public string MyStringProperty
{
  get
  {
    object s = ViewState["MyStringProperty"];
    if( s == null )
    {
      s = "MyDefaultValue";
    }

    return (String)s;
  }

  set { ViewState["MyStringProperty"] = value; }
}

public bool MyBooleanProperty
{
  get
  {
    object b = ViewState["MyBooleanProperty"];
    if( b == null )
    {
      b = true;
    }

    return (bool)b;
  }

  set { ViewState["MyBooleanProperty"] = value; }
}

public string MyStringProperty
{
  get { return ViewState.GetValue("MyStringProperty", "MyDefaultValue"); }
  set { ViewState["MyStringProperty"] = value; }
}

public bool MyBooleanProperty
{
  get { return ViewState.GetValue("MyBooleanProperty", true ); }
  set { ViewState["MyBooleanProperty"] = value; }
}

internal static class MyExtensions
{
  public static T GetValue<T>(this IDictionary bag, string key, T defaultValue )
  {
    object value = bag[key];
    if( value == null )
    {
      value = defaultValue;
    }

    return (T)value;
}