mainStack.Alignment = UIStackViewAlignment.Leading;
       mainStack.Spacing = 10;
       mainStack.Axis = UILayoutConstraintAxis.Vertical;
       mainStack.Frame = new CGRect(10,10,Frame.Width - 30,Frame.Height - 100);

mainStack1.Alignment = UIStackViewAlignment.Center;
        mainStack1.Spacing = 10;
        mainStack1.Axis = UILayoutConstraintAxis.Vertical;
        mainStack1.Frame = new CGRect(5, 5, Frame.Width - 30, Frame.Height - 200);