gistfile1.txt

// MainPage.xaml.cs

public RowDefinitionCollection MyRows { get; set; }

public MainPage()
{
    InitializeComponent();
    
    // Magic happening here
    MyRows = (RowDefinitionCollection)new RowDefinitionCollectionTypeConverter().ConvertFromInvariantString("Auto, 100, *, 50");
    
    BindingContext = this;
}

// MainPage.xaml
<?xml version="1.0" encoding="utf-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="TestSwitch.MainPage">
  <Grid RowDefinitions="{Binding MyRows}">
      <Frame Grid.Row="0" BackgroundColor="#2196F3" Padding="24" CornerRadius="0">
      <Label Text="Welcome to Xamarin.Forms!" HorizontalTextAlignment="Center" TextColor="White" FontSize="36" />
  </Frame>
      <Label Text="1" Grid.Row="1" />
      <Label Text="2" Grid.Row="2" />
      <Label Text="3" Grid.Row="3" />
  </Grid>
</ContentPage>