Adding a StackLayout to a Scrollviewer

So I have constructed my StackLayout with all my children in it. Now if I set this StackLayout to be a child of another StackLayout I can see the items perfectly.
E.G

SL.Children.Add(MainLayout); works... But I cannot scroll this so the items go off the screen.

but

SV.Content = MainLayout doesn't show anything.

What am I doing wrong?