public class Invoker
{
  Controller controller = new Controller();
  controller.IsOpen = true; // this line will trigger show the dialog
  controller.IsOpen = false; // do nothting
}

public class Controller
{
  public bool IsOpen
  {
    get { return _isOpen; }
    set
    {
      _isOpen = value;
      if (_isOpen)
      {
        this.ShowDialog();
      }
    }
  }
  private bool _isOpen;

  private void ShowDialog()
  {
    // code to handle dialog show
  }
}