifyPropertyChanged</code> interface in my custom control.</p>
  
  <pre><code>public class CustomTextBox : TextBox, INotifyPropertyChanged
  {
      public event PropertyChangedEventHandler PropertyChanged;
      protected void NotifyPropertyChanged(string info)
      {
          if (PropertyChanged != null)
              PropertyChanged(this, new PropertyChangedEventArgs(info));
      }
  }
  </code></pre>
  
  <p>My problem is when I try to raised a PropertyChanged event the PropertyChanged event handler is always null.</p>
  
  <p>Anybody can help me?</p>