Refreshing a Grid

Longtime ASP.NET developer, I'm pretty new to Xamarin.

I have a Grid that I am constructing in code-behind. When I change it in code-behind, it does not visually change in the UI. Basically I want to display the data in a simple grid as that data gets collected.

Here's my XAML:

<ScrollView HeightRequest="100">
    <Grid x:Name="grid">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Label Text="TL" Grid.Row="0" Grid.Column="0" />
        <Label Text="TR" Grid.Row="0" Grid.Column="1" />
        <Label Text="BL" Grid.Row="1" Grid.Column="0" />
        <Label Text="BR" Grid.Row="1" Grid.Column="1" />
    </Grid>
</ScrollView>

I put in four cells just for testing. These four cells display initially but never change. Here's my code-behind that is executed on a button-click:

    private void updateGrid(List<MyStringData> data) {
        grid = new Grid();
        grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) }); //Field1
        grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) }); //Field2
        grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) }); //Field3
        grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) }); //Field4

        int i = 0;
        foreach (MyStringData r in data) {
            gridPitches.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
            gridPitches.Children.Add(new Label() { Text = r.Field1 }, 0, i);
            gridPitches.Children.Add(new Label() { Text = r.Field2 }, 1, i);
            gridPitches.Children.Add(new Label() { Text = r.Field3 }, 2, i);
            gridPitches.Children.Add(new Label() { Text = r.Field4 }, 3, i);
            i++;
        }
    }

This method apparently does nothing. Do I need to tell the grid or view to redraw or something?