WPF

public partial class MainWindow : Window, INotifyPropertyChanged
{
  public MainWindow()
  {
    InitializeComponent();
  }

  private void Button_click(object sender, RoutedEventArgs e)
  {
    Age = Age == 10 ? 11 : 10;
  }

  private static int age = 10;

  public static int Age
  {
    get { return age; }
    set
    {
      if (age == value) return;
      age = 10;
      RaisePropertyChanged("Age");
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;

  private void RaisePropertyChanged(string propertyName)
  {
    PropertyChangedEventHandler handler = PropertyChanged;
    if (handler == null) return;
    handler(this, new PropertyChangedEventArgs(propertyName));
  }
}

http://10rem.net/blog/2011/11/29/wpf-45-binding-and-change-notification-for-static-properties[^]

There are two ways to notify the binding system of property changes, both of which follow the same pattern as their instance-based relatives. The first is to create a static event named <propertyName>Changed. The second approach is to create a single event which is the static version of the INPC PropertyChanged event named StaticPropertyChanged.

public static event EventHandler AgeChanged;

static int age = 10;
public static int Age
{
    get { return age; }
    private set
    {
        age = value;
        
        var handler = AgeChanged;
        if (handler != null) handler(null, EventArgs.Empty);
    }
}

private void Button_Click(object sender, RoutedEventArgs e)
{
    Age = (Age == 10) ? 11 : 10;
}

public static event EventHandler<PropertyChangedEventArgs> StaticPropertyChanged;

private static void NotifyStaticPropertyChanged(string propertyName)
{
    var handler = StaticPropertyChanged;
    if (handler != null) handler(null, new PropertyChangedEventArgs(propertyName));
}

static int age = 10;
public static int Age
{
    get { return age; }
    private set
    {
        age = value;
        NotifyStaticPropertyChanged("Age");
    }
}

private void Button_Click(object sender, RoutedEventArgs e)
{
    Age = (Age == 10) ? 11 : 10;
}