StackLayoutExpandSample.cs

var stack = new StackLayout
{
    Children =
    {
        new BoxView
        {
            HeightRequest = 100,
            BackgroundColor = Color.FromHex("cccccc")
        },
        new BoxView
        {
            HeightRequest = 50,
            BackgroundColor = Color.FromHex("ffaaaa"),
            VerticalOptions = LayoutOptions.EndAndExpand
        },
        new BoxView
        {
            HeightRequest = 50,
            BackgroundColor = Color.FromHex("aaffaa"),
            VerticalOptions = LayoutOptions.CenterAndExpand
        },
        new BoxView
        {
            HeightRequest = 50,
            BackgroundColor = Color.FromHex("aaaaff"),
            VerticalOptions = LayoutOptions.StartAndExpand
        },

    }
};