Animate StackLayout's height

How can I animate the height of StackLayout (expand and collapse)?

I've tried Animate extension method, but it looks like it has a bug:

public class App : Application
{
    public App()
    {
        var stackLayout = new StackLayout
        {
            BackgroundColor = Color.Red.MultiplyAlpha(0.25d),
            VerticalOptions = LayoutOptions.Start,
            Children =
            {
                new BoxView{ Color = Color.Red, HorizontalOptions = LayoutOptions.FillAndExpand, HeightRequest = 50 },
                new BoxView{ Color = Color.Blue, HorizontalOptions = LayoutOptions.FillAndExpand, HeightRequest = 70 },
                new BoxView{ Color = Color.Olive, HorizontalOptions = LayoutOptions.FillAndExpand, HeightRequest = 40 },
            }
        };

        double calculatedHeight = 0f;

        stackLayout.SizeChanged += (sender, e) => 
        {
            if (Math.Abs(calculatedHeight) < 0.0001d)
            {
                calculatedHeight = stackLayout.Height;   
            }
        };

        var button = new Button
        {
            VerticalOptions = LayoutOptions.Start,
            Text = "Hide",
        };

        var page = new ContentPage
        {
            Content = new StackLayout
            {
                Children = { stackLayout, button }
            }
        };


        button.Command = new Command(() => 
            {
                var animate = new Animation(d => stackLayout.HeightRequest = d, calculatedHeight, 0);
                animate.Commit(stackLayout, "BarGraph", 16, 3500);
            });

        MainPage = page;
    }
}

Adding ForceLayout did nothing.

Also I've tried animate the height of RowDefinition, but it doesn't work too:

public class App : Application
{
    public App()
    {
        var stackLayout = new StackLayout
        {
            BackgroundColor = Color.Red.MultiplyAlpha(0.25d),
            VerticalOptions = LayoutOptions.Start,
            Children =
            {
                new BoxView{ Color = Color.Red, HorizontalOptions = LayoutOptions.FillAndExpand, HeightRequest = 50 },
                new BoxView{ Color = Color.Blue, HorizontalOptions = LayoutOptions.FillAndExpand, HeightRequest = 70 },
                new BoxView{ Color = Color.Olive, HorizontalOptions = LayoutOptions.FillAndExpand, HeightRequest = 40 },
            }
        };

        var button = new Button
        {
            VerticalOptions = LayoutOptions.Start,
            Text = "Hide",
        };

        var grid = new Grid { };
        var stackLayoutRow = new RowDefinition { Height = 172 };
        grid.RowDefinitions = new RowDefinitionCollection
        {
            stackLayoutRow,
            new RowDefinition { Height = GridLength.Auto }
        };
        grid.Children.Add(stackLayout, 0, 0);
        grid.Children.Add(button, 0, 1);

        Animation animation;

        button.Command = new Command(() =>
            {
                if (stackLayoutRow.Height.Value < 172)
                {
                    Debug.WriteLine("Show");
                    animation = new Animation(
                        callback: (d) =>
                        {
                            stackLayoutRow.Height = Clamp(d, 0, double.MaxValue);
                        }, 
                        start: stackLayoutRow.Height.Value, 
                        end: 172, 
                        easing: Easing.Linear, 
                        finished: () => animation = null);
                    animation.Commit(owner: grid, name: "AnimationTag", rate: 16, length: 1000);
                }
                else
                {
                    Debug.WriteLine("Hide");
                    animation = new Animation(
                        callback: (d) =>
                        {
                            stackLayoutRow.Height = Clamp(d, 0, double.MaxValue);
                        }, 
                        start: 172, 
                        end: 0, 
                        easing: Easing.Linear, 
                        finished: () => animation = null);
                    animation.Commit(owner: grid, name: "AnimationTag", rate: 16, length: 1000);
                }
            });

        var page = new ContentPage
        {
            Content = grid
        };

        MainPage = page;
    }

    private static double Clamp(double value, double minValue, double maxValue)
    {
        if (value < minValue)
        {
            return minValue;
        }

        if (value > maxValue)
        {
            return maxValue;
        }

        return value;
    }
}

I'm using Xamarin.Forms 2.1.0