Grid Chidren.Add

var grid = new Grid ();
grid.RowDefinitions.Add (new RowDefinition { Height = GridLength.Auto });
grid.RowDefinitions.Add (new RowDefinition { Height = new GridLength (1, GridUnitType.Star) });
var stacklayout1 = new StackLayout { HeightRequest = 100, BackgroundColor = Color.Red };
var stacklayout2 = new StackLayout { BackgroundColor = Color.Blue };
Grid.SetRow (stacklayout2, 1);
grid.Children.Add (stacklayout1); grid.Children.Add (stacklayout2);
MainPage = new ContentPage { Content = grid };