/// <summary>
/// Add child view controller to parent controller's view.
/// </summary>
public static void AddChild(this UIViewController that, UIViewController viewController)
{
that.AddChild(viewController, null);
}
/// <summary>
/// Add child view controller to parent controller's view.
/// </summary>
public static void AddChild(this UIViewController that, UIViewController viewController)
{
that.AddChild(viewController, null);
}